One possible plot could be that Ash, as a female, has to face different challenges in the Pokémon world. For example, some trainers might underestimate her at first. But she uses her knowledge and skills to prove them wrong. She might also form different relationships with her Pokémon. Maybe her Pikachu would be even more protective of her in this new form. And she could have unique adventures that are different from her male self's, like being more involved in Pokémon contests due to the perception that female trainers are more into that aspect of the Pokémon world.
In this fanfiction, Ash as a female could have a plot where she tries to break the gender stereotypes in the Pokémon universe. She might encounter other female trainers who have been held back by traditional views. Ash could then inspire them to be more adventurous and competitive. Her transformation could also lead to a change in her team dynamics. For instance, she might attract different types of Pokémon that are more drawn to her new female energy. This could open up new storylines such as training and evolving Pokémon that she wouldn't have had access to before.
One possible plot could be that Ash is turned into a Pikachu by a strange spell cast by a mischievous Pokémon. As a Pikachu, he has to figure out how to communicate with his friends. His Pokémon pals at first don't recognize him, but Pikachu - Ash starts using his old battle strategies in a new way. For example, he tries to direct Pikachu's electric attacks in the same patterns he used to direct his other Pokémon's moves in battles. Eventually, his friends realize it's him and they set out to find a way to reverse the spell.
The plot might involve Ash being cursed to turn into a fairy. He then has to go on a journey to find a way to reverse it. Along the way, he meets other fairy - type Pokémon and fairies who either help or hinder him. He could learn about the fairy world's culture and traditions, and this knowledge could be the key to breaking the curse. Maybe he has to prove himself worthy in some way, like by helping the fairies solve a big problem in their realm.
One possible plot could be that Ash wakes up one day as a girl and has to deal with all the changes in his daily Pokémon adventures. For example, he might have to adapt to new clothing styles and different social interactions. His Pokémon might also react in various ways to his new form.
One idea could be that a powerful magic spell backfires on Ash. His friends then have to take care of baby Ash while trying to find a way to reverse the spell. They might face challenges like getting baby Ash to eat Pokémon food or stop him from toddling towards dangerous Pokémon.
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.
It could be Team Rocket as always. Since Ash is now a Pikachu, they might see it as an easy target to capture. They could have new gadgets specifically designed to catch Pikachu - Ash, and constantly try to get their hands on him throughout the fanfiction.
One possible plot could be that Ash encounters a female Lugia in a new and unexplored region. The Lugia is in trouble, perhaps being hunted by an evil organization. Ash decides to help it, and in the process, they form a unique bond. They go on adventures together, with Ash learning new things about Lugia's powers and how to communicate with it better.
One possible plot could be that Ash discovers a female Mewtwo in a hidden location. She's scared and alone, and Ash decides to help her. They form a bond and go on adventures together, facing various Pokémon trainers and challenges along the way.
Well, one possible plot could be that her friends have to take care of her as a baby. Harry and Ron might struggle to figure out how to keep her safe and fed. They could search for a way to reverse the spell that turned her into a baby.
Well, perhaps the plot could involve the other characters having to take care of baby Kagome. Inuyasha might be really confused at first but then grow protective. Sango and Miroku could help out too, trying to figure out how to turn her back while also making sure she's safe and healthy.