One possible plot could be that his mom reveals she has been working with an evil organization all along. She hands Ash over to them for some dark purpose, like using his unique Pokémon connection for their evil experiments. Ash would feel extremely hurt and betrayed, having to then find a way to escape and also come to terms with his mother's true nature.
If his mom betrays Ash, it's possible that there are other family members or old friends who support his mom's actions. They could become antagonists as well. Maybe an uncle who has always been jealous of Ash's potential and sees this as an opportunity to get rid of him. Or a family friend who has some hidden motives and helps his mom in the betrayal. These characters would then be obstacles for Ash as he tries to overcome the betrayal and move forward.
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.
Well, if Ash and his brother 'betrayed' fanfiction, it might be that they promised to contribute to the fanfiction world in a certain way but didn't follow through. For example, they could have agreed to help promote or write for a particular fanfiction project and then backed out. Another possibility is that they used fanfiction in a way that was considered unethical, like taking credit for someone else's work that was part of the fanfiction realm.
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.
Well, often in such a 'ash gets betrayed fanfiction', the story might start with a seemingly normal day for Ash. Then, out of the blue, someone he trusts deeply, like Pikachu or one of his human friends, does something that he perceives as a betrayal. This could be something as simple as not believing in him during a crucial battle or siding with an enemy for a reason that's not clear to Ash at first. It can create a lot of emotional turmoil for Ash and make for a very engaging read.
One possibility could be that in the fanfiction, Ash betrays Latias out of a misunderstanding. Maybe he was tricked by a villain into believing that Latias was a threat to the region. This would create a lot of drama and conflict in the story as Latias, who probably trusted Ash, would be deeply hurt.
In fanfiction, a story about Ash and Latias being betrayed could be really heart - wrenching. Maybe it could involve Ash being wrongly accused by his friends and Latias being forced to turn against him due to some dark magic or false information. It might explore themes of trust and friendship being broken.