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.

Asahi tells his friends that he decided to be just friends with Yōko for now. Meanwhile, Nagisa reflects on how she brutally rejected Asahi the previous summer to prevent him from getting too close to her, but now acts jealous after seeing him with Yōko.

After discovering that UV rays from sunlight cause Yōko's skin to instantly tan, Nagisa decides to train her into dodging sunlight on her route to and from school.

After being relentlessly teased by Shiho's body in school, Asahi begins to projectile-nosebleed while Nagisa starts to get jealous.

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.

After the incident at the Summer Festival, Youko has been avoiding Asahi, unaware of how she really felt about the incident.

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.