It could be a rival trainer. Rival trainers are often very competitive in the Pokémon world. Maybe this rival is jealous of Ash and May's progress and decides to betray them to slow them down. They might spread false rumors about Ash and May, causing other trainers to be distrustful of them.
They could start traveling together more often. As they journey side by side, they'll face different challenges. For example, they might encounter a Pokémon that is difficult to catch or train. Working together to overcome these obstacles will deepen their bond. Also, they could participate in combined Pokémon events, like a battle - contest hybrid event. There, they'll have to rely on each other's strengths, which will bring them closer.
One possible storyline could be that May and Ash team up to face a powerful new threat in the Pokémon world. They train together, with May's Contest skills and Ash's battle expertise complementing each other. Another could be that May helps Ash in his journey to become a Pokémon Master, providing support and advice based on her own experiences. Maybe they even discover a new region together and explore it, encountering new Pokémon and making new friends along the way.
Yes, it probably exists. In many fandoms, there are fans who create fanfiction about various character pairings. Pokémon has a large fan base, and Ash and May are well - known characters, so it's very likely that some fans have written fanfiction about them.
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.
It could mean that in a fan - created story (fanfiction), a character named Ash is saving a character named May. Maybe Ash is rescuing May from a dangerous situation like a battle with a powerful Pokémon or from some other kind of trouble in the fictional world of Pokémon fanfiction.
In certain fanfic ideas, Arceus could be influenced by an evil force. This evil force manipulates Arceus into believing that Ash will cause great harm in the future. So, Arceus betrays Ash as a preventive measure, according to the fanfiction plot. However, this is just a fictional concept and not part of the official Pokémon storyline.
It could be Gary. Gary has always been a rival to Ash. Maybe in this fanfiction, Gary gets jealous of Ash's progress and decides to betray him by making false accusations to the Pokemon League about Ash using illegal training methods.
Maybe Team Rocket. They've been after Ash for a long time. If Ash comes back as a champion, they might see it as a threat and betray him in some way. They could pretend to be his friends at first and then stab him in the back to get what they want, like his powerful Pokémon or his championship title.
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.