Perhaps in this fanfiction, the Pokémon League in Kalos has some sort of dark secret. When Ash becomes champion, he discovers this secret. His friends, who are actually in league with the corrupt elements of the league, betray him to keep the secret safe. Ash then has to fight not only against his former friends but also against the entire corrupt system of the Kalos Pokémon League.
One possible plot could be that Ash's so - called friends in the Kalos region turn on him out of jealousy. Maybe they can't handle the fact that he has become the champion. They start spreading false rumors about him, which makes the public turn against Ash. This betrayal could lead Ash to question his own journey and the relationships he has formed.
One likely betrayer could be Serena. Maybe she has some hidden motives that are revealed when Ash becomes champion. For example, she might be jealous of his success and the attention he gets as champion, and so she betrays him.
A great 'Ash becomes Kalos Champion' fanfiction would have a strong sense of progression. Ash should start at a certain level and gradually become more powerful as he overcomes various obstacles in Kalos. The fanfiction could also explore the backstories of his Pokémon in more detail, like how they came to be with Ash and what their own goals are. Additionally, the way Ash interacts with the local Pokémon and trainers in Kalos can add depth and authenticity to the story.
In an Ash betrayed champion fanfiction, perhaps the champion has been secretly working with a villainous group. The champion lures Ash into a trap under the pretense of a friendly battle. Ash, being trusting, falls for it. He then has to find a way to escape and get revenge. He might meet some new allies along the way who help him see the champion's real motives.
The plot could involve Ash facing his toughest rivals from all the regions he has visited. He might have to overcome personal doubts and insecurities along the way. His Pokémon team could gain new powers or evolve at crucial moments. For example, his Charizard could return and play a key role in a battle. The final battle could be against a mysterious and powerful trainer who has a unique set of Pokémon. Ash would need to use all his experience and knowledge to win.
One possible plot could be that Ash returns as a champion but is betrayed by his former friends who are jealous of his new status. They might spread false rumors about him, causing him to lose the support of the people. Ash then has to prove his worth all over again and show that he is still the same person at heart.
One possible plot could be that Ash is betrayed by his friends in the Alola region who are jealous of his champion status. They might spread false rumors about him, which leads to his isolation. For example, they could claim that he used unfair means to win the championship. This would make Ash feel betrayed as he thought they were his true friends.
One idea could be Ash facing a new, extremely powerful and mysterious Pokémon in the Kalos region that no one has ever seen before. This Pokémon could be the key to a hidden power within the Kalos champion title. Another plot could involve Ash having to team up with a former rival from his past travels to overcome a threat to the Kalos Pokémon ecosystem. Maybe there's a dark organization trying to disrupt the balance, and Ash's unique bond with his Pokémon is what's needed to stop them.
A great plot twist could be that the Kalos champion turns out to be an impostor. Ash discovers this during his journey towards the championship. This would mean that all the battles leading up to the championship were based on a false premise. Ash then has to not only expose the impostor but also face the real champion in a series of unforeseen challenges. Also, there could be a twist where Ash's Pikachu loses its ability to use electricity temporarily, forcing Ash to rely on his other Pokémon in new and creative ways.
It could be a local Kalos trainer who has been training specifically to become the Kalos champion for years. This trainer might have a team of rare and powerful Kalos Pokémon and a very strategic battle style. He or she could see Ash as an outsider and a threat to their long - held dream of being the champion.
Maybe Team Rocket. They've been after Ash for a long time. If Ash comes back as a champion, they might see it as a threat and betray him in some way. They could pretend to be his friends at first and then stab him in the back to get what they want, like his powerful Pokémon or his championship title.