Yuu, a social misfit and NEET, stays at home and spends his days absorbed in playing erotic games. Yuu has Itsuka wanted to try out the erotic play he has developed through playing erotic games, so he decides to try it out on his cheeky little sister as an experiment. They compete in an erotic game, and the winner must do whatever the other person says, so they go head to head! Yuu wins by a landslide, and makes his big-breasted sister wear an obscene costume...