I returned to my parents' house for the first time in a long while. My younger sister Yayoi and I were close when we were little, but we had been on bad terms since my rebellious phase. When I met her again after so long, she had grown up to be unusually sexy. But she still hasn't fully matured, as her panties were constantly showing...or were they showing...? The piece of fabric was digging into her crotch, unable to fully cover her big ass. There's no way I'd get turned on by someone like my sister...Then my parents went on a trip. Even when we were alone at my parents' house, her panties kept flashing. My sexual desire for my sister was unstoppable. Once I made a move, it was over, and we'd have sex and sex while our parents were out. My sister couldn't be this cute...she couldn't be this sexy...But even though I thought that, I kept doing it.