Shūsaku Shida coaches the Sōshūkan High School boys' rhythmic gymnastics team. Once an elite gymnast and the ace of Hakumei University's team, he possessed talent considered capable of elevating men's rhythmic gymnastics to the Olympic stage. A severe leg injury abruptly ended his competitive career. This injury required medical treatment in Germany, involving surgery and rehabilitation. During his recovery, he met a nurse named Rei; her advice profoundly changed his outlook, transforming him from an arrogant athlete into a patient and encouraging mentor. Rei later became his wife. Struggling to find purpose after retiring from competition, Shida was helped by his university senior, Shūji Mabuchi, who secured him the coaching position.

His coaching philosophy emphasizes teamwork, personal growth, and finding joy in the sport. He frequently shares advice originating from his wife, though her existence remained unknown to his team until their interactions in Germany were revealed. His own past as an athlete allows him to deeply empathize with his students' challenges, particularly in fostering camaraderie among individuals with distinct personalities.

He is related to the team's manager, Asawo Kurikoma, who has known him since childhood and assists with technical aspects like video analysis and costume design. Shida's recruitment efforts were crucial in forming Sōshūkan's team, most notably inspiring the captain, Masamune Shichigahama, to pursue gymnastics after witnessing his backflips.

Shida has mid-length ash-blond hair and distinctive lavender eyes. He typically wears a white dress shirt with a purple cardigan, formal black pants, and brown shoes, while his athletic wear is a grey tracksuit. Born in Kanagawa Prefecture, his surname "Shida" (志田) combines the characters for "will" and "field", and his given name "Shūsaku" (周作) means "circumference" and "make".