Ataru is left alone at home while his parents go on a three-day, two-night trip together, which he won in a lottery. An acquaintance of his mother comes to help with the housework and cooking, but the person who turns out to be Yuna, a sexy woman who is hard to believe is an acquaintance of his plain mother. At first glance, Ataru is captivated by her beauty and schemes to get her to stay at home. And so begins a long, erotic night alone with Ataru and Yuna.