Reacting with anger might not be the best option, but it's a valid one. You could show him that his actions have consequences. However, be careful not to push him further away. Maybe say something like 'I'm hurt by what you've done, but I still care about you. If you change your mind, I'll be here.' This shows your strength but also your willingness to forgive.
One way to react is to try and talk to him. Reach out and ask him why he's doing this. Maybe he'll be open to communication and you can clear up any misunderstandings. For example, you could say something like 'I don't understand why you've turned your back on me. Can we talk?'.
Jaune might react with shock at first. It's like his world is turned upside down suddenly.
He might have turned his back on you because of a misunderstanding. In RWBY's complex world of fanfiction, miscommunication is common. Maybe he thought you did something wrong when you actually didn't. For example, if there was a situation where it seemed like you betrayed a group, but in reality it was a setup, he could have turned his back in anger without knowing the truth.
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.
I think his friends' reactions would vary. Naruto's closest friends like Shikamaru and Kiba would quickly realize that they need to support Naruto. They would see that despite the strange new form, it's still Naruto. Sakura would be more emotional, she might cry at first but then pull herself together to help. And Sasuke, he would probably see it as an opportunity for Naruto to gain more power, but also be cautious in case the Titan form has any negative effects on Naruto's mind.
At first, his Pokémon would be startled. They've always known Ash as a human. But then, they would start to adapt. Some Pokémon, like Squirtle, might try to play with Ash in his new form, thinking it's a new kind of game. However, his more loyal Pokémon, like Greninja, would be determined to find a way to turn Ash back. Greninja might use its special bond with Ash to try and communicate with him on a deeper level in this new form, to understand what happened and how to reverse it.
His other Pokémon like Charizard would be completely bewildered. Charizard might initially think that this Eevee is just some random Pokémon near its territory. But when it senses something familiar about the Eevee, it would be hesitant and curious. It could try to communicate in its own way, like using small bursts of fire to get the Eevee's (Ash's) attention. The Pokémon that Ash has a closer bond with would be more determined to figure out what's going on and how to help him.
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.
At first, Naruto might be really confused. He's used to thinking of his friends as his support system, so when they turn on him, he doesn't understand why. He'll probably try to talk to them, to ask what he did wrong. If they don't listen, he could become really sad and withdrawn. Maybe he'll start training even harder, using the pain of being rejected by his friends as motivation to become stronger.
Anakin might be shocked at first. After all, he may not have expected to ever meet his father. He could be hesitant and full of questions.
Ash could respond in different ways. He might try to confront his friends immediately to get an explanation. If the betrayal is really bad, he could cut them off completely and focus on his own goals, like becoming a better Pokémon trainer. He would also probably have some internal struggles, as he has memories and experiences with these friends that he can't just forget.