Sumire nee-san returns home to her family's house after breaking up with her boyfriend, suddenly coming back with her usual spoiled and selfish attitude that somehow feels nostalgic. When I go to call her from her old room, I find her relaxing and deeply engrossed in masturbation, playing with her own nipples. I hear moans I've never heard before, making my cock naturally harden. After she catches me peeking, from that day on I become obsessed with my sister's nipples. A summer of intense closeness begins, drawing me deeper into a relationship that feels like incest, where she finally lets me fuck her.