Yōjirō Mutsu is the third-year vice-captain of Shiro High School's men's rhythmic gymnastics team. Born in Tokyo, he relocated to Aomori—his mother's hometown—during childhood. There, he established an enduring friendship with team captain Tōru Takase, a bond persisting through their high school athletic endeavors. Mutsu maintains a courteous and tranquil exterior, often appearing amiable initially. This poised facade shifts to a daunting aura when his temper flares. His responsibilities include tempering Takase's volatile emotions and outbursts, serving as the team's stabilizing anchor during competitions and group dynamics. Mutsu regards rival Ao High School and its members as formidable opponents, respecting their capabilities and acknowledging their potential in tournaments like the inter-high competition.