Mizuki, who is about to take university entrance exams, went up to Tokyo to prepare for the tests and stayed at her sister's apartment for a while. Her sister, who continues to work even after marriage, can't keep up with her husband. Seeing this brother-in-law, Mizuki decided to use him as revenge for being dumped by her boyfriend. She performs fellatio next to her sleeping sister or forces sex when her sister is passed out drunk nearby. The two gradually start to feel stimulated by doing things they shouldn't behind the wife's (sister's) back…
