He is a Filipino Boxing Manager in the Oriental and Pacific Boxing Federation. Mr. Sakaguchi is infamous for his impure motives and abandoning boxers who fail him. He has had a personal vendetta against Miyata Ichirō since he defeated his client Arnie Gregory to become the OPBF champion and is willing to do anything to end his career.
After Arnie Gregory finished off his sparring partner in a public spar for his OPBF title defence against Miyata Ichirō, Mr. Sakaguchi told the reporters that they were taking applications for future opponents. A reporter mentioned the match with Miyata was already set. Mr. Sakaguchi agreed that Miyata was sensational, however, Gregory won't lose. After further comments, Īmura Mari told him about Miyata's strength and believed that a boxer like his who is proud of his strength will find himself spinning his wheels and the joke will be on him. Mr. Sakaguchi believed that the Japanese reporters were blind and then revealed that they were holding back a technique called the "Bloody Cross" which would be shown during the match.
At the weigh-in, Miyata doesn't shake hands with Gregory, and mentioned to Mr. Sakaguchi that instead of searching for the next opponent, he should be searching for his next job once the match was over as Gregory would not have the belt nor would Mr. Sakaguchi have a job as his manager. Mr. Sakaguchi thought that rumours of Miyata's harsh weight control appeared to be true, and he won't have much strength in the ring, but his counters seemed quite excellent. He told Gregory that he should focus on that and teach him a lesson during the second half.
The next day, Mr. Sakaguchi and Gregory arrived to the Kōrakuen Hall for the OPBF featherweight title defence against Miyata. At the start of the match, Mr Sakaguchi noted that Miyata's colour looked better, but he believed that Miyata could not have replenished all of his strength in a single day. After the first round, Gregory mentioned he couldn't see the Cross Counter coming that sent him down, but Mr. Sakaguchi told him not to talk and to rest. Gregory claimed that he was caught off guard because Miyata was faster than he thought, but now knows that he will come for the bait again and fall. Mr. Sakaguchi added the instant he paints the cross again, it would become a cross of blood raining down on him. After the second round, Mr. Sakaguchi was surprised that Miyata was able to fight back in the condition he was in, wondering if it was that "Japanese warrior spirit" he heard of. Mr. Sakaguchi began making comments about Miyata that made Gregory tell him to stop making light of the match, threatening the end of his pay check. Gregory planned to give Miyata an honourable burial at full strength, and told Mr. Sakaguchi to shut up and watch.
After the third round, Mr. Sakaguchi told Gregory that he had many chances to finish him, and he believed that if he didn't soon, Gregory's commercial value would decrease and his performance would hurt his matchmaking credibility also. Mr. Sakaguchi was then dismissed by Gregory, not wanting to return to a corner that does not understand his boxer's feelings. Mr. Sakaguchi argued that they were under a contract, however, Gregory told him to leave after thanking him for bringing him a wonderful opponent. In the fourth round, Gregory was defeated by Miyata, leaving Mr Sakaguchi angered and leaving the hall alone. Mr. Sakaguchi then began to hold a grudge against Miyata.
In Thailand, Mr Sakaguchi arrived at Medgern Dachboy's house, where he saw that without help Dachboy's daughter would die. Sakaguchi noted that Dachboy didn't have money for a doctor. Dachboy told Sakaguchi that he need the fight money, and he didn't care who it was to show him the greatest fight ever. Mr Sakaguchi didn't care about it. He told Dachboy that he didn't care if he won, since he just wanted a chance to study his opponent as long as he can. He added that Dachboy was known throughout the Muay Thai ranks for his tought, where all he wanted him to do was last the entire fight. In order to heal his daughter, Datchboy agreed to act like a sandbag in the match.During Dachboy's match with Miyata, Mr Sakaguchi saw that Miyata improved his speed and abilities since his match against Arnie. He realised that Dachboy wasn't strong enough for him. Over the course of the match, Dachboy grew excited and wanted to have a serious and man to man battle with Miyata. He went all out against Miyata and even after being nailed a few times by his counters, he kept fighting. In a last resort attack against the champion, he was sent flying by Miyata's Counter. Dachboy wasn't moving, and Sakaguchi didn't care about what happened to him. He was able to see Miyata's greatest flaw duing the match.
Sakaguchi attended Miyata Ichirō's match OPBF title defence against Che Jounbong with Randy Boy Junior. He watched Miyata struggled in it after he became distract after spotting them in the crowd, where he ended breaking his fists but still able to pull threw. While Randy went to greet Miyata, Mr Sakaguchi waited outside Kōrakuen Hall for him. Later, he met RBJ, who told him that Miyata turned him down. Mr. Sakaguchi told him not to worry, since he will get that match for him. Randy added that if Miyata's fist weren't broken he wondered what would have happened. After he heard that, Mr Sakaguchi knew how to arrange their match now.
Later, due Miyata's broken fists, an interim OPBF Featherweight was created during Miyata's absents between #2 Randy Boy Junior and #3 Banai Jakkuim, since Makunouchi Ippo (#1 in OPBF) refused to take part. Randy Boy defeated Banai Jakkuim, and was declared interim OPBF Champion. A OPBF Title Featherweight Unification Match was then decided with Miyata Ichirō.
Sakaguchi attended Miyata's match against Donnie Sultan. He watched as Miyata defeated Donnie with a new punch. After the match, he ran into Ippo. He tried to sign Ippo to a contract, but Ippo turned it down. Mr Sakaguchi asked Ippo if he wanted a World Title match, but the condition was that he defeated his boxer, Randy Boy Junior, the new OPBF interim Champion. Since both of them are aiming for a World title match, they will probably clash in the future, where he would like to promote the match. Ippo told him that he had nothing to discuss with him since he believed Miyata wouldn't lose to his boxer. Mr Sakaguchi started laughing when he heard that, he told Ippo that he didn't know Miyata and Randy's history. He added to Ippo to look it up, and he will know that Miyata has no chance of winning. Mr Sakaguchi saw it, and it only made him more confident since counter will be useless in the match because history had already proved it.
After Randy defeated all the boxers at Otowa Boxing Gym, Randy Boy Junior was having a hard time finding training partners. Mr. Sakaguchi mentioned that they should have gone to Mexico instead of training in Japan. When Mari asked why he didn't, Otowa Coach commented it was because he was too cheap. Mr Sakaguchi asked if there was any other gyms they could call, that had a fast fighter (to prepare for Miyata, and to show off.) Otowa Coach doesn't think so when they heard about Randy Boy Junior destroying boxers. In order to find someone to eat his words, they begin to think of potential opponents for him. Mari thought of Itagaki.
Itagaki ends up fighting RBJ in a spar (with Ippo following along) and he loses. Ippo steps in the ring wanting to fight. However Sakaguchi breaks the fight up, saying he previously offered him a chance to fight Randy but he declined. After the spar, Randy Boy confronts Mr. Sakaguchi about it, only cares if he is able to delivers a World Title match later.
After Randy loses he claims he will never return to Japan again and then takes a bowel movement in the restroom and does not flush. Takamura happens to pass by and accidentally hits him in a fit of rage. The newspaper the next day has a headline of Sakaguchi saying he's never coming to Japan again, which causes Miyata to sigh in happiness.
Mr. Sakaguchi is the smallest adult in the story. He typically has a white mustache and white bushy hair and eye brows (similar to Don King.) He is typically seen wearing a business suit.
Mr. Sakaguchi tends to be arrogant, and looks down on people. When he first came to Japan, he tend to be over confident in his boxer's ability, and looked down on Japanese boxers and people. Mr. Sakaguchi tends to be petty, and he will carry a grudge if he is wrong, as his feud with Miyata has shown. He is willing to use his money or influence to get his way.
He is strongly interested in money. It was mentioned he could have took Randy Boy Junior to Mexico to spar with other boxer, but in order to save money, he took him to Japan instead. He tried to get Ippo to sign a contract with him, but Ippo refused.
- He has a lot of similarities in his managing background as real life retired boxing manager/promoter Don King.