Ryuta Seki is a first-year student at Noukin High School who joins the kabaddi club after his classmate Nobutaka Ban invites him following a practice match against Souwa High School. He has a background in junior high sumo wrestling, contributing to his physical capabilities despite his chubby build and preference for wearing glasses.

Physically, Ryuta has black hair and blue eyes. He wears the red Noukin High kabaddi uniform with the number 8. His build and sumo experience provide a foundation for adapting to kabaddi's physical demands.

Ryuta demonstrates high communicative competence and social skills. He maintains long-term childhood friendships with Nobutaka Ban and Yuki Hitomi, which facilitate group cohesion. His sociable nature extends to the kabaddi team, where he actively plans group activities to strengthen team bonds. For example, in Episode 8, he organizes a bowling outing, unexpectedly revealing advanced bowling skills through specialized equipment and high scores, showcasing his role in fostering camaraderie and surprising teammates with hidden talents.

His development centers on integrating into the kabaddi environment and his supportive role. He joins alongside Ban and Hitomi, inspired by the effort displayed during kabaddi matches.