A fashion - savvy character might be introduced who helps Ash perfect his girl disguise. This character could be from a big city and have a lot of knowledge about the latest Pokemon trainer fashion trends. They could also have their own set of Pokemon with unique abilities that they share with Ash during his time in disguise.
There could be a female trainer who becomes Ash's rival while he's disguised as a girl. She might be initially dismissive of him, thinking he's just another girl trying to make it in the Pokemon world, but later be surprised when she discovers his true identity.
Perhaps a mysterious Pokemon that is only attracted to female trainers shows up. This Pokemon could play a key role in the story as Ash, in his girl disguise, tries to befriend it and use it to his advantage in battles or quests.
There could be a new rival for Ash. This rival might have a very different approach to Pokemon training, like focusing more on the beauty and grace of Pokemon rather than just battle strength.
There could be a lone traveler who Ash meets while he is alone. This traveler might have a unique way of training Pokemon that Ash has never seen before and could teach him some new tricks.
There could be a new trainer who has a very different style of training Pokémon compared to Ash. Maybe a young girl who uses music to communicate with her Pokémon. Another potential character could be an old Pokémon sage who has a vast knowledge of ancient Pokémon lore and can offer Ash some valuable advice on his journey.
Potential characters might include a new group of Pokémon thieves that Ash has to deal with. Also, there could be a local Pokémon healer who becomes an important part of the story. There might be some young Pokémon enthusiasts who look up to Ash and join him on his adventures. Another possibility is a reclusive Pokémon trainer who has some rare Pokémon and Ash tries to learn from them.
There could be a female mentor who takes Ash under her wing because she sees potential in her as a girl in a male - dominated world. This mentor could teach her unique skills and ways of dealing with Pokémon. Another potential new character could be a rival who is also a girl and has a different view on how to compete in the Pokémon world compared to Ash. They could have some interesting battles and exchanges of ideas.
There might be a young and inexperienced trainer who is lost. Ash, being the more experienced one, decides to help the trainer find their way. This new character could look up to Ash and in the process, Ash learns more about himself as a role model. It would be an interesting dynamic as Ash is usually the one being guided by his friends.
Obviously, Ash would be the main character. His Pikachu would also play a major role as always. Then there could be Professor Oak, who might help Ash understand his new identity. Also, Gary Oak could be involved, maybe as a rival who is initially skeptical of Ash's new - found status.
Obviously, Ash and Pikachu are the main ones. But we could also see Misty and Brock, Ash's old friends from the beginning of his journey. Maybe Gary too, as he has been Ash's rival for a long time.
One potential side character could be Cilan. He could come and visit Ash and Dawn, bringing new recipes and ideas for Pokemon food. Dawn's friends from the Pokemon contests, like Zoey, could also be side characters. They might come to visit and share stories of their recent contest experiences. And then there's Ash's mother. She would be overjoyed at their marriage and could be constantly checking in on them, bringing home - made treats for them and their Pokemon.
Another plot could be that Ash's friends don't recognize him when he's dressed as a girl at first. This leads to some comical misunderstandings and situations, like his friends trying to flirt with him thinking he's a new girl trainer, while Ash is desperately trying to give them hints without blowing his cover.