A year has passed since the Iwatobi High School Swim Club was established, yet no new members have joined. With Haruka Nanase and Makoto Tachibana now seniors, alongside their younger friends Nagisa Hazuki and Rei Ryuugazaki, they must find a way to recruit new members. Otherwise, the club will be forced to close the following year due to insufficient membership. Meanwhile, with graduation approaching, the seniors must also decide on their future plans. Unlike their friend Rin Matsuoka, the new captain of the Samezuka Academy Swim Club who is determined to fulfill his dream of becoming a professional swimmer, Haruka and Makoto are unsure about which career path to pursue. Further complications arise when Rin's old friend, Sousuke Yamazaki, comes to the city to study at Samezuka Academy; the arrival of the recently scouted swimmer creates tension in the relationship among him, Rin, and Haruka.