The story revolves around Haruka Nanase, a boy who has always loved diving into the water and swimming. Before graduating from elementary school, he participated in a swimming tournament with other members of the swim club, Makoto Tachibana, Nagisa Hazuki, and Rin Matsuoka. After achieving victory, each of the children went their separate ways. Time has passed, and in the midst of their uneventful high school lives, Rin appears and challenges Haruka to a match, where Haruka demonstrates his overwhelming strength. Not wanting it to end this way, Haruka gathers Makoto and Nagisa once again and forms the Iwatobi High School Swim Club, convincing a new member named Rei Ryugazaki to join them in their goal to defeat Rin.