Wataru, who is infatuated with Isumi, challenges Hayate, whom he perceives as a rival, to a duel. Hayate loses to Wataru on purpose, hoping for a romantic conclusion between Wataru and Isumi that will allow Nagi to break off her unwanted engagement. However, his overly obvious act ends up hurting Wataru's feelings. In order to reach Wataru and apologize, Hayate, together with Isumi and Nagi, must brave the Tokyo subway system.