Isuzu Mikoshiba serves as captain of the competitive swim team at Hidaka University High School in Tokyo. Her move to this school, distant from her hometown, stems from Hidaka's renowned swim program. She is the younger sister of Seijuro Mikoshiba and the older sister of Momotaro Mikoshiba, sharing a loving bond with both brothers. Isuzu possesses a vivacious and fiercely competitive personality. She confidently asserts her athletic prowess, notably challenging Haruka Nanase to a race immediately upon meeting him. She bonds quickly with Gou Matsuoka over their shared appreciation for muscular physiques. Outside the pool, she enjoys playing video games. Physically, Isuzu has an average height and a well-toned physique. Her features include amber-colored eyes and russet hair cut bluntly to chin length. She frequently wears a green jacket with orange piping or a standard competition swimsuit, sometimes accessorizing with a baseball cap. As captain, she leads team training and manages Hidaka swim team dynamics. Her documented story centers on her leadership role, family relationships, and interactions within the swim team environment.