When he realizes he forgot to pack his bathing suit while rushing to meet his friends at the pool, Keiichi borrows a pair of trunks from Mion's uncle, who claims that these trunks have the magical ability to make women attracted to whoever writes their name on them and wears them for three hours. Mion hears from her uncle that he had made a mistake in describing the abilities of the trunks, and that the person whose name is written on the briefs will fall in love with the wearer, meaning Keiichi, who had written his own name on them, will fall in love with himself..