His wife Asako was pregnant and went back to her hometown, leaving her husband Tooru behind. Tooru was left behind and could barely do the housework, so the house was getting messier and messier. At that time, his wife's sister Nao came to help Tooru with the housework, worried about him... But Nao had actually come to relieve her sexual frustration with Tooru. Unaware of this, Tooru invited Nao into his home.