Asahi Kuromine, a high-school boy who has trouble keeping a secret from anyone, has a crush on his cool and reserved classmate Yōko Shiragami.

Now that it's summer, Asahi gets up the nerve to invite Yoko to the pool. The problem is, Yoko doesn't know how to swim and thinks that Asahi is asking her so they both could practice.

Asahi, Akari, Nagisa, Shiho and Akane pursue Youko, but are hampered by Akari's refusal to exceed the speed limit and risk damaging her new car.