After fighting with her boyfriend, Mami, the younger sister, ends up at her older sister's house and encounters her older sister's boyfriend for the first time. When she teases her older sister's boyfriend, who seems shy and serious, with a mischievous spirit, it ignites his sexual desire, and from that day on, he starts asking for more sex. It turns out that he has a premature ejaculation penis that keeps coming back no matter how many times he ejaculates, and he fucks her so hard that she regrets it, with pistons that break her pussy!