Shūsaku Shida coaches the men's rhythmic gymnastics team at Sōshūkan High School (Ao High School). A former ace gymnast from Hakumei University in Kanagawa, renowned for exceptional skills, a career-ending leg injury forced his retirement and catalyzed a profound personal change. Pre-injury arrogance gave way to patience and reflection. During rehabilitation in Germany, he met nurse Rei Shida, who became his wife. Their relationship remains private; only Shūsaku and his relative, team manager Asawo Kurikoma, have directly interacted with Rei, who never appears before the team.

Shūsaku possesses mid-length light ash blonde hair and distinctive lavender eyes. Casually, he favors a white dress shirt under an iris-purple cardigan, black formal trousers secured by a brown belt with a silver buckle, and brown formal shoes. For coaching, he wears a grey tracksuit jacket with a black front, matching grey trousers, and sneakers.

As coach, Shūsaku embodies cheerfulness, kindness, and altruism. He prioritizes the team's enjoyment of rhythmic gymnastics and personal growth over competitive results, emphasizing collective experience. His coaching philosophy is deeply influenced by his wife Rei's perspective; he frequently references her advice, especially when guiding captain Masamune Shichigahama, using her words to underscore teamwork and perseverance. His own impressive backflips initially inspired several members, including Shichigahama, to pursue the sport.

His surname "Shida" combines the kanji for "will, purpose" (志) and "field, rice paddy" (田), while "Shūsaku" means "excellent, circumference" (周) and "make, production" (作). Across all official media, including the television series and subsequent anime film, Shūsaku consistently mentors the team, guiding them toward competitions while drawing on his past experiences and personal values.