Slayers (1995) : 3x17

Amelia and Gourry finds out that one of the fish-girl, Lila, is in love with a human, Kerel, when she saved him from a ship wreck. The father of the girl, Honar, objects at first, but their love is stronger. Their is an ancient spell that could change her into human. The only thing is, they need a beautiful young woman to get the stone off a sea creature from. Yes, Gourry is in drag, and they manage to get the jewel of the sea creatures head. When they try to do the spell, it doesn't work. The father feared this might of happen, and reveals they would have to kiss each other to prove their love. This would then transform them oppose each other (she human, he fish) to prove they actually love each other. Of course, they kiss and each other turns shape.