Perhaps Ashley betrays Ash by revealing his battle strategies to other trainers. In the Pokemon world, strategies are crucial, and this could lead to Ash losing battles. As a result, Ash might feel extremely disappointed and have to come up with new strategies while also dealing with the betrayal.
It could be that Ashley was working undercover for an evil organization all along. She pretends to be Ash's friend but then at a critical moment, she hands over important information about Ash and his Pokemon to the organization. This would put Ash and his Pokemon in great danger, and he would have to fight not only to protect himself but also to expose Ashley's true motives.
Perhaps Leaf betrays Ash because she becomes jealous of his friendship with Pikachu. She might feel like Pikachu gets all of Ash's attention and decides to side with a group that wants to separate them. This could lead to Ash having to fight not only to save Pikachu but also to win Leaf back.
Maybe there is an evil Pokemon trainer who has influenced Ashley to betray Ash. In this case, that trainer would be the main antagonist. He or she might have promised Ashley something in return for her betrayal, like rare Pokemon or power.
In 'Goku betrayed fanfiction', a common plot might be the corruption of his power. Let's say Goku discovers a new form of power that is seen as too dangerous by others. His friends and even some of the Z - fighters fear that he'll lose control and turn on them. So they decide to betray him first to protect the Earth. Another aspect could be a political betrayal. If there were some sort of intergalactic politics involved, Goku might be sacrificed or betrayed by his own side to make a deal with a more powerful alien race. And then there's the idea of a time - travel - related betrayal. Maybe someone from the future comes back and convinces everyone that Goku will cause a great disaster in the future, causing them to betray him in the present.
One possible storyline could be that Percy is tricked into betraying Tartarus by some dark force. Maybe they use his friends as hostages or manipulate his mind. Another could be that Percy believes he's doing the right thing in betraying Tartarus, but later realizes it was a huge mistake and has to face the consequences. For example, he might face the wrath of Tartarus' minions or lose the trust of his allies.
One possible storyline could be Dawn's struggle to balance her Pokemon training journey with her pregnancy. She might have to deal with the physical limitations and the reactions of her friends and family. Another could be about the mystery of how she became pregnant in the Pokemon world, perhaps involving some rare Pokemon power or event.
One possible storyline could be that Natsu is wrongly accused of a crime within the Fairy Tail guild. Maybe some false evidence is planted against him, leading the guild members to turn their backs on him. Another could be that a powerful enemy manipulates the guild into believing Natsu is a threat, so they betray him. It might also be that there's a misunderstanding about Natsu's powers or intentions, causing the betrayal.
Ashley Clemont could also be a character in a more romantic - themed Pokemon fanfiction. Maybe she has a crush on Clemont, and the story revolves around their relationship as it develops while they travel through the Pokemon world. This could involve them sharing special moments with their Pokemon, and using those experiences to grow closer to each other.
One possible scenario could be that Ash betrays May for a powerful Pokemon. Maybe he gets offered a super rare and strong Pokemon but has to cut ties with May to get it. Another could be that May betrays Ash because she is influenced by a rival trainer who convinces her that Ash is holding her back from reaching her true potential as a Pokemon trainer.
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.
In addition to Ash's friends, there could be some villains in the fanfiction. They might be the ones who initiate the betrayal. For example, some Team Skull members could play a role. They might manipulate the situation to make Ash's friends believe that he is not trustworthy. Also, some mysterious new trainers in Alola could be involved, either as instigators or as characters who try to help Ash later.