My younger sister, Mei, was distressed by the sounds of AV coming from her brother's room. One day, Mei reunites with her childhood friend Mamoru. Mamoru is attracted to Mei's mature appearance. The distance between the two of them suddenly shrinks when they hear the AV sound coming from her brother's room next door. The sound of her brother watching an AV makes Mei horny, and she feels intensely having sex for the first time with her childhood friend.