While my girlfriend was away, I secretly had sex with her younger sister, who has premature ejaculation and is bad at saying no, for seven days while we lived together. (Ichinomiya Nozomi MIDV-204)

My electricity and gas were out, so I stayed at my girlfriend's house temporarily. My girlfriend has a younger sister, and it was the first time I'd seen her… but she seemed very wary of me. That night, my girlfriend refused to have sex, and while she was masturbating, her younger sister secretly watched her. She seemed like an easy target, someone I could… so I secretly spent a week having sex with her, hiding it from my girlfriend. Later, the younger sister's advances gradually intensified…