Emi, the student council president, is a quiet, beautiful, and perfect girl. Her younger sister, Ryuka, enjoys popularity comparable to that of an idol and is always the center of attention. Despite this, their younger brother Mizuki is rather ordinary.

Since childhood, Mizuki has been the target of teasing from Emi and treated demanding by Ryuka. However, his life takes a turn when he enters a romantic relationship. Nevertheless, his spring of love is disrupted when Ema, unable to accept her younger brother’s first love, takes off her clothes and sexually assaults him.

Emi enters into an inappropriate relationship with Mizuki, the student council president. Despite Emi telling Mizuki that they will only have sex once, Mizuki’s sexual desire knows no bounds. This desire is released at school, in the hallway, in the school storage room, anytime, anywhere, leading to her having sex without them realizing it. In addition, an important hidden secret comes to light, leading to a drastic change in the relationship between Emi and Mizuki.