Ash as the Chosen One in Pokemon fanfiction is a really interesting concept. It gives a whole new layer to his character. He could be given a special Pokemon by some mysterious force that is crucial for his destiny. This Pokemon might be one that no one has ever seen before. His friends would also play different roles, perhaps as protectors or guides to help him fulfill his chosen - one duties. And his battles would become even more epic as he has this greater responsibility on his shoulders.
His rival could be the one to betray him. Rivals are often jealous and competitive. If Ash's rival saw an opportunity to gain an advantage by betraying him, they might do it. For instance, they could lie about Ash to the Pokémon League, getting him disqualified from important battles.
I'm not sure specifically as there could be many different takes on it. Generally, it might be about Ash being some sort of chosen one in the Pokémon world. Maybe he has a special destiny, like being the only one who can stop an evil force or unlock a powerful Pokémon's true potential.
Ash is the main character for sure. Alongside him, his friends from the Pokémon world might also be significant characters. Brock and Misty could potentially be in it, continuing their adventures with Ash. Additionally, there could be some sort of Pokémon sage or elder who guides Ash on his path as the chosen one, providing him with wisdom and advice on how to use his special powers or face the upcoming challenges.
In this fanfiction, Gary could be an important character. Since he has always been in competition with Ash, he might have mixed feelings about Ash being the chosen one. Serena could also be a main character. She might be inspired by Ash's chosen - one journey and decide to follow him, offering her own skills and support. Professor Oak would likely be involved as well, guiding Ash with his vast knowledge of Pokémon.
One common theme is the struggle against gender expectations. Since Ash is now female in these fanfictions, she often has to deal with people underestimating her because of her gender. Another theme is the forging of unique relationships. With her new identity, the interactions with other characters, like her friends and rivals, can be different.
Ash is definitely one of the main characters since it's about him being the chosen one. His Pokémon partners like Pikachu are also likely to be main characters as they would be involved in his journey as the chosen one.
Another plot might involve Ash being transported to a different dimension where the rules of Pokémon battles are completely different. He has to quickly adapt and learn these new rules while also trying to find a way back home. In this dimension, his Pokémon might even gain new abilities or forms.
First, you need to define what it means for Ash to be the chosen one in your story. Is it a prophecy? A special power? Then, plan out his journey. Decide on the challenges he'll face, like powerful villains or difficult Pokémon to catch. You can also add new characters that are related to his chosen - one status. For example, a mentor who knows about the prophecy.
The concept of Ash as the chosen one is appealing because it gives his character a whole new level of importance. It's like he's not just a regular Pokémon trainer anymore but someone with a grand destiny.