Shūji Mabuchi coaches the men's rhythmic gymnastics club at Hakumei University Affiliated High School, commonly called Shiro High. Hailing from Aomori Prefecture, he employs an enthusiastic yet strict coaching style, rigorously drilling club members with disciplined guidance.

He shares a deep, longstanding friendship with Shusaku Shida, coach of rival Ao High School. Together, they laid the foundation for the Hakumei University men's rhythmic gymnastics team in their youth. Mabuchi served as team captain during Shida's competitive years at Hakumei, and he firmly believes Shida possessed the potential to elevate men's rhythmic gymnastics to Olympic status before a career-ending leg injury forced his retirement. Mabuchi was a consistent source of support for Shida throughout his recovery.

Mabuchi regards Ao High School and its team as worthy rivals, a perspective rooted in his history with Shida. His coaching philosophy centers on rigorous discipline, reflecting his commitment to developing skilled gymnasts at Shiro High. Physically, he has short black hair and black eyes, typically seen in a black tracksuit jacket featuring yellow accents on the collar, wrists, and hem, worn over a white t-shirt, paired with black tracksuit trousers, and white-and-red sneakers.