Ash could get angry. He has a strong sense of justice, and he might feel that May has violated their friendship. He could challenge her, not in a violent way, but more in a way to get an explanation and to try to make her see the error of her ways. He would likely be determined to show her that what she did was wrong.
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.
Ash would likely be shocked at first. He's so used to seeing the good in people, especially fellow trainers. But then he'd probably get angry and determined to set things right. He has a strong sense of justice, so he wouldn't let the betrayal go unpunished.
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.
I think Ash would be angry as well as hurt. He's a passionate trainer and his friends mean a great deal to him. He might challenge May in a Pokémon battle, not to defeat her but to make her see how wrong her betrayal is. And during the battle, he would keep asking her to come back to their old friendship.
Ash would be extremely hurt. He's a very loyal person, and having someone he cares about like Lillie betray him would be a huge blow. He might initially go into denial, not believing that Lillie could do such a thing.
Ash would feel a deep sense of betrayal that could shatter his usually upbeat attitude. He might go through a period of self - doubt. However, his love for his Pokémon and his sense of justice would pull him out of it. Mewtwo, having already experienced betrayal from humans in the past, would be filled with a cold fury. It would use its psychic abilities to gather information about the betrayers. Ash and Mewtwo would work together, Ash learning from Mewtwo's insights and Mewtwo being inspired by Ash's tenacity in the face of betrayal.
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 be heartbroken. He has a deep bond with Charizard, and seeing it turn against him would be like losing a part of himself. He would probably first try to reason with Charizard, thinking that there must be some mistake. When that doesn't work, he might become a bit angry, but mostly he'd be sad and determined to find out what's wrong and fix it.