[SONE-398] My girlfriend's innocent sister, who I'm sure will have sex with, missed the last train and came to stay with me. (Censored)

It was about a week ago that I had dinner with my girlfriend and her sister. "I missed the last train, can I come over now?" I suddenly got a call from her sister, who I had only met once. While I was unable to refuse, the intercom rang. Hana, who had arrived slightly drunk, stood very close, and her cleavage was exposed through the loungewear I had lent her. "I didn't tell my sister I was coming, you know? It's not like she'll find out." I could only see her every word and action as an invitation. Yes, yes, I can do it (gulp). 10 seconds left until we start our forbidden relationship...