After Natsuki's mother remarries, she suddenly has three adult stepbrothers. All of them are so kind that it soon feels as if they have always lived together—except for Ken. The third brother is so conscious of Natsuki as a woman rather than family that he hides in his room and avoids her. Then one afternoon, Ken finally pins Natsuki down. She has no idea that this is only the beginning of her family's collapse...