Hiroki, a husband, lives a simple life in a small apartment with his pregnant wife Mari. As Mari's due date approaches, Mari's older sister Rio comes to stay with them for the time being to help with the housework. From the moment they meet, Hiroki is smitten with Rio's charms, his nose never stopping. Meanwhile, Mari suddenly goes into labor and is rushed to the hospital! The baby is born safely, and Hiroki and Rio celebrate at home. Drunk and losing their senses, the two find themselves at home without Mari...