In certain fanfictions, a Pokémon professor or an authority figure in the Pokémon world could betray Ash. They may have their own secret agendas. For example, a professor might use Ash's research data without his permission or manipulate him into dangerous situations for their own experiments. This would make Ash feel extremely betrayed as he looks up to these figures for guidance.
Team Rocket is a likely candidate. They're always up to no good and hypnotizing Ash would be just another devious plan for them. They could use it to finally capture Pikachu. Giovanni, as their leader, might also be involved in such a scheme. Another character could be a powerful and envious trainer who wants to eliminate Ash as competition by hypnotizing him and making him lose his skills.
Some fanfictions might have Misty betray Ash. Perhaps she gets lured by the promise of power or some valuable reward. She could be tricked into believing that Ash is no longer the friend she thought he was and that betraying him is for the greater good.
In fanfiction, Gary could be a likely character to betray Ash. He has always been a rival and might have ulterior motives. For Dawn, Zoey could potentially betray her. Zoey has been a tough competitor and might be jealous enough to take some underhanded actions. Another possible betrayer for Ash could be Team Rocket. They've been after his Pikachu for a long time and could use betrayal as a new tactic. For Dawn, perhaps a new coordinator who is envious of her popularity in the coordinator world.
Gary Oak is a likely character. He has always been a rival to Ash and in fanfiction, he might betray Ash out of jealousy or a desire to be the ultimate Pokémon trainer. Another could be Misty. Maybe she gets influenced by some external force or her own insecurities and turns against Ash. Brock could also be a candidate in some stories. If he falls in love with a girl who has a vendetta against Ash, he might be forced to choose between his loyalty to Ash and his new love interest.
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.
His rivals could be the ones to betray him. For example, Gary Oak might see Ash's godlike powers as a threat to his own status and decide to plot against him. Gary could spread false rumors about Ash to turn others against him.
Gary could be a likely character. He has always been Ash's rival and there could be a plot where his jealousy or some other motive leads him to betray Ash. Another could be one of his so - called friends from the Pokemon League who might be influenced by power or some dark secret. Or, in some really dark fanfictions, it could be a Pokemon that Ash trusted deeply but for some reason turns on him.
One likely character could be a rival trainer. They might see Fem Ash as a threat and betray her to get an edge in competitions. Another could be a so - called friend who is jealous of Fem Ash's success.
Gary Oak could be a likely betrayer. He has always been Ash's rival, and in some fanfiction, he might take things too far and betray Ash in a crucial Pokémon battle, like using underhanded tactics to win. This would surely make Ash cry.
Their closest friends like Brock and Misty would surely be affected. They've been through so much with Ash, and his betrayal would be a huge shock. And for Lyra, her friends in her own region might be deeply hurt.