Takeshi Kawai emerges as a supporting character, established as a regional boxing champion in Japan. He masters the upper jab technique, deploying deceptive tactics and psychological manipulation within the ring. A background in piano training informs his boxing style, integrating that discipline's precision. Takeshi is known to employ underhanded strategies to secure advantages during bouts.

He enters the national junior boxing tournament, the Champion Carnival, facing elite fighters including Ryuuji Takane. Post-tournament, Takeshi joins Team Japan alongside Ryuuji, Jun Kenzaki, Ishimatsu Katori, and Kazuki Shinatora. This team confronts international challengers, notably Black Shaft's American team, where Takeshi participates in matches showcasing Japan's boxing strength. His development centers on refining technical skills within the team dynamic during these international competitions.