Kotaro is a 12 year old middle school classmate of Misaki, whom he has a crush on, as well as Hatoko's brother. He is always being assaulted by Tamayo and her various martial arts techniques, which he has been a victim of since he was four years old. He becomes jealous of Ohjiro's advances towards Misaki, going so far as to try to attempt to play a quasi-match of Angelic Layer against Ohjiro, despite the fact that he had never played it before. His family owns a karate dojo and Kotaro has practiced karate some himself, showing Misaki some of his knowledge in hopes that Misaki can use it to help Hikaru win.