His wife is going back to her hometown to give birth. Tomoya is about to go out to play pachinko, which is usually prohibited, to enjoy living alone for the first time in a while. Then, his wife's sister Mao comes over to help with the housework. He is grateful that she cleaned up the messy living room, but for some reason, he is suddenly exposed to her panties and breasts. His lower body reacts involuntarily to the intense sexiness that Mao exudes...