Suzushiro Ryou works as a teacher in an all-girls school.
Saori, Ryou's little sister is famous for being the perfect honor student, or so that is what everyone thinks.

But, Ryou knows Saori's true hidden face very well.
Every time something happens to put her in a bad mood, she teases Ryou, forcing him to do all kind of sexual acts.

One day, Ryou receives a love confession by a fellow female teacher.
Saori overhears this and since then, the teasing and sexual acts begin to escalate further and further.

"I won't hand over Onii-chan to that woman" Saori says.​