"Oh! My sister's boyfriend, you were looking at my boobs, weren't you?" My first girlfriend's sister has super big boobs! Even though she has a girlfriend, she secretly shows off her estimated G-cup boobs and seduces me! "I'll tell her that I came inside her!" Even though my girlfriend is supposed to be important to me... I gave in to her temptation and she begged me even more, and my reason collapsed! My cheerful, charming, big-boobed sister completely took over the pace, and I secretly came inside her behind her back!