My girlfriend was away and secretly fucked her premature ejaculation sister who seemed weak to pushing her, 7 days of living together

Exclusive third installment! Ichinomiya Kiho's first attempt at a drama! My house has stopped running at my gas and the electricity and gas has stopped, so I'll stay at her house. She has a younger sister, and it's the first time I've seen her... but she seems to be on guard for me. That night, her girlfriend refused to have sex, and while she was masturbating, she was left with her sister! My younger sister seems to be weak to pushing, so maybe she's going to do this... It's been a week since I secretly fucked her with her without telling her. My little sister's temptation gradually escalates...