"I'll give you some service as thanks for letting me crash at your place ♪" Living under the same roof with a slutty demon of a little sister! The protagonist of this game is an office worker who left home and started living alone in his apartment. One day, his sister who had gotten into a quarrel with their father and ran away from home, appears on his doorstep uninvited. It had been a while since they last met and so the protagonist is really surprised at her appearance: she has turned into a promiscuous blond-haired kogal! Getting irritated by his hopelessly selfish little sister, the protagonist is about to throw her out of the house, but her skilled sexy seductions coax him into following up on her request and allows her to stay. This marks the the beginning of their perverted life in cohabitation.