Mukai asks company president Masahiko for financial help to save his subcontracting business, offering a marriage between his daughter Ai and Masahiko's only son, Naoto, in return. Masahiko, who has long desired Ai, agrees while secretly devising a plan. He bans premarital sex to leave Ai sexually frustrated, then sends Naoto and his own wife away on a supposed five-day business trip. Alone with his future daughter-in-law, Masahiko finally puts his long-awaited training scheme into action.