Meowth's personality could change in several ways. He would likely become more trusting. In Team Rocket, he was often on guard. But with Ash, he could let his guard down. Also, he might become more selfless. He was used to thinking about himself and Team Rocket's goals before. Now, he could start thinking about the well - being of Ash's whole team. For example, he could offer to share his food or resources with the other Pokémon in Ash's group without hesitation.
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.
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.
If Ash were to turn into a Pokemon in a fanfic, his personality would surely be affected. He's used to being in control as a trainer, but as a Pokemon, he'd have to learn to follow others' commands or work within a group. His once outgoing and friendly nature might become more cautious. He'd have to be more aware of predators and threats. And his competitive spirit might take on a different form. Instead of competing in trainer battles, he'd be competing in Pokemon - on - Pokemon battles, which could make him more aggressive or strategic depending on the Pokemon he turns into.
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.
Pikachu would likely be very confused and resistant. Pikachu has a strong bond with Ash and knows his true nature. It would probably try to shock Ash out of whatever trance or false belief he has from joining Team Galactic. For example, when Ash starts to follow Team Galactic's orders that go against his usual principles, Pikachu might refuse to cooperate and try to show Ash that he's on the wrong path.
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.
His confidence might increase a great deal. Since legendary Pokemon are often seen as very powerful, Ash in his new form would feel more capable. He might become more solitary too, as some legendary Pokemon are known to be lone creatures.
He might become more cautious. Usually, Ash is quite bold and rushes into things. But if he's in a Team Rocket - centered fanfiction, he'd likely be more careful as he's constantly surrounded by danger. For example, he'd think twice before challenging a new Pokemon or entering an unknown area.
Naruto's positive and determined personality would likely boost the team's morale. His never - give - up attitude would inspire Team 10 members to push themselves further. For example, Choji might become more confident in his abilities and not be as hesitant during battles. Naruto's loud and boisterous nature could also liven up the usually more laid - back Team 10. Shikamaru, who is often thinking and strategizing in a quiet way, might be forced to be more vocal and assertive to keep up with Naruto.
Pikachu would probably be very confused at first. It's used to fighting against Team Rocket, not being on their side. It might resist and try to zap Ash to snap him out of it.
One reason could be its loyalty to Team Rocket. In many Pokemon stories, Team Rocket is the bad guy group. So, if Meowth is part of Team Rocket in the fanfic, when they do something really bad like trying to steal a rare and beloved Pokemon from a village, the villagers might catch Meowth and punish it instead of the whole team. They could make it do hard labor, like carrying heavy sacks of Pokemon food around the village all day long. This is because Meowth is more accessible and less intimidating compared to the other members of Team Rocket.