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.
Definitely. One idea could be that a fellow Pokemon trainer whom Ash has helped in the past betrays him by trying to take credit for Ash's achievements in training his Pokemon. This trainer could go around saying that they were the ones who taught Ash certain training techniques when in fact it was all Ash's own hard work. It's a form of betrayal that focuses on Ash's reputation and success rather than anything sexual.
The emotional turmoil is a big consequence. The girls in the harem might experience heartbreak, anger, and confusion. This can change their personalities and the dynamics of the harem. For example, a once - happy - go - lucky girl might become withdrawn. And if the fanfic has a larger plot outside of just the harem, Ash's betrayal could also affect his ability to achieve other goals, like winning battles or achieving some sort of quest. Because the harem might have been a source of support, both emotionally and in terms of resources, and now that's all disrupted.
In fanfiction, a story of Ash, Haruka (May in the English version), and Dawn could involve betrayal and hurt in many ways. For example, perhaps Ash makes a promise to both Haruka and Dawn about their Pokémon journey together, like he'll always be there to support them in battles and training. But then, he might break that promise by suddenly leaving them for a more 'glamorous' opportunity in another region without any prior notice. This would make them feel betrayed and hurt, as they relied on him not just as a friend but also as a partner in their Pokémon adventures.
Power struggle can also be a theme. If Diantha betrays Ash for power, it shows how power can corrupt and change a person's values. It could also lead to a battle of wills between them, as Ash might try to oppose Diantha's new -found power - hungry ways. This theme often explores the darker side of human (or in this case, trainer) nature when faced with the allure of power.
One reason could be power. Maybe he was offered a great deal of power by an outside force in exchange for betraying the harem. Another could be jealousy. If there was someone in the harem who was getting more attention or was more successful than him in some way, he might have been driven by envy to betray them.
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.
In such a fanfiction, perhaps Ash betrays his friends for power. He might be lured by an evil organization with the promise of rare Pokémon or ultimate power, and in the process, turns his back on Pikachu and the others.
In some fanfictions, Ash might become evil after betrayal when his trust is shattered. For example, if his friends turn on him for some false accusations, he could start to see the world in a different, more cynical way. This broken trust might lead him to believe that power is the only thing that matters, and he starts to pursue it without regard for the consequences, gradually turning evil.