|Manga Debut||Round 316|
|Anime Debut||Round 1 (New Challenger)|
|Voice Actor||Inaba Minoru|
A world famous boxing manager, Sakaguchi is infamous for his impure motives and abandoning boxers who fail him. He has had a personal vendetta against Miyata Ichirou since he defeated his client Arnie Gregory to become the OPBF Champion and is willing to do anything to end his career. Sakaguchi bares quite a resemblance in both appearance and personality as the infamous boxing promoter Don King.
He is first seen as the second for Arnie "Crocodile" Gregory , the OBPF champion, before Miyata took him down. After Miyata defeated Arnie, develops a grudge for Miyata and condescendendlly yelled at Arnie for losing. He returned again with another pawn from Thailand, Medgern Dachboy. Sakaguchi made a promise to Dachboy saying he would help his sick daughter if he could last all ten rounds with the OPBF Champion Miyata Ichirou, and that winning didn't matter. But during 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. After the fight, Sakaguchi claims to have discovered the "greatest flaw in Miyata's boxing".
Sakaguchi then has one more pawn he was sure would get the job done and destroy Miyata, who happens to be Randy Boy Junior. He provokes many of the Japanese for not being a challenge for Randy then Itagaki fights him and loses. Ippo steps in the ring wanting to fight. However Sakaguchi breaks the fight up, saying he priorly offered him a chance to fight Randy but he declined. 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 accidently 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.