miru, the stepsister, is a legendary nymphomaniac rumored to pick up men anywhere in the city and dive headfirst into sex. Arrogant and sharp-tongued, she constantly mocks me, her older brother, calling me "uncool," "boring," and "cherry boy." Yet slowly, I begin to find pleasure in being teased by her. One day, while flipping through a porn magazine and jerking off in the living room, I'm suddenly caught by my sister—my erect cock exposed. Fearing her usual ridicule, I brace myself, but she surprises me by saying, "Hey, you're actually packing a decent dick when hard." Then, without missing a beat, she adds, "Never been touched before? How about I take your virginity?" In no time, I'm plunged into an overwhelming first experience—orgasm denial, nipple teasing, countdown ejaculation—far too intense for a virgin. After crossing that line, our relationship changes completely. Morning blowjob sessions, hidden sex in the kitchen, and fucking in a yukata after the festival—sex now invades every corner of daily life. Dominated by this mischievous little sister, I'm at her mercy around the clock.