Third exclusive work! First challenge to a Kiho Ichimiya drama! My house had its electricity and gas shut off, so I ended up staying at my girlfriend's house. She has a younger sister, and this is the first time I've met her... she seems to be wary of me. That night, I was rejected for sex by her, and while masturbating, I was caught peeking at by her younger sister! Because she seems to be weak to pressure, maybe I can do this... A week of secretly fucking her younger sister without her knowing. The younger sister's temptation gradually escalated...