SONE-626 "She's shy, timid, and weak to pressure" I was attracted to my girlfriend's sister, and I secretly had sex with her. I'm such a terrible person.

[The troubled face of the weak-willed Mita Marin is so cute it’s precious…] Marin is timid and timid. Although she is not aware of it, her appearance and mannerisms strike a chord with men, making her popular. She is assigned a tutor, Atsushi, her older sister’s boyfriend. He has a problem. Even though they have been dating for quite some time, Marin’s older sister is a very strict person and won’t let him have anything to do with her. Compared to her strong-willed sister, Marin seems weak and easy to get. Atsushi, whose desire was about to explode, made a move on his younger sister without thinking. But Marin… accepted. When Atsushi found out that she was weak-willed, his desire escalated more and more…