Natsuki has three brothers-in-law after her mother remarried. Everyone was kind and I felt like I had lived for a long time ... I even felt like that. Except for one person. Ken, the third son, was so conscious of Natsuki as the opposite sex, not as a family, that he stayed in his room and avoided Natsuki. Then, one day in the afternoon, Ken finally pushes Natsuki down. However, at this time, Natsuki did not know. That this was just the beginning of the collapse ...