Kanae, the protagonist's younger sister, suddenly runs away from home and comes to live with him. Unable to forcefully send her away, the protagonist, Susumu, is captivated by his sister's fully grown, girlish body... Her large breasts, in particular, are enough to stir the protagonist's heart... "Hmm, if you really want it... how about 3,000 yen?" To earn some extra cash, his girlfriend suddenly begins a life of boob-shaming! Toying with his sister's breasts, he becomes a paid sex supporter, unleashing his desires!