Well, it might be that his rivals in the fanfiction somehow manage to deceive his Pokemon into thinking Ash is a bad trainer. Maybe they spread false rumors about how he doesn't really care for them, which causes the Pokemon to betray him. This would shatter Ash's world as his Pokemon are his closest friends and partners.
Ash would probably be devastated. He would feel like his world has been turned upside down. At first, he might not believe it and think it's all a big mistake. As the reality sinks in, he could start to isolate himself from others, even from his Pokemon for a while. However, his strong will would eventually kick in. He would use this as motivation to become stronger, not just in his Pokemon battles but also in his ability to face challenges alone, without relying on his so - called friends.
There's also a chance that an old enemy from Ash's past resurfaces. This enemy, who has a long - standing grudge against Ash, could find a way to use Ash's Pokemon to get revenge. They might have developed new techniques or powers over time that allow them to influence the Pokemon's loyalty.
One possible analysis could be that in such a fanfiction, the idea of Ash being betrayed might be a way to create drama. It could involve his friends or companions in the harem turning against him for various reasons like jealousy or misinformation.
Some of his more loyal Pokemon might try to resist the change. For example, Pikachu could use electric shocks to try and jolt Ash back to his senses. Pikachu has a strong bond with Ash and would be very confused and sad about his decision to join Team Rocket.
It's hard to say it's extremely popular across the whole Pokemon fanfiction community. There are many different themes in Pokemon fanfiction. While the idea of Ash being betrayed in the Orre region could attract some readers who are interested in exploring darker or more complex storylines within the Pokemon world. But compared to more common themes like Ash's journey to become a Pokemon master with his regular team, it might not be as widespread.
In such a fanfiction, Ash might become extremely isolated. He could lose faith in his Pokémon and himself. Maybe he'd leave the Pokémon world in despair, feeling that all his efforts were in vain. Without the support of his friends and Pokémon, his once - strong will to be a Pokémon Master could crumble completely.
Well, in many such fanfictions, it could involve Ash being betrayed by Clair perhaps in a Pokémon battle strategy. Maybe Clair teams up with an unexpected rival against Ash, or she might break a promise regarding Pokémon training or a joint adventure.
In such a fanfiction, perhaps Ash could be betrayed by his friends in Alola. Maybe they misunderstand his actions or are influenced by some false information. For example, they might think Ash is secretly working for an enemy, which leads to the betrayal.