Kenji lives with his older brother & his wife, Mirei, and his younger brother & his wife, Mimi. As a matter of fact, Mirei and Mimi are sisters and their mother, Hitomi, also lives with them. His older brother is now abroad on business and his younger brother rarely comes back home. This means there are only Kenji and three women at home. One day, Kenji sees Mirei masturbating....