The first part of the series features big sister Amami Mao, the perfect woman and the class president. And she just cannot get enough sex. We also meet Musou's cousin, Hanamaki Arisu, whose goal is getting the male student to quit school by harassing them.

The story starts with his sister and their teacher who instructs Musou to give his "special medicine" to help calm her down. It is not long before the principal (his aunt) asks him to come to her office threatening to expel him for all his lewd acts, but before long someone comes to help…