Kobayashi was captivated by that sight at first glance. On this day when he came to his friend's house to play, Kobayashi witnesses his friend's mother, Chisato, in her underwear in the bathroom. She's beautiful, but her underwear is tacky... Big pants that only seek functionality and have nothing to do with fashion. But for Kobayashi, a virgin who had fantasies about women, it was the first time he had seen a real woman's figure. Since then, Kobayashi began to steal Chisato's underwear whenever he had the chance. And before he knew it, he came to think that there was no one else to offer his virginity to but Chisato.