Kentaro Yamanaka is the ace pitcher for Bunan High School, renowned for leading his team to a championship victory at the Kōshien national baseball tournament. His longstanding connection to Yuri Nakao—daughter of Seishū High School's baseball coach—originates from their childhood as neighbors and a period when her father coached him. This history fuels his recurring presence among the central characters.

After unexpectedly reuniting with Yuri, Kentaro positions himself as a romantic rival to Katsuya Niimi, a key Seishū player pursuing a relationship with her. He occasionally leverages familial ties, notably through his younger sister Chimi Yamanaka, to complicate Yuri and Katsuya's dynamic. His younger brother Jirō Yamanaka further intertwines their worlds as a new third baseman for Seishū's baseball team. Kentaro's role remains defined by these core relationships and his identity as a skilled competitor.