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.
One possible reason could be jealousy. Maybe Ash has achieved more in his Pokemon journey than his friends, and they can't handle it. Another reason might be some misunderstanding. For example, an enemy could trick Ash's friends into thinking Ash has done something bad. Or perhaps there's some sort of power struggle. If there's a powerful item or a rare Pokemon involved, and Ash is the main contender, his friends might be tempted to betray him for their own gain.
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.
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.
In most Pokemon fanfictions, this is not the case. Ash is typically portrayed as a character who values his friends deeply. Fanfictions usually build on the strong bonds he has with his friends in the original series. However, there might be some very rare and out - of - the - ordinary fanfictions that take a different approach, but it goes against the general essence of the Pokemon story.
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.
Jealousy could be one reason. Maybe his friends are jealous of his achievements as a Pokémon trainer. Another reason could be that they are influenced by some external forces, like an evil organization that convinces them to betray Ash.
Ash could respond in different ways. He might try to confront his friends immediately to get an explanation. If the betrayal is really bad, he could cut them off completely and focus on his own goals, like becoming a better Pokémon trainer. He would also probably have some internal struggles, as he has memories and experiences with these friends that he can't just forget.
Ash would probably be initially shocked. He has always trusted his friends, so the idea of betrayal would be hard to swallow. He might try to talk to them, to find out why they are doing this.