After a day of school, Umezawa, along with his friends, Takemura and Matsuda catch up to fellow student, Makunouchi Ippo, and began insulting and beating him underneath a bridge. Trying to provoke a reaction from the submissive high-schooler, they are stopped by a jogging Takamura Mamoru, who scares them away by dodging their punches and stealing the buttons off their school uniforms with his impressive footwork.
Then one day, as Ippo was going to the Kamogawa Boxing Gym, Umezawa and his friends mess with Ippo, taking his boxing licence. Umezawa is surprised as Ippo defends himself and takes his boxing licence back from him. After Ippo's match with Oda Yūsuke, Umezawa and his friends approach Ippo and asks how he won. Umezawa then asks about Ippo's next match. The group then runs away, originally wanting to apologise for picking on him.
On the day of Ippo's match against Fujiwara Yoshio, Umezawa and his friends watch as Ippo wins, with Umezawa coming to the conclusion that Ippo is strong. The next day, Umezawa forces Ippo to meet his gang, calling Ippo his friend as he introduces him.
Umezawa watches Ippo's match against Jason Ozuma.
Eventually, Ippo gets his right hand drugged in order to fight Sendō Takeshi. Umezawa and his gang attends Ippo's match against Sendō in Osaka, where they are greatly outnumbered by the home crowd's cheers. On graduation day, Umezawa forces Ippo to take pictures with the gang and several other students to keep memories of their friendship. On the way home they come across the bridge from before, where Umezawa tries again to apologise to Ippo but before he can, Ippo innocently assumes he is trying to ask when the next match will be. Umezawa realises that Ippo views him as a friend, and decides to let the past go.
After school, he finds employment as a salary man but soon quits his job in order to be a mangaka and write a boxing manga about Ippo. He later learns that Ippo can't box because his mother is hospitalised, ultimately forcing him into an early retirement. Knowing that he will not be able to write the manga if Ippo retires so soon, he asks to work at the Makunouchi Fishing Boat. After the first day he almost reluctantly quits on Ippo, but after seeing Ippo practising his jabs, he decides to go through with it for his friend (he would later be thanked personally by Kamogawa Genji for this). Before Ippo's match against Saeki Takuma, he receives a pair of boxing trunks that is designed by Umezawa, who tells him not to fall, as it would be bad advertising. Umezawa then gives Ippo a new pair of boxing shoes. Before the match against Saeki begins, Umezawa visits Ippo's room and attempts to take a photo of him, however the camera roll flies out. After watching the match against Saeki, Umezawa attempts to take a photo again, however the camera roll flies out again.
After Ippo's match against Alexander Volg Zangief, Ippo is passed out for three days, with Hiroko worried, Umezawa promises himself to work hard at the fishing boat to make Hiroko not worry about it. When Ippo's match against the champion Date Eiji comes up, Umezawa brings Ippo's teacher to watch the match. Umezawa then cheers for Ippo as he watches, he is then saddened when Ippo loses.
Sometime before Ippo's fight against Sawamura Ryūhei, Umezawa wrote a one-shot manga about his experiences on the fishing boat to submit to a publisher. After letting Ippo read it (and after redoing a few pages that were accidentally torn up by Takamura and Aoki), he decided to retire from Makunouchi Fishing Boat in order to pursue his dream. During his farewell party, he tried to confess to Ippo's mother that he was the one who gave Ippo all those bruises during high school but was unable to finish because she had already figured it out, and told him to always hold his head up high without looking back with regrets.
Before leaving, he asked Ippo what he should tell people when asked how they know each other, but left before he could get an answer. Ippo used the fishing boat to chase after him and tell him that they know each other as "classmates, acquaintances, co-workers... but most importantly best friends", resulting in a tearful yet joyful goodbye.
Not long before Itagaki Manabu's Rookie King match against Imai Kyōsuke, Ippo and Itagaki learned that Umezawa had gotten a job as an assistant to a professional manga artist and decided to pay him a visit. It was revealed that his one-shot debut manga, Ma Ippo Get You!, had won the Rookie Manga Award. Umezawa currently lives in a one-room apartment and has grown his hair out longer and has a small mustache. However, he still cheers on Ippo and attended Itagaki's Rookie King match.
Since then, Umezawa has cleaned up his appearance, retaining a minor goatee and trimming his hair. He's been working as an assistant to the artist who does the weekly comic "The Town You're In," a Slice of Life romantic comedy made for kids, spin-off of "A Town Where You Live". Umezawa still keeps up with Boxing Fan and was upset about Ippo being mocked by Kojima Hisato.
- "He's strong." - Round 26 (manga) Round 12 (anime), Umezawa changes his opinion after seeing Ippo box for the first time
- In some ways, Umezawa can be viewed as Morikawa Jouji's avatar character.