When Natsuki's mother remarried, she had three stepbrothers. They were all kind, and it felt like they had been living together for a long time... except for one. The third son, Ken, was so conscious of Natsuki as a member of the opposite sex, rather than as a member of the family, that he would stay in his room and avoid her. Then, one afternoon, Ken finally pushed Natsuki down. However, Natsuki didn't know at the time that this was just the beginning of the breakdown...