Haruka Nanase and Rin Matsuoka are both gifted swimmers who are friends, but fierce rivals in the pool; their lives and the lives of their friends are chronicled as they compete alongside and against one another.
Haruka and the boys train hard to prepare for the showdown against Samezuka; after Day 1 of the tournament, Gou and Amakata-sensei treat the boys to a carb-rich feast and allow them to take a breather.
While Haruka and the boys redouble their training in the wake of prefecturals, Makoto notices Gou looking troubled and asks her what's wrong; she tells him that Coach Sasabe has been busy with his Swim Club lately.
At Samezuka Academy, the hot-blooded practices continue ahead of regionals; meanwhile, the Iwatobi Swim Club trains diligently each day until sundown; though Amakata-sensei is concerned, Haruka and the boys insist they want to practice.
As the tournament continues, Sousuke tells Rin about how he's past their years of separation; Rin is concerned at Sousuke's nonchalant attitude toward certain things and tries to speak his mind.