A teenage girl attending an idol training school was trained for three days in advance, while her parents were away, to become obsessed with nipples and large penises. (Yasaka Nagi, MIDA-382)

Nagi dedicates herself to becoming an idol, diligently attending training classes. One day, her parents say they're leaving home for a few days, leaving only her and her brother Yuzu at home. Yuzu is an otaku who harbors special feelings for his sister Nagi that differ from typical sibling affection. He engages in perverse acts such as secretly filming under her skirt and licking the rim of her juice cup, treating her as a sexual object. While their parents are away, Yuzu's perverse behavior escalates... Nipple development and penis attraction have led me to become my flesh-colored masturbation idol sister.