As the Iwatobi High School Swim Club enters its second year with no new recruits, senior students Haruka Nanase and Makoto Tachibana, along with their friends Nagisa Hazuki and Rei Ryuugazaki, face the challenge of attracting new members to prevent the club's closure. Meanwhile, with graduation looming, Haruka and Makoto are at a crossroads, uncertain about their future careers unlike their ambitious friend Rin Matsuoka, now leading Samezuka Academy Swim Club. The arrival of Sousuke Yamazaki, a new swimmer at Samezuka Academy and an old acquaintance of Rin, adds a layer of tension to their dynamic, sparking conflicts among the trio.