While his wife is away on business, ordinary salaryman Seiji Yusa hears a clap of thunder followed by a knock on the door. His daughter Mayu and her best friend Rena were caught in the rainstorm and are soaked to the bone. Mayu goes to take the first bath, leaving him alone with her provocatively dressed friend.

Rena is a virgin, but has always had a crush on Seiji. When the power goes out, Rena decides to make her move on the married man.