Yuu, a social misfit and NEET, stays at home and spends his days absorbed in eroge. He had always wanted to try out the erotic play he had developed through eroge, so he decided to try it out on his cheeky little sister as an experiment. They competed in an eroge game, and the winner had to do whatever the other person said in the penalty game. Yuu won by a landslide, and made his big-breasted sister wear an obscene costume...