The plot could involve Ash being tricked by an evil entity into believing that the only way to achieve true power is to become an evil king. As an evil king, he might start changing the rules of Pokémon battles to suit his own desires. He could also start stealing rare Pokémon from trainers. His old friends would be shocked and would try to find out what caused this change in him. They would then embark on a journey to find a way to reverse the process and save Ash from his evil ways. Along the way, they might encounter new allies and enemies, all while trying to figure out how to deal with Ash's new - found power and malevolence.
Well, it really depends on how active the Pokémon fanfiction writers are in exploring this particular concept. I've seen fanfictions where characters are given completely different personalities. For Ash to be an evil king, it would change a lot of the dynamics in the Pokémon world. Writers could explore how his friends would react, how his Pokémon would behave, and what kind of chaos he would bring. You can also try looking on Wattpad in addition to the other sites mentioned earlier.
Another common theme is redemption. Even though he's evil, some fanfictions might explore the possibility of him changing or finding some sort of redemption for his actions. It adds an interesting layer to the character.
I'm not sure which specific 'ash the evil king fanfiction' is the best, but often checking out fanfiction communities on platforms like Reddit can be helpful. People there might be able to direct you to some great ones. They could also give you warnings about any that might not be so good in terms of plot or writing quality.
Gary could be the main antagonist. He has always been Ash's rival and seeing Ash turn evil, he might feel responsible to stop him. Gary could gather his own team of powerful Pokémon and use his wits to oppose Ash at every turn.
I'm not entirely sure specifically about this 'evil ash betrayed fanfiction' as there could be many different interpretations. It might involve the character Evil Ash in a situation where he betrays someone or something within the context of the fan - created story.
One interesting 'evil ash fanfiction' could be about Ash using his Pokémon in unexpected and devious ways to gain power in the Pokémon world. Maybe he teams up with some of the villainous teams in a plot that no one saw coming.
Obviously, Ash is a central character. Pikachu is also often there, as it's Ash's main Pokemon. Misty and Brock might be in the fanfiction too, trying to figure out what has happened to Ash and how to stop his evil ways. Sometimes, Gary Oak could be involved, either as an antagonist to Ash's new evil self or as someone trying to help bring him back to the good side.
Based on the title, Evil Ash is surely one of the main characters. But without reading it, it's hard to say who else might be involved. It could be characters from the original source material that Evil Ash has a relationship with, like his friends or enemies.
The novels similar to the two-faced Queen and the Monster King were recommended as follows:
1 "Thousand Bones of Flowers"-Zhao Liying
2. Biography of Chu Qiao-Zhao Liying
3."The Poisonous Daughter of a Concubine"-Yang Mi
4 "Palace Heart Locking Jade"-Yang Mi
5."Startling Step by Step"-Startling
6 "Fuyao"-Yang Mi
7 "Concubine's Daughter"-Electric Wires
8 " Secret Service Concubine: Chu Qiao's Biography "-Zhao Liying
9 "Thousand Flowers"-Zhao Liying
10 "Beautiful Unending"-Tang Yan
These novels are all very famous for their twists and turns. I hope you will like them!