Haruka Nanase possesses a deep affection for water and a fervent passion for swimming. During elementary school, he participated in and secured victory in a relay race alongside his three friends: Rin Matsuoka, Nagisa Hazuki, and Makoto Tachibana. Following their triumph at the tournament, the quartet parted ways. Years later, they reconvene as high school students; yet, Rin remains indifferent to restoring their past dynamic. He not only attends a different school but is singularly focused on demonstrating that he is a superior swimmer to Haruka. Following this acrimonious reunion, Haruka, Nagisa, and Makoto resolve to establish the Iwatobi High School Swim Club, though they require a fourth member to qualify for the forthcoming tournament. Rei Ryuugazaki, a former track team athlete recruited by Nagisa, joins them. As competition day approaches, the four forge a tight bond through rigorous training, aiming to achieve victory and finally resolve the rivalry between Haruka and Rin.