Mitsuha, who lives a happy life with her kind boyfriend, gets a new stepbrother from her parents' remarriage... He is a rumored playboy senior at her boyfriend's part-time job. The day he attacks her and cums inside her while her parents are away, her happy daily life falls apart. Living under the same roof, she is transformed into a pussy tailored to her stepbrother's specifications. Gradually, she stops answering her boyfriend's phone calls and starts craving dick, giving him a blowjob. She becomes a sex-loving, orgasmic girl, and her body is unable to live without her stepbrother...