Momo is my step-sister, the daughter of my father's new wife. She's the complete opposite of me, a shut-in, and is a cheerful person who treats everyone cheerfully. But because of my open personality, I wasn't treated like a man at home. She lives her life defenselessly with her thong completely visible. I'd never seen a bare butt before, but one day I reached my limit as I continued to think about my sister-in-law's ass in erotic ways...