Another plot could be that Ash is turned into a battling beauty himself (in a magical or strange situation). He has to learn how to present himself and his Pokemon in a more aesthetically pleasing way while still maintaining his battling skills. This could involve him learning about Pokemon grooming, special moves for show, and how to walk his Pokemon in a way that impresses the judges.
Maybe Ash teams up with a battling beauty trainer. They could travel together and enter different contests where Ash focuses on the battling strategy against other trainers while the girl focuses on making her Pokemon look its best. Their combined efforts could lead to some interesting story developments, like dealing with jealous rivals who try to split them up.
One idea could be that Ash has to train a female Pokemon to enter a beauty contest that also has a battling aspect. He might face challenges in teaching the Pokemon moves that are both elegant for the beauty part and powerful for battling. For example, making a Pikachu do a cute electric display for the beauty show while also being able to use Thunderbolt effectively in a battle.