Maybe there's a rogue Pokemon trainer. This trainer is jealous of Dawn's skills and the attention she gets. When Dawn joins Team Rocket, this trainer sees it as a chance to expose her as a fraud. He or she then tries to stop Dawn and Team Rocket's activities, thinking that they are up to no good, which they are, but the trainer has his own self - centered motives.
Giovanni is usually a main character. He's the leader of Team Rocket and in the Rainbow Rocket scenario, he's a central figure. Lysandre from Team Flare could also be a main character. His extreme views and his connection to the Rainbow Rocket's overall plan make him important. And of course, the protagonist of the fanfic, who could be a young trainer trying to stop their evil plans.
One idea could be exploring the backstories of the Rainbow Rocket members in more detail. For example, Giovanni's motives and how he assembled the team. Another could be a scenario where the protagonist has to infiltrate the Rainbow Rocket base. Maybe they have to find a way to stop a new, more powerful weapon the team is developing.
Lyra might also be used as a tool to explore the backstories of Team Rocket members. By interacting with them, she could uncover secrets and past traumas that led them to join Team Rocket in the first place. This can add depth to the fan fiction and make the characters more relatable.
Well, in many Team Rocket fan fictions, Lyra can be depicted in various ways. She could be a new recruit who is initially naive about Team Rocket's true intentions. Maybe she joins thinking it's all about adventure and then discovers the darker side.
Another plotline might involve Ash teaming up with some of the Team Rocket members, perhaps reluctantly at first. They could be forced to work together due to a common threat to both the good guys and the bad guys in the Pokemon universe. This would lead to some interesting character developments for Ash as he has to deal with the not - so - good nature of 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.