Gary could be one of his rivals. Gary has always been competitive with Ash. Another potential rival could be a new character introduced in the fanfiction, someone who is really good at Pokemon battles and wants to prove himself better than Ash.
One potential rival could be a male trainer who has a more traditional view of Pokémon training and looks down on the fem Ash's different approach. He might constantly try to one - up her in battles.
In Kalos, one potential rival for Ash could be a local trainer who specializes in Fairy - type Pokémon. Fairy - type Pokémon can be quite tricky in battles, and this trainer has mastered the use of their unique abilities. For Misty, a rival could be a girl who is an expert in water - type Pokémon battles, just like Misty herself. This girl might have some rare water - type Pokémon from Kalos that Misty has never seen before.
There are quite a few potential rivals. For example, Paul could be one. He has his own unique battling style and might be intrigued by Ash's Alola - champion ways. Then there's Trip. He could see Ash as a target to boost his own reputation. And in Alola itself, some of the more ambitious students from the Pokémon school who are aiming to be the best might also become rivals, constantly challenging Ash to prove they are worthy.
Some potential rivals could be the local Unova trainers who are known for their unique battling styles. For example, a trainer who specializes in using Bug - type Pokemon could be a tough rival for them.
Well, the story could start with Ash arriving at the Pokemon school. The school could be in a new region, filled with Pokemon that Ash has never seen before. He quickly realizes that the teaching methods are different from what he's used to. There could be a strict headmaster who initially doubts Ash's abilities because of his unorthodox way of training. But as time goes on, Ash proves himself by using his unique bond with his Pokemon. He could also participate in school tournaments, where he showcases his skills and strategies, and along the way, he might even inspire other students to think outside the box when it comes to Pokemon training.
Perhaps he defeats some of the Elite Four members who are participating in the league. They are known for their strength, so it would be a huge accomplishment. And of course, any recurring rivals from his past adventures like Trip or Paul.
In the fanfiction where Ash goes to the Pokemon Battle Club School, it would be an amazing place. There could be different classes for different types of Pokemon battles, like one for water - type battles and another for fire - type. Ash would be so into it, trying to soak up all the knowledge. He might even get the chance to teach some of his own battle experiences to the other students. And of course, there would be epic battles between students, with Ash right in the middle of the action.
One possible fanfiction could be that Ash starts at the Pokemon Trainer School feeling a bit out of place. He's used to learning on the go in the wild. But at school, he meets new friends who teach him different strategies for battles. He might struggle with the classroom setting at first, like having to sit still and listen to lectures about Pokemon types. However, his real - world experience gives him an edge when it comes to practical training sessions.
Ash might meet a strict teacher who has no idea about Pokémon at first but gradually becomes interested in them. He could also meet a rival in school who challenges him not only in academics but also in Pokémon battles.
Lillie is a likely character. She could befriend Ash and they might go on Pokémon adventures together. She has her own story and growth in the Alola region, and interacting with Ash could add more depth to both of their characters. Also, Ash might meet the Trial Captains like Mallow or Sophocles. They could challenge Ash in different ways and teach him about the island challenges.