Momo-san, who became my step-sister as the daughter of my father's remarried wife. She's the complete opposite of me, a recluse, and treats me brightly regardless of who I am. But because of her overly open personality, she lives defenselessly in front of me, who she doesn't treat as a man, in a thong that completely reveals her ass. I, who have never seen a raw ass before, continue to think of erotic things with my step-sister's ass, and one day, I reached my limit...