His friends, like Misty and Brock, would be very supportive. Misty might be a bit more straightforward and tell him to snap out of it, but also offer kind words. Brock, being the more nurturing type, could cook him a special meal or give him some advice based on his own experiences. They would all rally around Ash to lift his spirits.
His Pokémon might try to cheer him up. Pikachu, for instance, could use its cute antics to make Ash smile. It might nuzzle against him or do some of its signature electric tricks in a playful way. They have a very close bond, so the Pokémon would sense his sadness and do their best to make him feel better.
His friends like Pikachu would be very worried. Pikachu would probably stay by Ash's side, trying to use its electric shocks gently to revive him. Misty might scold Ash for being so reckless but also show concern by getting water to cool him down. Brock would immediately start checking Ash's vital signs and try to figure out what went wrong.
Pikachu would be very worried. It would stay by Ash's side constantly, using its electric shocks to keep him warm if he has a fever. His other Pokémon like Bulbasaur might use its vines to bring water or herbs to help soothe Ash's symptoms. Charmander could use its fire to keep the area around Ash cozy.
One reason could be that he lost a really tough Pokémon battle. Losing can be a big blow to his confidence and make him feel down. Maybe he was facing a powerful opponent he had been preparing for a long time, and the defeat made him question his skills as a Pokémon trainer.
Pikachu would probably be very curious. It might zap the lightsaber a bit to see what would happen, and then be in awe of the bright blade. It could also get a bit protective of Ash when he wields the lightsaber, as if it senses the added danger.
At first, Ash would be in shock. But then, he would likely turn his focus on finding out the truth. He's not one to give up easily. He'd start investigating what led to his betrayal. He might even go on a journey within the RWBY world to find evidence to clear his name and expose those who really are at fault. He'd still hold out hope that his former friends would see the truth and come back to his side.
Some characters might be very worried and rush to his aid. Others could see it as an opportunity to gain power or influence in his absence.
Kagome usually gets very worried. She'll immediately try to use her spiritual powers to heal him if she can. If not, she'll search for herbs or other ways to help. Miroku would likely offer his support in a more practical way, like finding a safe place for Inuyasha to rest. Sango might be on guard, making sure that no more enemies take advantage of Inuyasha's weakened state.
Some characters might be shocked. They could never have expected Dexter to be involved in such situations.
Harry would probably be extremely worried. He'd immediately rush to her side, trying to figure out how to help. Ron, on the other hand, might be in a bit of a panic at first but then would do whatever he could to protect her while waiting for help. Hagrid might bring some of his home - made remedies, thinking they could work on her injury.
Pikachu would probably be very protective. It might zap anyone who tries to make fun of Ash. Misty would likely be shocked at first, but then she'd start taking care of him like an older sister, making sure he's clean and fed. Brock, being the nurturing type, would probably be the one to find practical solutions for taking care of baby - Ash, like finding proper diapers in the Pokemon world.