He could be very depressed at first. Losing such an important title that he may have worked hard for or believed in for a long time can be a huge blow to his self - esteem.
One reason could be that he fails a major quest. For example, if there's a prophecy that he must defeat a certain powerful villain to maintain his 'Chosen One' status and he doesn't succeed. Maybe the villain was too strong or Ash made a crucial mistake during the battle.
Ash would probably be very confused at first. He might try to reason with Latias, asking her why she is doing this. If she doesn't respond, he would start looking for ways to escape. He would also be worried about his Pokémon and his friends, wondering if they are safe.
In these fanfictions, Ash often becomes more confident. Since he is the chosen one, he has a greater sense of purpose. For example, he may be more decisive in battles, quickly choosing the right Pokemon to send out.
In these fanfictions, Ash is usually depicted as having a special connection with pokemon that goes beyond what is shown in the regular series. He can sense their emotions more acutely and communicate with them in ways that others can't. This is part of what makes him the chosen one. For example, he might be able to calm a wild and enraged legendary pokemon just by approaching it, showing his unique bond with all pokemon. He also tends to be more strategic in battles, using his new - found status and abilities to outwit his opponents.
Ash as the Chosen One in Pokemon fanfiction is a really interesting concept. It gives a whole new layer to his character. He could be given a special Pokemon by some mysterious force that is crucial for his destiny. This Pokemon might be one that no one has ever seen before. His friends would also play different roles, perhaps as protectors or guides to help him fulfill his chosen - one duties. And his battles would become even more epic as he has this greater responsibility on his shoulders.
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.
Ash would probably be initially shocked. He is used to seeing the good in people and would not expect such a betrayal from Cynthia. He might stand there in disbelief for a moment, unable to process what has just happened.
First, you need to define what it means for Ash to be the chosen one in your story. Is it a prophecy? A special power? Then, plan out his journey. Decide on the challenges he'll face, like powerful villains or difficult Pokémon to catch. You can also add new characters that are related to his chosen - one status. For example, a mentor who knows about the prophecy.
Ash would be extremely devastated. Pikachu is not just his Pokémon but also his closest friend. He would likely first try to reason with Pikachu, not believing that Pikachu could truly betray him. He might be in denial for a while.
Some of the more intelligent Pokemon on his team, like Bulbasaur or Squirtle, might try to find a way to reverse the transformation. They could search for special herbs or items in the Pokemon world that they think could help Ash return to his normal state. And during this process, they would have to protect Ash from any potential dangers that his new form might attract.