I live alone in Tokyo in a tiny apartment, and suddenly, I started living with my younger sister, Rika. Before I knew it, Rika's big boobs had grown so big that she was defenseless at home and always had them exposed, so I had nowhere to look! Unable to resist, I lost control and forced myself on her, even cumming inside her... But that night, Rika asked me for creampie sex, saying, "I've been horny for a long time too..." We entered into a secret relationship that we could never tell our parents about...