Yuki Touyama, a social outcast, has a secret that he hasn't told anyone. He is in a strictly sexual relationship with his classmate Yumi Takai. The two are not looking for mutual love, but rather treat each other as a convenient sexual partner.

One day, Marika Uehara, a popular girl in the class, sees Yuki buying condoms. Unexpectedly, Marika takes an interest in Yuki and starts to get involved with him during lunch break and after school. Yumi is confused, but at the same time, she is not completely satisfied with Yuki, and she begins to realize that she has a crush on him.

This is the start of a vivid, sweet and sour youth romantic comedy.