The gravure idol I use as masturbation material every day suddenly appears in front of me—and I discover she is my adult girlfriend's sister, Marina Yakuno. Her revealing swimsuit and natural 92-centimeter H-cup breasts snap my self-control. Even with my girlfriend nearby, I cannot stop squeezing, sucking, and burying myself in those soft tits while pounding Marina in a sweaty frenzy. I finally cum with a shameless apology to my girlfriend.