Recently enrolled at Samezuka Academy, Sousuke Yamazaki reunites with his childhood friend Rin Matsuoka. The two reminisce about their past and express their desire to swim together once again. With the help of Captain Mikoshiba's younger brother Momotarou Mikoshiba and diligent Aiichirou Nitori, Rin and Sousuke form the Samezuka relay team and strengthen their bond. However, Sousuke's return seems to have an underlying reason that begins to affect his swimming and causes him distress. Rin notices these changes and encourages Sousuke to confront whatever is holding him back. As the team trains and participates in tournaments, the truth behind Sousuke's sudden return slowly surfaces.