Nagi is devoting her days to lessons at a training school, hoping to become an idol. One day, her parents say they'll be away for a few days, leaving Nagi alone with her older brother, Yuzuru. Yuzuru is an otaku, and he sees his younger sister Nagi with special feelings that are different from the usual relationship between siblings, and engages in perverted acts with her, such as secretly taking pictures of her upskirts without Nagi noticing, and licking the rim of the juice she drinks, treating her as a sexual object. Taking advantage of their parents' absence, Yuzuru's perverted acts escalate... I'll seduce my little sister, an idol who's my very own flesh and blood, by developing her nipples and showing off my big cock.