First appearance: Battle 70
Age: 17
Type: Dou
Type: Katsujin Ken
Martial Arts: Karate

Mizunuma was formerly the second most bullied student in Kouryou High School, second to Kenichi. In the anime, he was to be picked as Daimonji's opponent, but Kenichi stepped in instead. Inspired by this act of courage, Mizunuma later joins Shinpaku Alliance as one of its pawns, and learns Karate from Alan Subishi from the Kyuukai (Secluded Ogre Association) Dojo located in an abandoned building.

Mizunuma is tall with glasses and smooth hair, not unlike Tanaka Tsutomu's style. Like Kenichi before his fight with Odin, Mizunuma was commonly seen in his school uniform during school, and at his dojo in Karate robes.

Also like Kenichi, Mizunuma is a shy person who was frequently bullied and stands up for his beliefs of righteousness by gaining strength and joining Shinpaku. In this, Mizunuma looks up to Kenichi as a role model. Unlike Kenichi, Mizunuma's sense of justice against enemies is not defensive, but offensive, as seen at one point when he attacked a middle school bully so badly that he caused serious injuries (and even hit Matsui in the face at one point).

His other role model is Alan Subishi, his master. When Alan was incapacitated by Yomi's Tirawit Koukin, Mizunuma was overcome with feelings of revenge and was first to step into the ring during the D of D tournament to advance Shinpaku so that he could fight Yomi.