Eiken Asuka coaches the boys' soccer team at Warabi Seinan High School, characterized by his broad, muscular frame, tan skin, and short black hair. His eyes remain typically closed but appear black when open.

Asuka's coaching philosophy exclusively prioritizes physical strength as soccer's fundamental element, driving him to enforce rigorous physical conditioning for his players. He maintains an uncompromising personal fitness routine with daily gym sessions and pushes his team to focus relentlessly on strength-building year-round.

When the girls' soccer team requests joint practice sessions, Asuka rejects the proposal, viewing no strategic advantage for his squad. The girls attempt to blackmail him into compliance, but their efforts fail. He concedes only after the girls' team advisor, Gōro Fukatsu, successfully blackmails him into permitting the joint practices.