Kumi Mashiba (間柴久美, Mashiba Kumi) is a recurring character in Hajime no Ippo.
As a child, she was a fan of Baldychu from the Pokamon series. When Kumi was 13 years old, she lost both of her parents in a Car accident. Without her parents, Kumi and her brother would begin a life depending on each other. Kumi and Ryō were over their parents graves, Kumi was crying repeating,' What are we going to do?'. Ryō started his oaths.
Around middle school, when ever she was interested in a boy and they accompanied her home after school, they would run straight into her brother. After he stared them down, they would eventually lose to the pressure and run away. The pattern would repeat a lot to where she never been on a date before.
In the anime, while Makunouchi Ippo was doing roadwork, he noticed Kumi riding a bicycle. He saw her again at the entrance of the Kōrakuen Hall when he and Takamura Mamoru were going to his pro test. Ippo saw her a third time while walking to school after his fight against Oda Yūsuke.
Kumi, during Miyata Ichirō's first match in the East Japan Rookie King Tournament against Takada Teruhiko, looked for her seat listed on the ticket and asked Ippo for help. At the time, Ippo had his pants unzipped accidentally, which surprised her. After Miyata won the match, Kumi wondered why "he" wants to box so much.
After Ippo's match against Hayami Ryūichi, Ippo returned to the Yamanka Bakery, where he met Kumi again. After finding out that Ippo was a boxer, with some trepidation, Kumi wished Ippo luck with it. Ippo left, thinking she was still a fan of Miyata's. When Mashiba Ryō was fighting against Miyata, she was watched the match, which Mashiba won in the end.
A few days after Miyata lost the match to Mashiba, Ippo visited the bakery again. He noticed Kumi was now sad, which Ippo believed she was depressed that Miyata lost. In an attempt to cheer her up, Ippo started mentioning that Miyata should have won the match if his opponent did not cheat. Kumi stopped Ippo, telling him to stop stating bad things about her brother, Mashiba, wondering how someone who doesn't know her brother make him out to be a villain.
When Kumi returned to her apartment with her brother, she began cooking for him. She mentioned Mashiba's boss (Tanaka) been helping them along, but Mashiba disagreed since he had a bad attitude where something bad would eventually happen, even though he had been working there for a year. Mashiba then told her that with boxing, he would be able to make money to stop her worries as he progressed to eventually the world championships. Kumi, however, did not care about being rich, she just could not take her brother feeling pain for her, fearing that one day her brother is going to breakdown.
During her brother's match against Ippo, Kumi hoped that Mashiba would not get seriously hurt in it. When Kumi saw Mashiba taking a lot of punches, she did not want to watch anymore and left the arena. Kumi then ran into Tanaka, who dragged her back in order to cheer for Mashiba. In the end, Mashiba lost the match.
At the dressing room, Kumi waited with Mashiba while he was resting. Kumi wanted Mashiba to stop boxing, but Mashiba realised he needed to start over again, since it is a world that draws him. After hearing that, Kumi decided to cheer Mashiba on. Later, Kumi had quit the bakery after Mashiba's match to work at the Tanaka Transportation with Mashiba.
Ippo was sent to the Kawai Hospital after his victory in the Class A Tournament against Alexander Volg Zangief. When he woke up, Kumi saw him and informed him that Mashiba had also won the Class A Tournament. Later, Kumi went to Ippo's celebration party where she was invited by Reiko, who was offered to come to the celebration party by Takamura, Kimura Tatsuya and Aoki Masaru. The group then played a game of bowling at the Rosa Bowl, with the first winner getting to pick first which girl they want to go out with. At the end of the game, Ippo went out with Kumi. After escorting her home, they had a short conversation before Ippo got scared of Mashiba and left.
After Mashiba became the JBC junior lightweight champion, Kumi called Ippo in order to help celebrate his win. When Ippo arrived, the apartment was dark, and only Mashiba was there. Kumi eventually arrived and celebrated the win with them. On the way home, Kumi walked Ippo to a taxi, Kumi mentioned that she would prepare a party for Ippo if he became champion.
After Kumi heard that Ippo lost the match against champion Date Eiji, Kumi called Ippo to ask him on a date since he was free. Ippo agreed to go on a date with her on Sunday. Ippo decided to take Kumi to the Kōrakuen Amusement Park. During the date, Kumi mentioned how her brother would scare a lot of boys that she liked and could never get a date. She also told Ippo that she was concerned about her brother boxing, she wanted to be able to help him in any way possible, where she started studying hard to become a nurse. During the haunted house ride, Kumi was left behind when Ippo thought he saw Mashiba in it.
Kumi was asked by Tomiko to watch and cheer for Aoki, Kimura, and Takamura's matches with her. After Aoki and Kimura won, Kumi looked for Ippo. She became jealous when she saw Ippo talking to another girl. The next day, Kumi stopped by the Kamogawa Boxing Gym to celebrate everyone's win, but Aoki and Kimura were not there. Instead, Kumi followed Ippo doing his roadwork on a bike. She asked Ippo for an autograph since she wanted to be the first girl that gets one, and he agreed to it once they return to the gym. On the way back, she asked Ippo why he started boxing, but he did not answer. When Ippo arrived at the gym, he met Mari, who wanted to interview him. When Kumi saw Mari get an autograph from him, she got mad and left after leaving a "baka" sign outside the gym.
Kumi called Ippo to ask him something, which Ippo used as an opportunity to ask her about a date, which Kumi accepted. Ippo decided to take her to the Shimono Zoo. During the date, Kumi apologised for leaving the "baka" sign since she wanted to be the first to get Ippo's autograph. Kumi was then delighted to hear that Ippo would give her his first autograph as a JBC champion. When Ippo's match against JBC champion Sendō began, Kumi watched with her brother, where Ippo was declared the winner.
Kumi attended a birthday and victory party for Ippo following his match with Sendō at the Sugar Ray. Kumi didn't know it was Ippo's birthday, so she didn't bring a gift for him. A few days later, Kumi called Ippo to meet up again. Wanpo followed Ippo to the meeting, where Kumi gave Ippo a late birthday present, a new jogging suit. Ippo gave her his autograph that he promised. Kumi mentioned she will hold his gift dear since she doesn't think she will be seeing him again, and takes off running.
The next day, Ippo found out that Kimura would be fighting Mashiba for the JBC title. Ippo tries calling to tell her boxing is a sport, no matter who wins or loses it, should stay in the ring. However, Mashiba ends up answer the phone, and disagrees. Ippo is able to meet Kumi later to tell her the same thing, and she agrees, but thinks they shouldn't meet for awhile.
After finding out that Sanada is popular with the nurses where Kumi works, he is pressured by his gym mates to confess to her, and ultimately almost does so as when he is alone with Kumi in the snow. However he chickens out, leaving her visibly upset as she was expecting it. She is also angry that he seems to not care who she cheers for, and only makes up with him after his victory over Sanada.
After Ippo vs Hammer Nao match, Kumi goes on a trip to the beach with Aoki, Tomiko, and Ippo. While there, they run into Takamura, Itagaki Manabu, Kimura, and Wanpo, who are in a training camp. When Takamura sees Ippo and Kumi, he gets angry but Ippo is saved by Hachi and Nekota Ginpachi, who are also visiting the beach.
Later on, Ippo and Kumi find out the vacation isn't a day trip, where Aoki and Tomiko also book two rooms to stay over night. Aoki's plan is for Ippo and Kumi to stay the night together, in order to make Ippo a man. Kumi thought she would be staying with Tomiko, not Ippo. When Ippo and Kumi go out for some fresh air at night on the beach, Ippo starts to tell Kumi a ghost story, which scares her and bring her closer to Ippo. However, they end up running into a shocking scene involving Aoki, Tomiko, and Takamura on the beach when the fireworks explode in the background.
Back in the hotel room, Kumi drinks a little too much beer (while Ippo's only had one), and she starts talking about the past with Ippo when they first met (in the bakery according to Kumi), and how happy it made her when they meet. Ippo then interrupts her to confess, but he starts to chicken out but continues. He starts to confess to her with a long introduction but when he tells Kumi that he loves her, Kumi fell asleep since Ippo took too long with the introduction. While she didn't hear Ippo's confession, he is still happy that he was able to say it.
The next day, Kumi and Tomiko continue to enjoy the beach while Aoki and Ippo try to get revenge on Takamura. That night, everyone (but Takamura) goes to the beach to enjoy the fireworks. In the background, Takamura's trying to get some revenge on them for not including him by aiming fireworks at them.
Prior to Ippo's match with Shimabukuro Iwao, when Ippo reached peak physical exhaustion, Kamogawa told Ippo that he is not to practice or work out for a full week. He mentions if Ippo wants to do something, he can only soak in a pool. Aoki mentions he will get someone to keep an eye on him. In the local swimming pool, Kumi catches Ippo trying to work out and stops him since Aoki told Kumi that Ippo isn't suppose to do anything but rest. Itagaki and Nanako show up too, where Kumi starts to get mad at Nanako when she mentions her age. Nanako mentions that she hasn't heard Ippo has a girlfriend, which makes Kumi wonder what her relationship with Ippo is.
Kumi and Nanako talk about their brother being boxers. Kumi doesn't like to go to the match since they scare her, but Nanako does since she thinks fighting men are all cool. Kumi is a little jealous of her positive attitude on it. Nanako mentions she is jealous of Ippo and Kumi's relationship. When Kumi ask "What relationship?" Nanako thinks there is a little space available or she has a chance if she works hard. While they are talking, Ippo thinks that female friendships is a beautiful thing. After Ippo is done, he goes out to eat with Kumi.
After the match, Nanako visits Ippo, and learns he has been sleeping the last two days. Ippo's mother tells her it is okay to check in on him while he is sleeping. Kumi visits a little later, and catches Nanako trying to kiss Ippo while he is a sleep. Kumi mentions she is here to take care of Ippo since she is a nurse.
While she is fighting with Nanako, Iimura Mari enters Ippo's room and criticises them for being too noisy. Mari is stopping by in order to interview Ippo, but won't happen while he is still out. Instead, she search thru Ippo's bedroom, looking through his photo albums with Nanako. Kumi doesn't want to look without Ippo's permission. Kumi wonders if Mari is also interested in Ippo too.
Mari notes based on how Kumi and Nanako are acting, they never made it far in their relationship with Ippo if they never been in his bedroom before. Mari mentions that she is interested in Ippo, which shocks Nanako and Kumi. Kumi tries to get them to leave in order for her to take care of Ippo since she is a nurse, which cause tem to start fighting with each other. Ippo's mother enters with some tea for them. She mentions that when Ippo is like this, she tries to let him sleep as peacefully as she can, which makes Nanako, Mari, and Kumi feel guilty, and they decide to leave.
Prior to Ippo's match against Sawamura Ryūhei, during the weigh in, Kumi is waiting outside with her brother. She brought lunch for Ippo since she thinks he will be hungry. Mashiba followed Kumi after Ippo called her last night, where he thinks a boxer that wants to meet a girl before a match is pathetic. He wants to see how pathetic Ippo's face is since has heard that Sawamura has an attitude. He mentions that maybe Ippo's ball shrunk, which embarrass Kumi after she hears it. Ippo's running a little late, and Kumi's getting nervous since it been a while since she seen him.
A while later, Ippo finally arrives. Ippo is surprised when he sees Mashiba with her. They head toward kouraku park to eat. Along the way there, Mashiba notices a motorcycle, where he wonders if he should just ride it. Kumi tries to stop him since it is someone's back. Sawamura arrives when he sees Kumi nears and throws a punch at her. Ippo blocks the punch, but it still nicks Kumi, where it grazes her face.
Ippo starts to confront Sawamura about it, when Mashiba starts throwing a punch that Sawamura dodges. Mashiba wants to kill Sawamura, but Ippo stands in front of Mashiba and tells him that he will be the one who'll do it in the ring tomorrow. Kumi heads home to tend to her wound, and Ippo ask Kumi to come to his match tomorrow, where he will fight at full strength. Mashiba tells him fighting at full strength isn't enough, he need to shred him into eight pieces.
Ippo mentions that he plans to use (the Dempsey Roll Counter) no matter how many times in order to win, even though it might scrape away at his boxer life if he uses it more than two times. He will fill better if Kumi is there watching him since Ippo thinks it could end up being his last match.
On the way home, Kumi thinks something is wrong with Ippo since he's not acting normal. Mashiba thinks Ippo might be anxious since Sawamura is strong since he was able to dodge his fist easily. Kumi disagrees, and she think it is something else where she is worried about Ippo's match tomorrow.
During the match, Kumi doesn't care about the results, she just wants the match to end safely, where Ippo is able ot make it through okay. After watching Ippo take counter during the Sawamura, she ask her brother if Ippo will be alright. She hopes Ippo will come home okay after he was acting weird the day before. In the end, Ippo was able to win the match.
After the match, Kumi walks Ippo home since he is serious injured. Along the way home, Kumi ask Ippo again why he started boxing. She can understand why her brother started and he was always pretty violent, but she wonders why someone that is kind and mature like Ippo get interested in it. Ippo tells her he wanted to be strong.
Kumi thinks that since he is the JBC champion, he should know what it feels like now, but Ippo disagrees. It is true that he is physically strong, but he still hasn't reach "him" yet. His strength wasn't brute force, but the strength to live on. Kumi wonders if Ippo was talking about Miyata, but realizes he is talking about his father.
When they arrive at Ippo's house, Hiroko is shocked at Ippo's appearance. Ippo collapses and they take him to his room. Kumi and Ippo's mother talk not getting used to seeing a loved one like that. Kumi ask Ippo's mom about Ippo's father. She thinks that no matter how much she worries about Ippo, he will never stop boxing when he looks up to his father. Ippo's mom jokes about it being hard for Kumi having to worry about two men. She doesn't think Ippo will stop since he is pretty stubborn man, ever since he was a boy when he got something in his mind he would see it through to the end. Ippo's mother begins to talk about Ippo's father.
When Kumi's about to go home, Ippo's mother wants call Kumi a cab since its getting late, but Kumi thinks she will be fine alone. Ippo's mother notices a strange man waiting outside, but Kumi tells her that is her brother. On her way home with her brother, she mentions to Mashiba she wants to visits their parents graves.
During Miyata Ichirō training camp with Takamura Mamoru, he wonders if there is a chance that Takamura might have a detached Retina, where he calls Ippo about it. In order to learn more information about it, Ippo asked Kumi for some medical books about it. She labeled what he wanted to know. After reading it, she wonders if Ippo's eye is bothering him. She was worried Ippo wanted it for himself and got worried. Kumi wonder if one of Ippo's friends might have it since it can be a major problem among boxers. She asks if she should recommend a good doctor about it, but Ippo declines and ask her to keep it a secret.
After Takamura's match against David Eagle , Kumi is helping Ippo and Itagaki train by timing their sprints. Itagaki wonders if Ippo is free this Saturday. Ippo, Kumi, and Itagaki Nanako mention they are free. Nanako thinks that was a close one, where she can't let her guard down with Kumi. Ippo tries to disagree, but tries to change the subject. Kumi thinks Itagaki is really into training, and mentions that he can win the Rookie King if he wins two more matches. Nanako mentions her brother is going to win, unlike someone's brother (Mashiba), but Kumi mentions he almost won it (while Ippo apologises for winning.) When Itagaki returns, he mentions he is not in the mood for fun.
Later, while Nanako at Ippo's house waiting for Itagaki, she talks to Kumi on the phone to rub her face in the fact that she and Ippo going out this Saturday. Kumi wonders why she is calling from Ippo's house, and Nanako mentions that is how her and Ippo are, before Ippo takes over the phone to explain things. He tells Kumi that this Saturday he is going to see who Itagaki will face in the Semi-Finals in the Rookie King Tournament, where he promises that he will go out with her next time. Kumi mentions she is fine with it, but it bothers her. When her brother asks for food, she doesn't answer and glares at him. Mashiba realise that he need to grab some take-out instead.
A few days later, Mashiba mentions to Kumi that he heard that Kumi was helping out with the enemy's training. Kumi wonders what he means since Ippo is in a different weight class, but Mashiba still thinks Ippo is the enemy. Kumi wonder why he still has a grudge about it, and wonders who told him about it. Mashiba mentions Itagaki told him, when Kumi notices Mashiba has a black eye.
Later on, Kumi notices Mashiba leaving in a hurry, and wonders where he is going. He tells her that he is going clothes-shopping with someone, which shocks her. She calls Ippo about it, and mentions Mashiba has a date, which is something that's never happen before, and she is worried about it. She tells Ippo that she decided to follow Mashiba and see, but she is too scared to do it alone. Ippo realizes that Kumi is similar to her brother. Ippo asks she is telling him, and she points that Mashiba is 5 meters away, which catches Ippo off guard.
Ippo doesn't think it is surprising that Mashiba might be getting attention from women since he is a JBC Champion, but they end up being shocked when they see it is actually Itagaki. Kumi is a disappointed that it is only Itagaki, and not a women. Kumi and Ippo over hear Itagaki telling Mashiba information about them, when they spent a night together in a hotel. Mashiba can't believe a man and women spend a night together and nothing happened.
Itagaki thinks it is bad that Ippo and Kumi aren't making any progress, but Mashiba likes it that way. He will never accept Kumi going out with Ippo, but Itagaki wonders if Mashiba would say the something thing if the guy wasn't Ippo. Itagaki think's Mashiba's attitude isn't right. Kumi is a nice lady, and she doesn't have a boyfriend, where Mashiba is part of the reason why. Mashiba starts to get angry, where Kumi wants to stop them, but Itagaki mentions that Kumi is an adult where Mashiba should let her make her own decision. If Mashiba tries to repress her, she might end up rebelling. Mashiba realises Itagaki might be right, but still won't accept it. Itagaki mentions as someone with a little sister, he understands his feeling. Ippo walks Kumi home, where they discuss about Mashiba. When Kumi arrives home, Mashiba doesn't ask her where she was, which sort of creeps her out.
After Ippo's match against Karasawa, Kumi stops by while Ippo and Itagaki trying to drop off a drink for Itagaki that her brother uses when he is watching his weight. When she notices, Itagaki sister isn't there she is happy, which reminds Itagaki that Imai wanted to meet his sister if he won, since he is interested in her. Itagaki doesn't like it bring such a thing into a man to man fight, which makes Ippo and Kumi think of their situation with Mashiba, where Ippo realises he could never say that. Itagaki doesn't care who his sister dates, but him since he is the enemy, where he would rather die, which makes Ippo and Kumi think of their situation. Kumi plans to go cheer for him, when Nanako stops by, which makes Kumi made when she see her hugging Ippo, which makes her want change her mind in hope that Itagaki loses instead.
Kumi watches Itagaki's match against Imai with Itagaki's family and Umezawa. In the end, Itagaki is declared the winner after six rounds, but he is heavily injured where he need to be carried out with a stretcher, and sent to the hospital later. Itagaki ends up injuring his achilles tendon and broken his left fist in it.
Itagaki get sent to Kawai Hospital, where Kumi helps look after him. Kumi tells Itagaki not to use his hand or foot until he is better rested. Itagaki enjoys have Kumi look after him. Imai visits Itagaki, where he gets into an argument with him once Nanako stops by. Kumi returns to yell at Itagaki for not resting, that causes Itagaki and Imai to calm down, which annoys Nanako.
A few days later, Kumi see Itagaki leave the hospital, and she reminds him to rest now that he is released. Ippo picks up Itagaki in a truck, while Imai offers to walk Nanako home, which Kumi comment that Nanako should do it since they would make a good couple. That makes a Nanako a little angry, and tells Imai she though he wasn't suppose to talk to her since he lost the match. Imai walks away determined to beat Itagaki in a rematch. Kumi thinks mean hate to admit they lost, and Nanako mentions that if she has something to lose why wouldn't you try to keep it while walking away. Kumi ponders about her brother that has a match coming up, where boxers never seem to have any time to relax.
After Ippo's match against Take, Ippo and Kumi attend Miyata's match against Che. When Kumi see's Ippo's face covered with bandages she becomes worried about him. She enjoys spending time together. When the match is about to start she ask Ippo who is fight since she came without even knowing what's going on. When Ippo is about to answer, Mashiba answer instead. Kumi tells Ippo that she didn't invite him, but Ippo guesses that Mashiba found out about it from Itagaki.
They go in to watch the fight, where Ippo learns that Mashiba doesn't have opponent yet for his match decided, since no one wants to fight him. Mashiba mentions there is one guy that he has to "pay back". Ippo wonders who it could be, but Mashiba said who said it was a junior lightweight, which makes Ippo thinks he is talking about him. Mashiba asks Kumi why she is with that loser, but she tells him its none of Mashiba's business. Mashiba tells Kumi that Ippo will be fighting Miyata next, which causes to be scared a little since her brother also fought him. Kumi has a hard time following the match, after she see Miyata KD Che fast.
After the Miyata wins the match, Kumi asks Ippo if he wants to go out to eat. He does, but they run into Iimura Mari and Fujii Minoru who offer to take them out for a meal where the editorial department pays for it. Kumi doesn't want Ippo to agree since she would rather eat alone with him, but Mashiba agrees to it instead and drags Ippo.
After learning that Mashiba will be fighting Sawamura Ryūhei, Kumi ask Ippo about a comment he made in Monthly Boxing Fan. She asks why he didn't think Mashiba is going to win. She's not mad at him, but she is been really worried lately about her brother. He hasn't got in trouble lately, where she was hoping that he has started to settle down. But Mashiba's been mentioning that "I'll Kill him" ever since his match was decided, where he's gone back to how he was.
She is worried about him after he has gotten so much nicer and things were peaceful, where she is now worried about him. Ippo tries to calm her down, when he realises why Mashiba is acting that way since Mashiba really cares about his sister and enter the ring as her big brother. He thinks inside the ring he will be a demon like no one has ever seen before.
Later on, Kumi offers to fix something for Mashiba to eat, but he can't eat much since he is on his weight control. Mashiba tells Kumi not to come to his next match. Kumi ends up going to the match, and runs into Ippo, Itagaki, Aoki, and Kumi. She mentions that she thought about heading home since she is worried it might be a blood bath. Itagaki doesn't think she should, and offer his ticket to her so she can sit next to Ippo. Kumi tells Ippo that Mashiba didn't want her to come, Ippo tells her not to worry, since Mashiba will win. But Kumi doesn't think her bad feeling has to do with winning or losing.
After Mashiba lost his match against Sawamura Ryūhei, Kumi attend a baseball game that Ippo, Itagaki, and Takamura took part in for Kimura and Aoki's local business team. Since it doesn't involve fighting and anyone getting hurt, Kumi is able to cheer a lot, and she is able to enjoy herself. Along with Nekota and Nanako, Kumi was able cheer their team to victory.
After Ippo's match against Jimmy Sisphar, Kumi visits Ippo while he is fishing. When she notices that Ippo looks bored and Nanako isn't around, it is chance for a date. She asks him if he want to go to the pool since it is summer and she bought a new swimsuit. Ippo wants to, however he is still heavily injured from his match, where he still has stitches in, and his leg is still damaged. She decides to stay with him instead..
In order to talk about something, Ippo starts talking about boxing, which is something Kumi doesn't want to hear, and Ippo apologises for it. Kumi tells Ippo not to worry about since she just likes spending time like this. She thinks that when she is with Ippo, time seems to flow by so much more easily. She feels at peace and more relaxed. She mentions that if she goes home, she can't really relax since it is tense there with Mashiba.
Ippo asks about Mashiba's suspension (from the Sawamura Ryūhei match) and wonders what he has been up to. Kumi tell him that Mashiba hasn't said anything, but she thinks he really wants a match since he is really tense all the time. Kumi feels like she the one who's tense all the time though, since Mashiba always makes her worry so much. She doubt he ever even considered how she feels waiting at home for him. Ippo disagrees since he thinks Mashiba cares about her.
Kumi thinks Mashiba probably doesn't care about that kind of stuff when he's in a match, where Mashiba only thinks along the lines of if it means I won't lose or if I can win somehow, I don't care if I live or die, where he doesn't even bother to think about how she feels. Kumi apologises for it, and tells Ippo that she gotten a lot more used it by now. She knows boxers aren't going to stop just because you tell them it's dangerous.
Besides, sooner or later, she knows Mashiba will have to stop anyway. Until then, she will just keep on asking him to make it back in one piece and making sure that he knows that she is waiting. She then asks Ippo to make it back in one piece.
Prior to Ippo's match with Malcolm Gedo, in order to solve the mystery to Gedo's magic punch, Ippo asks Kumi from a medical perspective if she know of anyone whose arm could extend and shrink back. Kumi doesn't think so since it's not like people's joints are made of rubber, but she does know that some people can dislocate their joints easily, where if it is dislocated then it will extend further than it normally would.
Ippo wonder if it is possible for someone one to do it regularly. Kumi thinks someone might be capable of doing it, but the stress over time would become a chronic problem. If she knew someone doing that, she would advice them personally to stop. She wonders why Ippo wants to know, and Ippo mentions he is going to see a "Magic Show" first hand and he is hoping to be able to dissect it before hand.
After Kumi hears that, she wants to go too. Ippo tells her it will be a Kourakuen Hall, but the date hasn't been decided yet. Kumi ends up becoming disappoint when she learns Ippo is talking about boxing again. Ippo's been worried about it where he had trouble sleeping and waking up in the mornings from it.
Kumi thinks she been worried about something too. Ippo and her have known each other for a few years now, but he still speaks so formally with her, this polite and reserved conversation. She guesses that she is just "an acquaintance" to him, but Kumi wants Ippo to act more friendly with her. She thinks the space between them hasn't shrunk any over time. She feels that Ippo doesn't intend on closing the gap between them any time soon.
When Kumi arrives at her place, she wonders if Ippo thinks they've gotten a lot closer, since he takes a slow pace with everything except boxing. She feels that he's the type who strengthens a relationship very slowly and carefully. After thinking about it, she sort of prefers it that way too since she doesn't know how she will handle it if Ippo suddenly asked her to go steady. She decided that she shouldn't worry about whether or not their relationship has gotten any tighter. While thinking that, Mashiba mentions his shirt has gotten tigher and shrunk in the wash, and complains to Kumi about it.
Kumi stops by while Ippo and Itagaki are working while Itagaki Nanako is there. While she is spending time with Ippo, Nanako and Itagaki becomes jealous, with the latter thinking Ippo has a cute girlfriend. Nanako disagrees with him since she doesn't think Kumi is his girlfriend.
Ippo mentions to Kumi that Mashiba should have a return fight now that his suspension is almost over. Ever since Kumi's watched his match against Sawamura, she been really worried, and she doesn't think she is able to watch his return match alone. Ippo offers to go with her (since he wanted to watch it anyway), Kumi appreciate it.
Ippo notes this Mashiba match back is a OPBF title fight, where he interested to see how Mashiba fights against the champion after so much down. After hearing that, Kumi is starting to get more worried. Ippo adds once Mashiba wins, he thinks will have a World title match in pretty soon too, which makes Kumi more worried. Ippo tells her it will be fine, and Ippo thinks Mashiba can win it without getting hurt, but Kumi actually worried that he might seriously hurt his opponent. Ippo tries to calm her fears, but it doesn't help. She tanks Ippo for being worried about her. They plan to cheer on Mashiba.
While Ippo is training, Kumi sees Wanpo slide down a hill on a board left on the hill, and Ippo chases after him. Ippo asked if she came to see him, and Kumi wondered if she needs a reason to visit him. Ippo doesn't know what to say, when Kumi mentions she stopped by because of her brother. His match is coming up, and she scared to go see it by herself, but she doesn't want to see him fouling anyone again. She's all the family he has, so she needs to go. Ippo tells her planning to go since Itagaki's is fighting in the match before his anyway, and he wants to cheer them on together.
Ippo and Kumi are trying to think of something else to talk about, when Kumi see Ippo shadow boxing again. She wonder if she should head home, since he is doing that. She notices the cherry blossom petals falling, and thinks it is beautiful, like in a romantic moment. Kumi asks what Ippo is thinking about, and he mentions boxing again, which makes her mad. Kumi decides to head home, but she and Ippo end up slipping on a board and falls down on it, where Ippo is placed on top of her. Kumi thinks he is about to kiss her, Wanpo starts barking which ruins the moment, and Kumi ends up sledding down the hill on a board.
Kumi ends up developing a bit of a serious problem because of that incident. Lately, she has been reacting erratically to a certain keyword "slip". Kumi can't get over it, since she was so close to being kissed, and doesn't think there is no way that she will get a second chance like that with Ippo ever again. She thinks she is one of those women who always slips up at the most crucial moments.
During an operation that she is assisting on as a nurse, when the doctor mentions "slip", Kumi ends up stabbing him with a scalpel. When Kumi see a fly slips on a bald patients head, she ends up hitting the patient after seeing that. Kumi thinks something is wrong with her. While at home, Mashiba watches TV and mentions that the comedian "slipping" around on stage, resulting in Kumi throwing a plate at Mashiba.
At Mashiba's match, while meeting Ippo, she hears Saeki Takuma mentioning Ippo is with his girlfriend, and Ippo doesn't disagree with him. It makes her motivated again. She and Ippo watch Itagaki win his match easily. Nanako arrives after his match, and she starts to mess with Kumi, after Nanako mentions her drink "slipping" out of her hands. Kumi thinks she must have learned about her issue from Itagaki.
When Mashiba's match is about to start, Mashiba gets a low cheer from the crowd, where Kumi mentions that Mashiba's boss, Tanaka, started a Mashiba fan club. During Mashiba's match, Kumi starts to hug Ippo when she sees Mashiba slipping and getting fouled. When Mashiba sees that, it makes him angry since he thinks Ippo is trying to take advantage of the situation. When he wins the match, Mashiba ends up throwing his gloves at Ippo.
After getting some free tickets from Kimura Tatsuya for Nermina Park. an amusement park, Ippo decides to take Kumi to it. When Kumi sees Itagaki Manabu with Iimura Mari she is happy (while Mari seems bored.) They also see Tomiko and Aoki Masaru.
They start to talk about Kimura, and mentions he is a "pedo-anime" lover. Ippo doesn't think there is nothing wrong with it since they are all boxing nerds. Kumi tells them she loves anime, and she watches a lot of it. Aoki says that is fine, but does she watch the pedo stuff? Itagaki thinks it is fine as long as Kimura doesn't act on it.
Ippo tries to tell everyone Kimura isn't like that since he has a girlfriend, but Itagaki and Aoki thinks he was just lying to get them off the topic. Ippo doesn't think Kimura would lie about it, and Kumi agrees. They decide to call him, and they catch him with a little girl at the amusement park too. Aoki calls the police on him.
Mashiba and Kumi attend Ippo's match against Kojima Hisato. Prior to the match, they run into Date Eiji, Saeki Takuma, Okita Keigo, and Sendō Takeshi. Sendo and Mashiba start to getting into it, while Date tells that losers should learn to get along. That makes Sendo and Mashiba angry, while Okita tells them to show Date some respect.
Date adds on that its okay since they are bitter that he won. Sendo mentions he barely won, which is nothing to brag about. Date calls him a two time loser, and starts to get into it. Kumi tries to get Mashiba to ignore them and go inside. He does, but Sendo and Date mock him for losing to Ippo and Sawamura and consider him teh weakest. Mashiba starts yelling at them, which is drawing attention to them. Kumi yells at them to stop. They do, and all head inside.
After Takamura Mamoru's awful match against Peter Rabbitson, Kumi follows Mashiba to the Mayweather Bar after Date Eiji invited him along with Okita Keigo, Saeki Takuma, and Sendō Takeshi to celebrate Takamura's and Ippo's wins. After a few drinks, Date and Sendo get into a disagreement about him defeating Ricardo Martinez. Mashiba adds his thoughts about it, which makes the the atmosphere more tense. Kumi tries to play peacemaker between them, since she is worried there would be trouble if she didn't come along. Mashiba and Sendo start to get into it, while Saeki tries to help her calm things down.
Date (while drinking) asks them why they are angry, but then adds he knows it is because of Takamura. He criticises Takamura's match and his poor performance in it. Date thinks Sendo might be disappointed with it after coming from Osaka for it. Sendo agrees. Okita, Saeki, Mashiba and Kumi decided to complain about Takamura in order to lighten the mood. After Mashiba mentions Takamura's Panda outfit, Kumi is about to agree with him when she noticed it at the bar. They then all notice Takamura sitting there with it.
Takamura gets up to start to leave, but he decides to block the exit instead. Date continues to increase the tension by criticizing Takamura, which scares Mashiba, Sendo, Okita, and Mashiba. Mashiba tells Kumi to go out the back exit while he tries to buy time. Kumi tries to get them to stop and not fight, but (drunk) Date tells her to either back them up or be quiet. Date asks Takamura that if he think he can fight with this group (Date, Mashiba, Sendo, Saeki, and Okita) and not expect to come out of it in one piece. They charge at him and end up getting into a bar fight. They end up losing, and Kumi putting bandages on them after the fight.
The next day, Kumi visits Ippo house after she hears from Itagaki that he was sick, but Ippo tells her it is just a fever. Ippo mentions that Kamogawa gave him some good advice about violence is bad. Kumi agrees with him, and she thinks about the night before (the bar fight) where she is angry about how stupid all of them were since they should have know no good could have come out of it.
After Aoki Masaru lost to Iga Shinobu in the Class A Tournament, he is sent to Kawai Hospital. Kumi tells everyone that he is stable, and once is swelling and fever go down, he will be examined by a specialist and most likely to be released.
After Ippo's spar with Sendō Takeshi, his customers have caught some extra fish and give it to him. Ippo decides to head to Kumi's place to drop some off. After Ippo drops off the fish and starts to head home, Kumi ask Ippo for some help in how to prepare and cook the fish. Ippo's debating on staying, but agrees to it after he finds out Mashiba isn't home. In the kitchen, Ippo start to explain things to her, while she is preparing the fish. A fish scale goes flying and hits Ippo in the bandaged eye, where Kumi puts her hand on Ippo's face (in a romantic gesture.) Kumi apologices for it, and continues to descale the fish, which ends up hitting Ippo more. Ippo and Kumi continue to enjoy their moment together.
Mashiba arrives outside complaining something stinks. Ippo and Kumi are sitting down while waiting for the food to cook. Kumi asks if Ippo will eat it with her, and Ippo agrees. While they wait, Kumi offers to replace Ippo's bandage since it is pretty dirty. They come close to kissing, but the mood is ruined when Mashiba when he mentions the pot is about to boil over. Kumi runs toward it, while Ippo starts climbing the wall.
While Kumi is away, Mashiba asks Ippo how far they got. While Ippo is trying to explain they were in the kitchen make food, Mashiba misheard him thinking he said they were making kids. Mashiba continues to bully Ippo, and Kumi ends up throwing the ladle at him to get him to stop. They eat dinner together, when Mashiba hears Ippo helped make it, he says the food tastes bad, which makes Kumi angry. Mashiba continues to complain about it while he leaves the table, but Kumi thins it tasted pretty good.
While he is leaving, Mashiba asks Ippo who beat him up. Ippo mentions Sendo. Mashiba asks Ippo that he beat Sendo twice, but he let Sendo beat the crap out of him? Ippo disagrees since he thinks Sendo is stronger than he used to be, where he thinks he is lucky he beat him in the first place. Mashiba asks him he trains to make it home in one piece right (or something similar)? Kumi doesn't think there is nothing wrong with that.
Ippo mentions he has his mother waiting home for him after matches, where he is prepared for it, but he would still rather come home safely so she doesn't worry as much. Even if he is covered in bandages and bruises, he wants to be able to walk home using his own two feet. Mashiba asks is that the kinda of things a guy aiming for the World title should say? Ippo and Kumi doesn't see anything wrong with it, but Mashiba adds it is no wonder he got his ass kicked, where he thinks Ippo has gotten weak. When Ippo leaves, Kumi starts hitting Mashiba for ruining the mood.
After Ippo lost his match with Alfedo, Ippo goes for a walk. He runs into Takamura a long the way, Itagaki, Kimura, and Aoki follow after him. Kumi rides a bike to catch up to him later, yelling at him for walking around when he should be resting. Kumi mentions she went to Ippo's house but he wasn't there, and she took one of their bikes after Umezawa told her that he would be here.
She decided to pay Ippo a visit after she heard about how Ippo's match went. She thought Ippo based on Mashiba's comment, that this one had the best KO in it, where she assumed Ippo won. She planned on coming to congratulate Ippo in this morning, but she was shocked when she saw the paper. Ippo asks Kumi for the paper, and she hands it to him. She didn't believe until now after seeing his face swollen. After reading the article, Ippo finally realises he lost. Kumi decides to walk Ippo back to his place, to get him some ice and bed rest.
Along the way home, Kumi is holding Ippo's arm. She asks Ippo if he looked in the mirror yet, since his face is all swollen. Kumi thinks that anyone who cares about him would be worried after seeing his face like that, and wonders why he can't just stop boxing. Ippo mentions that Kumi is always so nice to him. Win or lose, where he ends up forgetting things. He knows how dangerous it is to keep fighting matches like that.
Kumi asks that since Ippo was the JBC champion, he doesn't have anything to protect or any duty to keep fighting anymore. Ippo agrees with her, but he still plans on going back to the ring. He thinks he made the same mistake again, where he didn't enter the ring with the desire to win. He feels that he betrayed "their expectations" again, where he can't quit after something like that. He doesn't want to quit, not after that. Kumi wonders if that is the reason why Ippo gets into the ring to box, or if he thinks it is really worth it? To become the World Champion for something like that? Ippo is shocked after hearing that. Ippo mentions that he knows, and doesn't want his mother to worry too much, so he claims that the next time he loses, he will retire.
After showing signs that Ippo might be punch drunk, Kamogawa told Ippo to rest and not training. Ippo starts wearing leg weights to train instead. In order to get used to them, Ippo goes bowling with Kumi, since the twisting is similar to the Dempsey Roll. While bowling, Kumi is performing well and Ippo is getting a lot of gutter balls. Aoki, Kimura, Takamura, and Itagaki end up joining them which ends up ruining their time together.
When the Kamogawa crew, see Ippo scoring zero, they worry that he might be punch drunk, but Takamura see Ippo wearing weights on his arms and legs. Aoki tries wearing them, while bowling but does poorly. Others want to try to, but Kumi (while mad) interrupts them saying it is her. She proceeds to throw it. Takamura mentions that Ippo is bowling to build up the new Dempsey Roll. Ippo agrees, and he plans to continue to do so until he get used to it.
After Ippo's lost against Antonio Guevara, Kumi stops by the Makunouchi Fishing Boat to check on him. As requested by Hiroko, Kumi stays with Ippo while Hiroko leaves for work. After realising he is fine, she starts crying, believing it might be for the best that he retires so he doesn't have to struggle and suffer anymore, wanting to always be by his side as she loves him. She then falls asleep next to him.
When the two wake up, Ippo is surprised to see Kumi next to him and leaves for fishing. Kumi and Hiroko talk about waiting and worrying about Mashiba and Ippo as boxers, concluding that Ippo may just make a fist and go on a new adventure.
That night, Ippo walks Kumi home. During the walk, Kumi suggests Ippo a specialist that will check him for Chronic Traumatic Encephalopathy (CTE), the clinical term for being Punch Drunk and has a good reputation for treating patients in combat sports. Kumi mentions that she wants to be there to help Ippo with everything in a tender moment that ends up getting ruined by Mashiba, who came to pick her up.
Now that Ippo's retired, Kumi and him start to go on dates. They go and see a movie. On the way home while discussing the movie, they run into Mari. She is covering the Otowa Gym in the area. Ippo starts to talk about Imai, but Mari wants to ask Ippo something instead. Before Mari asks it, Kumi steps in and ask her to refrain from talking about boxing. This is not the right time or place for that. Mari disagrees, but Kumi believes that Ippo is doing his best to forget about boxing, and she doesn't want Mari to start trying to lure him back with that kind of talk.
Kumi mention Mari needs to think how Ippo must feel, but Mari counters with is that what Ippo wants or what Kumi wants. Mari thinks Ippo has already considered all the issues and made up his mind about it. She is not trying to change Ippo's mind about retiring, but if he's just injured, then it is natural for Ippo to take some time off in order to heal.
Mari knows there is no reason for Ippo to forget about something he dedicated himself to for so long, and that he should be proud of it. Mari questions if Kumi just feel sorry for Ippo that he had to leave the ring because he may be punch drunk. She then asked Ippo about his current condition, and Ippo says he had headache which scares Kumi, but Ippo think it is because of a cold.
Mari then asked Kumi if she realises what she might be getting into by being with him since she is a nurse. Kumi mentions that if anything happens, she is prepared to take care of Ippo. But she is glad that Ippo stopped before it came to that, since it would be too much for her to take of both of them (referring to Ippo and her brother).
Mari realised that Kumi was worried that she would have look after more than one badly injured person. Mari apologises to Kumi, and says she won't mention boxing at all. Ippo then brings the subject back to boxing again, making Kumi shocked. Mari comforts Kumi, and wonders how dense Ippo can be since Kumi was talking about looking after him long term, basically admitting that she wants to get married. She thinks Ippo really is useless outside of boxing. Kumi asks Mari what she think about Ippo, and she says she loves him, but as a Pro Boxer. Mari feels sorry for Kumi, and wouldn't want to compete against her (for now.) Ippo wonders what Kumi and Mari were discussing, but Kumi mentions just a little girl talk, where it's a secret. Ippo mentions his mom was going to make dinner tonight, and it will probably be done by the time they return.
Along the way home, Ippo thinks he loves Kumi, and wonder if he can tell her how he feels since he thinks she's kind of oblivious about it. Kumi is wondering the same thing about Ippo. She think if it were to happen, it would be amazing, and Ippo think it would be terrifying. They both know it would change their relationship in an instant. Ippo decides not to say it since things are fine as they are. When they return to the house, they discover Nanako there. Nanako apparently helped Ippo's mom make tonight's dinner. Nanako mentions she dropped by to visit and she saw Ippo's mom slaving away in the kitchen trying to cook up this big dinner because "some dumb girl dragged her son away, probably helping him work up a huge appetite." So she decided to stay and help out.
She mentions that ever since Itagaki quit working there, she hasn't heard anything about Ippo because everyone (but Kumi according to Nanoka) has been trying hard to give Ippo some space. So Nanako decided to show up in person. Kumi mentions that she wouldn't call what Ippo and her are doing as "going out", she is just trying to fill the empty gaps of his day now that he's not boxing. Kumi and Nanako get into a small fight, and precede to pull each other cheeks.
Nanako decided to do the same with Ippo, and wondered if there is anywhere Ippo wanted to go or see. The only thing Ippo wanted to do is help people. He wants the family business to be a success, but since so many people have supported him for so long, he wants to give something back somehow.
After hearing that, Nanako mentions "So I really wish you would have become the World champion." Kumi doesn't want to talk about boxing. Nanako wonders what is wrong with talking about what's in the past, but Kumi fears that it will remind Ippo of it and drag him back to it. Ippo mentions that boxing was really important to him, so he doesn't think he can ever forget about it. But right now, he has no regrets and he doesn't have a reason to go back.
He misses somethings about it, and he doesn't feel like he did everything he wanted, since there was a promise he wasn't able to fulfil (showing the new Dempsey Roll to the coach) where it ended up being a lie. However, since Ippo tried his best, he can be sure of himself when he says, "That I'm sorry I couldn't do more and thank you for everything." Ippo mentions that there really wasn't a lot that he was proud of before he started boxing, but he is satisfied with that he's changed thanks to it, and that is why he doesn't have any reason to go back. Ippo asks his mom if she thinks he has changed, but she isn't sure. All she can say that she is relieved that he retired. Worrying and waiting wasn't easy to do.
For her, it was less about him changing, and more about making it back safe in one piece. She think that Ippo being okay with not being able to box might be a temporary feeling, but if Ippo is able to accept the quiet life for now, she can relax and enjoy this time with no complaints about it. Kumi agrees too. Nanako understand what she is saying since her brother is also a boxer, so she decides to not mention boxing for a while. Kumi is glad Ippo's mother mentioned that. Kumi realises Ippo was a good boxer, so everyone is sad about what happens where they keep reminiscing about it. But if anyone tries to interrupt Ippo's current peaceful life, she will get rid of them.
She is thinking, "Anyone, anything, in any way, she will eliminate anything to do with boxing, no matter who it is. I'll block them with everything I have." Ippo comments (while throwing punches) about everyone has stopped eating, and wants everyone to get back to enjoying the dinner, which makes Kumi mad. Wanpo starts barking because someone is at the front door.
Shinoda is knocking on the front door. Ippo is surprised by the visit it. Shinoda mention that he needs Ippo to come back to the ring (to be a 2nd), which makes Kumi angry. Ippo asks Shinoda what did he means about returning to the ring, when he already told the gym he's retired. Shinorda starts to explain, but Kumi tries to stop him and starts yelling at him instead, by really letting him have it. Shinoda apologises again. Ippo tries to calm Kumi down, in order to hear Shinoda out.
Shinoda says, "Can you please come back and help as a corner-man?" Ippo is surprised by it, while Kumi is still giving Shinoda the evil eye, but Shinoda continues to explains, "We're in trouble because we need more hands on deck. Think of it as helping out." Ippo is shocked about at the possibility of being a 2nd. Kumi thinks Shinoda is trying, little by little, to drag Ippo back into boxing, but Shinoda say it's not like they want him to fight again. Kumi believes Ippo will still have to deal with the stress of it, which could effect his health. She thinks Ippo needs more time to relax physically and mentally. Shinoda is starting to get afraid of Kumi.
Ippo's mom wants Kumi to go easy on, since she is scaring him, but Kumi believes Shinoda is only scared because he knows he is in the wrong. However, Nanako agrees that Kumi is way too scary. Kumi thinks it is silly since Shinoda used to be a boxer (and authory figure), and no way he would be scared from just her being angry. She thinks Shinoda is pretending to be scared in order to get her to let up on him. Except, Shinoda mentions that he is not pretending, but takes it back after getting scared again.
Kumi is getting angry that Shinoda is actually scared of her. Ippo's mom tells them to calm down, and give Shinoda a chance to speak. She asks how Shinoda is, and she notes that he is having a hard time speaking. Shinoda explains his past to her, but end up backfiring on him, when they ask him to clarify. Shinoda decides to leave instead of answering it, on the way out he mentions they are short handed, since Kamogawa is in the the hospital. Ippo is shocked when he hears that, and he wants to go visit him now, but Kumi tells Ippo visiting hours are over by now. Shinoda tells Ippo not to worry, Kamogawa just has a bit of a cold. Ippo is still worried about Kamogawa, and decides to visit him tomorrow. Ippo starts throw punches again, but stops after he notices Kumi looking at him. Kumi and Nanako decide to head home, and Kumi tells Ippo that he doesn't need to walk her home., which surprised Nanako that Ippo's been walking her home. Along the way home, Nanako is happy at the prospect of Ippo being a 2nd for Itagaki since it gives her another reason to go see his fights.
The next day, Ippo is fishing when Kumi stops by. He's not really trying to catch anything, but doing it to help him relax. Kumi asked about the coach. Ippo found out that Kamogawa already left the hospital, and he is resting at home now so he didn't get the chance to meet him. Yagi told him not to worry, but Ippo feels tha he needs to see him before he feels better.
Kumi thinks Ippo actually means that you want to make him feel better, which surprised Ippo. Kumi tells Ippo, "Your friends are in trouble, you can't ignore that and you want to help. You want to do what you can so the coach can rest easy." She thinks the only reason Ippo didn't say yes to becoming a 2nd right away is because he didn't want to hurt her feelings. Kumi thinks it is pretty obvious to how he really feels. Ippo tell Kumi that he is going back to boxing to be a cornerman. Kumi is sad, but she expected him to say it after she heard that the coach was in the hospital. She wished they had more time together, but she expect Ippo will be too busy to go out soon. Ippo disagrees with her, thinking they will still have time to go out. But Kumi knows that between working on the fishing boat, helping out with manga, and now being a second, Ippo will be even busier than when he was a boxer. She also noticed that Ippo seem to be happy about it, while she is the only one that feels lonely.
Ippo doesn't think that is true, but after thinking it over, he realise it is true. He didn't expect to be needed like this. He didn't think that boxing could still be a part of his life, or being of useful to anyone like that. Ippo is happy to return the ring, in any form. Kumi might not agree with Ippo choice to be a 2nd, but she does believe in him. She knows Ippo is going to try doing his best at being a second. Kumi knew it because she knows Ippo loves boxing too much to stop. She has faith that what Ippo is looking at now is something different from his past adventures, and she believes he won't be using his fists in the ring ever again.
The day after Ippo saw Miyata win his match, Kumi helps Ippo, who is out fishing. While Kumi is becoming better at fishing, Ippo believes he's not getting better at being a second, despite all three matches being wins. When Ippo says he saw Miyata's match two days ago, Kumi becomes scared, as she hears Miyata's name from both Ippo and her brother all the time and doesn't want Ippo drawn into boxing because of him. However, she is relieved when she discovers this is not the case.
After slapping Taihei Aoki, Ippo shaves his head and, for atonement, trains Taihei and Kintarō Kaneda. When Ippo meets with Kumi, he shows Kumi his bald head, which reminds Kumi of the "Baldichu" plush she had from the "Pokamon" series. Unable to resist, Kumi proceeds to kiss Ippo's bald head. Kumi stops herself and glares at Taihei and Kintarō after she notices them watching. Kumi then tells Taihei and Kintarō that the kiss didn't count and to erase it from there minds, scaring the two.
She is beautiful with short brown hair and dark coloured eyes, furthermore she isn't tall like her brother. In New Challenger, her body gains a paler/lighter skin tone.
In contrast to her brother, Mashiba Ryō, Kumi is quite cheerful and pretty. She first appears as a high school student and attracts the attention of many boys. However, her overprotective brother scares most of them off, resulting in her not having a boyfriend throughout her school years. She does not like boxing, but seems to have accepted it since the Ippo/Mashiba fight, which is also when she met Makunouchi Ippo. She disappeared for awhile afterwards but reappeared as a nurse after Ippo's fight with Volg Zangief. As a nurse, she often worries about Ippo and the other's wounds and even occasionally examines Ippo after his fights.
After meeting Ippo her feelings towards boxing have calmed considerably, but she still retains her basic feeling of wanting him and her brother to retire. She is often unable to cheer for even her brother and seems envious of Nanako, who can cheer for her own brother Itagaki quite easily. Also, after the Mashiba/Sawamura bout she told Ippo that she doesn't believe she will ever like boxing.
She and Ippo are in love with each other, but Ippo's clumsy personality and thick-headedness prevent their relationship from progressing at all, as well as the numerous intrusions from Nanako and Iimura Mari. Particularly, Nanako intentionally disrupts their time together, often claiming to be looking for Itagaki or just suddenly noticing them while walking by.
Although mostly different from her brother, when he went out to go clothes shopping with someone (Itagaki), she immediately called Ippo up to help her follow him, showing that she actually worries about him the same way he does for her. As she has become an adult she has also become a stronger woman, and has developed a habit of throwing objects at people (usually Mashiba) when her temper raises. She's arguably the only character in the entire series who has no reason to be afraid by her brother, and her comfort around him reflects this.
She has a hidden dark side that appears when someone gets in her way between Ippo. It makes her eyes look like her brother’s when she's angry. Kumi is able to give one menacing look to most people and they back down. She has done this to Taihei and Kintarō and they backed down immediately after seeing how evil she could be.
- "These are hot. They're fresh out the oven!" - Round 16, to Ippo during their second conversation at the Yamanaka Bakery
- "Is that why you get into the ring to box? Are you fighting to live up to everyone's expectations? Do you really think it's worth it? To become the World Champion for something like that?" - Round 1075, to Ippo after his loss to Alfredo Gonzales.
- "Even if you're not a boxer, even if something is wrong with you physically, I'll always be at your side." - Round 1207, thinking while watching Ippo sleep after his match with Antonio Guevara.
- According to the anime promotion site, Kumi (and Tomiko) works at Kawai Hospital (河合病院), which is a real hospital in Japan.
- Kumi's parents were killed in 1987, which would make her 13 years old at the time of their deaths.
- During the date to the Nermina Park, Kumi mentions she is a fan of anime.
- So far, Kumi has appeared on 3 manga covers - Volume 78, Volume 94(Background photo), and Volume 120.
- When Makunouchi Ippo meets Kumi the first time, his zipper is down. When Ippo meets her in the hospital after the Alexander Volg Zangief, his zipper is down again.
- Kumi has so far attended 5 boxing matches of Ippo, where he won.