Well, a plot twist could be that the whole Orre region was a set - up by a powerful enemy to trap Ash. So all the people and Pokemon he meets there are in on the scheme. Or perhaps Ash discovers that his own actions in the past unknowingly led to a situation where he is now betrayed in Orre. It could also be that the betrayal is just an illusion created by a psychic - type Pokemon to test Ash's resolve.
One possible plot twist could be that the person Ash thought was his friend in Orre turns out to be working for an evil organization. Another could be that Ash's Pokemon are somehow brainwashed against him. Maybe the betrayal leads to Ash losing his ability to communicate with his Pokemon for a while.
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.
One interesting idea for the fanfiction is that May betrays Ash to protect her family. An evil group threatens her family and the only way to save them is to turn against Ash. This would create a complex situation where May is torn between her loyalty to Ash and her love for her family. Ash, on the other hand, would be completely blindsided by her sudden change in behavior.
It could be that Mew has some sort of special power or knowledge that certain groups in the Pokémon world are after. They see Ash as an obstacle to getting what they want from Mew. So, they scheme to make everyone think Ash is untrustworthy. His friends, not knowing the truth, end up betraying him. Ash then has to fight against all odds to protect Mew and regain the trust of his friends.
One possible plot could be that within the fanfiction world, there is a new character introduced who seems to be a great ally at first. This character gains the trust of Ash and Brock over time. However, this new character has a hidden agenda. They might be from a rival region and their goal is to undermine Ash and Brock's reputation in the Pokemon world. So they start spreading false rumors about them and turn other trainers against them, thus betraying their new - found friendship.
Well, perhaps Clemont betrays Ash because he becomes envious of Ash's success. Maybe he gets influenced by some dark force in the Pokemon world that convinces him to steal Ash's Pokemon or to lead him into a dangerous trap.
One possible plot twist could be that Paul has an ulterior motive for saving Ash. Maybe he wants to use Ash for his own gain later on.
In such a fanfiction, the plot could involve Ash being betrayed by his long - time friends. Maybe they envy his success in the Pokemon world. For example, Gary could spread false rumors about Ash in the new region, causing the local trainers to distrust Ash. This would make Ash's journey in the new region much more difficult as he has to not only deal with new Pokemon and challenges but also regain his reputation.
It could be that Lillie betrays Ash because she believes it's the only way to achieve a greater good in the Pokémon world. She might think that Ash's methods are too dangerous or not in line with what she believes is right for the future of Pokémon and humans alike. This would create a complex conflict between their ideologies.
One possible plotline could be that her so - called friends in the Pokemon journey turn against her for some reason, like jealousy over her Pokemon's strength. Maybe they try to steal her Pokemon or spread false rumors about her to isolate her.
Perhaps a new and powerful trainer arrives in the story. This trainer manages to deceive Ash's harem members, making them think that Ash is a hindrance to their growth as trainers. As a result, they side with the new trainer and betray Ash, leaving him feeling confused and alone.