The plot could revolve around Ash's initial confusion and conflict. He might join Team Rocket thinking he can change them, but soon realizes it's not that easy. His loyalty to his old friends would be tested as he gets drawn deeper into Team Rocket's plans.
Well, if Ash joined Team Rocket, he'd probably bring a whole new dynamic. His skills as a trainer could be used in unexpected ways. Maybe he'd try to reform Team Rocket from the inside, using his kind heart and love for Pokémon to change their ways. He could also introduce new strategies for capturing Pokémon that are more ethical than Team Rocket's usual methods.
If Ash joined Team Rocket in a fan fiction, his Pokémon might be really confused at first. Pikachu, for example, is used to Ash being a good guy. But over time, they could adapt. Ash could start to see the Pokémon world from a different perspective, like how Team Rocket views Pokémon as a means to gain power and wealth. However, deep down, Ash's kind heart might still shine through and he could end up changing Team Rocket from the inside instead of fully becoming a bad guy.
Maybe a new, mysterious villain who has a grudge against Ash or wants to use his skills for their own evil purposes. This villain might be from a far - off region and has special powers that allow them to hypnotize people. They see Ash as a useful tool to carry out their plans in the Pokémon world.
His rival, Gary, could be a likely candidate. Gary has always been competitive with Ash, and in this fanfiction, his jealousy could reach a boiling point, causing him to betray Ash for his own gain, like trying to steal his Pokémon or get credit for his achievements.
Ash could become more confident and wise as a Dragon Master. His decision - making skills would improve as he deals with powerful and often unpredictable dragon Pokémon.
The Pokémon might initially think it's some sort of joke or mistake. But as time goes on, if Ash seems serious about being with Team Rocket, they could become divided. Some of the more headstrong Pokémon might leave Ash, while others might stay with him out of loyalty but still be unhappy about the situation. They would be constantly trying to nudge Ash back to his old ways of being a good Pokémon trainer.
One good fanfic could be 'Ash's Homecoming'. It focuses on Ash returning home to Pallet Town and his heartwarming interactions with Delia. It shows their strong bond through simple daily activities like having dinner together and sharing stories of his adventures.