Manabu, a student who is studying for entrance exams and lives with his parents, is engrossed in a popular exploration-type monster collecting game and wanders around the neighborhood. One day, he is led by the game to a vacant house that has rarely been visited since ancient times, and notices a woman's voice coming from the back room. When he timidly peeks in, he finds Yuka, a married woman who his parents are close to, writhing in lewdness that is hard to imagine from her usual quiet and pure appearance...