Haruka Nanase, a water enthusiast and swimmer at heart, once triumphed in a relay alongside his pals Rin Matsuoka, Nagisa Hazuki, and Makoto Tachibana during their elementary years. Following their victory, life led them on separate paths. Years later, destiny reunites them in high school, but Rin, focused solely on proving his swimming prowess over Haruka, harbors no nostalgia for the past. Undeterred, Haruka, Nagisa, and Makoto establish the Iwatobi High School Swim Club, setting their sights on a competition that demands a fourth member. With Nagisa's recruitment of Rei Ryuugazaki, a track team alumnus, the team is complete. As the tournament looms, the bonds between the four strengthen through rigorous training, aiming not only for victory but also to resolve the rivalry between Haruka and Rin once and for all.