When her husband is away on a business trip, her beloved older brother who lives at home suddenly comes to Tokyo. Natsuki, who is a closet girl, offers to let her use the spare room, and she takes him up on his offer. When she asks him why he came to Tokyo, he tells her that he broke up with his girlfriend over sex, and that he wanted to work at a brothel to hone his sex techniques. However, the brothel he had his eye on has quit, so the brother, at a loss, takes advantage of his sister's personality and offers to use her as a practice dummy. She can't refuse her beloved brother's request, and ends up accepting it.