Meowth joining Ash in a fanfiction could also lead to some interesting character development for both. Ash might learn more about the Pokémon world from Meowth's perspective, especially the seedy side that Meowth has been a part of with Team Rocket. And Meowth could learn about friendship and loyalty in a new way, different from what he's experienced with Jessie and James.
If Meowth joins Ash in fanfiction, it could lead to some really interesting character dynamics. Meowth has been part of Team Rocket for a long time, so there would be a lot of room for him to change and grow. He could teach Ash some of the sneaky tricks he learned from Team Rocket, but in a more positive way. Maybe they'd form a new team and compete in different Pokémon competitions.
The storyline would likely become more complex. With Meowth around, there would be a new dynamic. His loyalty would be split between Ash and his old Team Rocket pals at first. This internal conflict could drive parts of the story.
In this fanfic, the plot could be that Meowth has a change of heart after an encounter with a powerful and kind Pokémon that Ash helps. This makes Meowth realize that Ash's way of treating Pokémon is better. So, he joins Ash. He could then use his unique skills, like his ability to talk, to help Ash in battles and communicate with other Pokémon more effectively.
His personality might become more positive. Instead of being a bit of a schemer like he was with Team Rocket, he could become more helpful and honest. He might start to care more about others' feelings.
One possible storyline could be that Meowth helps Ash find a rare Pokémon. Since Meowth has his own network among Pokémon, he might hear rumors about a very special Pokémon. He then takes Ash to the location, and they have an epic adventure trying to catch it. Another storyline could be that Meowth and Ash team up to take down a new evil organization that's causing trouble in the Pokémon world.
Ash joining Team Galactic in fanfiction could mean a complete shift in his character arc. He might be forced to do things against his will at first. But as time goes on, he could use his knowledge of Pokemon to gain an upper hand within the team. For example, he could use his bond with his Pokemon to resist the team's orders that are harmful to Pokemon.
Ash joining Team Rocket could lead to some interesting character dynamics. He might start to question his own values. For instance, he's always been about friendship with Pokemon, but Team Rocket is more about using them for gain. This internal conflict could be a major part of the fanfic. Also, his relationship with Jessie, James, and Meowth would change drastically.
In a fanfic, Meowth's evolution might be a result of a magical spell gone wrong. Instead of evolving into a normal form, it becomes a hybrid of different Pokemon types. This new form gives it strange and wonderful abilities, like being able to turn invisible or create illusions. But it also has to deal with the confusion of its new identity and how other Pokemon and humans react to it.
One possibility is that Ash joins Team Galactic under some sort of misunderstanding. Maybe he thinks they are a group with good intentions at first. Once he realizes their true nature, he has to figure out a way to escape or stop them. This could create a lot of tension and action - packed scenes in the fanfiction.
In a fanfiction where Ash joins Team Rocket, it could lead to some really interesting storylines. Ash has a lot of knowledge about Pokémon training that Team Rocket lacks. He could potentially teach them new techniques, but at the same time, his moral compass would be constantly at odds with their devious ways. Maybe he joins them because he's somehow tricked or he has his own secret plan to take them down from the inside. It would be a great opportunity to explore different aspects of his character and how he adapts to this new situation.