The story would likely become more about Ash's internal struggle. As a Pokémon, he'd view the world from a different perspective. His goals might shift from winning badges to something more related to Pokémon survival or acceptance. For instance, he may strive to prove that Pokémon with human - like intelligence deserve better treatment.
In this fanfiction, the power dynamics would be different. Ash, as a Pokémon, would no longer be in the position of a trainer. He'd have to rely on his natural Pokémon abilities and instincts. This could lead to him forming alliances with Pokémon that he previously would have caught. The story could also explore how his Pokémon friends from before react to his transformation. Do they still see him as their trainer or as an equal now?
Some of his Pokémon like Pikachu might be very protective. Pikachu would stay close to Ash at all times, being extra vigilant in case any danger comes while Ash is in this new form. It would also be curious and might try to play with Ash's new fairy features, like his wings if he has any.
If Ash was secretly a Pokémon, trainers might view Pokémon in a whole new light. They would see that Pokémon could be more like them, with complex emotions and motives. Also, Ash's relationships with other Pokémon and trainers would be re - evaluated. His Pokémon friends might see him as an equal rather than just a trainer.
His relationship could change in terms of training. Ash might start to incorporate some of Giovanni's more strategic training methods (assuming he learns about them). However, his Pokémon might be resistant at first, as they are used to Ash's traditional and more friendly training style. But over time, they could adapt and become even stronger. Also, Ash's Pokémon might have to deal with new rivals associated with Giovanni, which would test their loyalty and determination to stay with Ash.
His Pokémon might be really confused at first. They're used to Ash as a human, so seeing him as a Pikachu would be quite a shock. But some of them, like Pikachu himself, might feel a closer bond since Ash is now in a similar form.
Ash would probably become more patient. Rangers often have to wait and observe Pokémon in their natural habitats. This is different from his Trainer days where he was more focused on quick battles and leveling up his Pokémon. He'd also be more diplomatic, since he'd need to work with other Rangers and people in the Pokémon world who might have different opinions on conservation and Pokémon management.
It would change it a great deal. He'd be able to protect his Pokémon better. For instance, if they were in danger from a powerful enemy, he could use the Force to shield them.
Well, he could have all sorts of wild adventures that deviate from the original story. Maybe he'd be a different type of Pokémon trainer, like one who specializes in psychic Pokémon instead of his usual variety. He could also form new relationships with other characters, both human and Pokémon, in ways that the original anime didn't explore.
At first, his Pokémon would be startled. They've always known Ash as a human. But then, they would start to adapt. Some Pokémon, like Squirtle, might try to play with Ash in his new form, thinking it's a new kind of game. However, his more loyal Pokémon, like Greninja, would be determined to find a way to turn Ash back. Greninja might use its special bond with Ash to try and communicate with him on a deeper level in this new form, to understand what happened and how to reverse it.
Ash's personality could become more diplomatic as a girl. In the Pokémon world, he would need to navigate different social situations. As a girl, he might use charm and persuasion more often. His love for Pokémon would still be there, but he could show it in a more gentle way. For example, instead of just being excited about catching new Pokémon, he might focus more on the well - being and happiness of the Pokémon he already has.
Their relationship with other Pokémon would likely change quite a bit. For Ash, his other Pokémon like Charizard might initially be a bit aloof towards Plusle and Minun. But as they see how useful Plusle and Minun can be in battles and how they contribute to the team spirit, they would warm up to them. For May, her Pokémon like Eevee could start to develop new strategies in battles with the addition of Plusle and Minun. Plusle and Minun's presence could also encourage Ash and May's other Pokémon to be more social, as they are very social Pokémon themselves. This could lead to more group activities among all of Ash and May's Pokémon, like playing games together or exploring new areas as a united group.