After forgetting to pack his bathing suit and before entering the water park, Keiichi wears a pair of trunks for three hours, containing the magical ability to make women attracted to whoever writes their name. Mion hears from her uncle that Keiichi wrote his name on the suit and he will fall in love by himself. After most failed attempts, the girls convince Tomitake, Oishi and Irie to remove the suit from Keiichi. While the three fight for the suit, the naked Keiichi refuses to wear the spare one.