Seijuro Mikoshiba

Captain of the Samezuka Academy Swim Club. Height: 187 cm, Weight: 77 kg. Hobbies include tennis, beach volleyball, and karaoke. He has a tough personality and is a young man with a strong spirit. He takes a liking to Gou after she visits the swim club looking for Rin and persistently pursues her.

His specialty is freestyle, and he has the skill to set new tournament records. In the first episode of the second season, he appoints Rin as the new captain and retires. Even after becoming a university student, he always comes to cheer during tournaments. He advances to Hidaka University on a sports scholarship and appears as a senior to Haruka and Asahi from the third season of the anime.