At first, his friends might not believe it's Ash. But when he starts to show his usual personality traits, like his determination and kindness, they would start to accept it. They would then start to think about how they can use Ash's new form to their advantage. For example, they could use his ability to fly as Mew to reach places they couldn't before, or his psychic powers to sense danger from afar.
He would probably be very confused at first. He'd look around, trying to figure out where he is and how he got there.
Well, one possibility is that Ash wakes up with all the powers of Mew. He could then use these powers to quickly become the best Pokémon trainer ever. He might be able to communicate telepathically with all Pokémon, understand their needs and desires instantly, and use his newfound psychic abilities to battle more effectively. For example, he could levitate his Pokémon during battles, giving them an unexpected advantage.
His friends would be extremely shocked at first. Misty might scream and be really confused about what's happening to Ash. Brock, on the other hand, would probably try to stay calm and start thinking of ways to reverse the transformation right away. They would all be worried about how Ash is feeling in his new form and if he's in any pain. They would also be concerned about how they can still communicate with him effectively, since he's becoming a Pokemon.
At first, his friends would be in disbelief. But then, they would start to adapt. Dawn might see it as an opportunity to study a Pokémon from a different perspective. Gary could be both amused and intrigued, and might offer some scientific theories on how it happened. Overall, they would all be concerned for Ash's well - being and work together to either help him get back to normal or help him thrive in his new form.
His friends would be very shocked at first. Misty might be a bit worried and try to find a way to turn him back quickly. Brock, on the other hand, would be more curious and start observing Ash - as - Pikachu to see how his behavior has changed. His Pokémon friends would also be confused. Pikachu himself might be both excited to have a 'Pikachu - like' friend but also a bit sad that his trainer is in this strange state.
Ash would probably be initially shocked. He has always trusted his friends, so the idea of betrayal would be hard to swallow. He might try to talk to them, to find out why they are doing this.
His friends might be really confused at first. Pikachu, for example, might give Ash some really puzzled looks. If Ash tries to explain to his friends that they're all part of a fanfiction, some of them might not believe him at all. Misty could think Ash has hit his head or something and is just spouting nonsense.
His best friend Pikachu might be a bit confused at first but would quickly adapt as it still senses Ash's essence. Brock would probably be very surprised and might offer some comical comments or advice on how to handle the new situation. Misty could be a mix of shocked and intrigued. She might be a bit jealous of Ash's new female appearance at first, but then would support him as they are friends.
His character could develop a more gentle side. Mew is often associated with kindness and playfulness. As Ash becomes a Mew fan, he might start to exhibit these traits more. For example, he could be more patient with his other Pokémon and more understanding of their needs, rather than just focusing on winning battles.
Their friends like Brock would probably be very excited. Brock, being knowledgeable about Pokémon and also having a nurturing side, would offer all kinds of advice on taking care of May during the pregnancy. He might even cook special meals for her to ensure she has all the nutrients she needs.