Well, if Misty joins Team Rocket in fanfiction, it would be a huge shock to the other characters. Her friends like Ash would be completely bewildered. Maybe she's been tricked into it somehow, like being deceived by Team Rocket's false promises. This could lead to some really interesting plot twists. For example, she might be used to set traps for Ash and the others, but deep down still have some good in her that causes internal conflict within Team Rocket.
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.
The plot might involve a power struggle within Team Rocket. Ash and Misty could be brought in because they possess certain skills or knowledge. For example, Ash's bond with his Pokémon could be seen as a valuable asset. Misty's understanding of water - type Pokémon might also be desired. However, they soon realize that they are being used in a power play between different factions of Team Rocket, and they must decide which side to take or find a way to break free from the whole mess.
Ash's character might become more conflicted. He has always been the hero, fighting against Team Rocket. But now, being part of them, he would question his own values. He might initially try to change Team Rocket from the inside, but as he faces more and more of their evil deeds, he would struggle between his loyalty to his new 'team' (out of a sense of obligation since he joined) and his true nature of being a Pokémon protector. Misty, on the other hand, would probably be more outspoken about her dislike for Team Rocket's actions and try to convince Ash to leave sooner.
Misty's Pokemon could be involved in a way where they are all captured by Team Rocket. Then Misty has to rely on her wits and some basic Pokemon - handling skills without her actual Pokemon. She has to find a way to free them. Meanwhile, her Pokemon are trying to communicate with other wild Pokemon in Team Rocket's base to create a sort of uprising. This would lead to a big showdown where Misty and her freed Pokemon take on Team Rocket and their own captured Pokemon.
One potential consequence is that it would damage her relationships with her former friends. Ash and Brock would be very disappointed in her. Also, the Pokémon she had would be in a difficult situation. They might not be used to the unethical ways of Team Rocket. Another consequence could be that the balance of power in the Pokémon world would shift slightly. Team Rocket would gain a more competent member, which could make them more of a threat to other trainers and Pokémon centers.
Well, in the 'Ash and Misty joins Team Rocket fanfic', they could be brainwashed by Team Rocket's technology or some devious plan. Once they join, they might be given new uniforms and tasks. They could be involved in stealing Pikachu again, but this time from the other side. It would create a whole new dynamic in the Pokémon world, with their old allies now becoming their enemies.
Well, it could make for a really interesting fanfiction. Dawn joining Team Rocket would change the whole dynamic. Her Pokémon might not be too happy about it at first. She could bring new ideas to Team Rocket, since she has a different way of thinking compared to Jessie, James and Meowth. However, it's also possible that she would secretly be working against Team Rocket from the inside, trying to take them down while pretending to be one of them.
One possible storyline is that Dawn joins Team Rocket thinking it's a legitimate Pokémon training organization at first. But as she gets deeper into it, she discovers their true evil nature. Another could be that she is brainwashed by Team Rocket into joining them. Her friends then have to find a way to break the brainwashing. A third storyline could be that she joins willingly because she has some sort of vendetta against the Pokémon League and sees Team Rocket as a way to get revenge.
One possible plot could be that Misty gets captured by Team Rocket. They plan to use her as a bargaining chip against Ash. But during her captivity, she manages to befriend some of the lower - level Team Rocket grunts. These grunts start to have second thoughts about their evil deeds because of Misty's influence. Eventually, Misty uses this new - found friendship to escape and also cause some internal chaos within Team Rocket.