Since that unforgettable day five years ago, Nanami and I have become brother and sister due to our parents' remarriage...We've always been close, but when I see Nanami's breasts getting bigger and bigger as she grows, it makes sense. I feel like I'm going to lose it. So when my girlfriend's parents were on a trip overseas, she begged me to let her masturbate while sucking her breasts while I was on her lap.