His other Pokémon like Bulbasaur and Charmander would also be startled. They might gather around Ash - Zoroark and sniff him out to make sure it's still him. They could be a bit hesitant to follow his commands at first because they're not used to his new form. However, as they see that Ash's spirit is still there, they would gradually start to trust and follow him again, and they would work together to figure out how to turn him back.
Some of the more intelligent Pokémon in Ash's team, like Squirtle or Greninja, would immediately start to analyze the situation. They would look for signs of what caused the transformation and try to find a solution. They might communicate with other Pokémon in the area to gather information. They would also be protective of Ash in his new form, making sure that no other Pokémon or humans harm him while he's in this vulnerable state of transformation.
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.
Some of his Pokémon might be very confused and sad. Pokémon like Pikachu, who has been with Ash for a long time, would probably miss the adventures and battles they had together. Pikachu might try to cheer Ash up and convince him to change his mind.
Some of his Pokémon like Pikachu might be very protective. Pikachu would stay close to Ash at all times, being extra vigilant in case any danger comes while Ash is in this new form. It would also be curious and might try to play with Ash's new fairy features, like his wings if he has any.
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.
One possible plot could be that Ash is in a strange, enchanted forest. He somehow gets caught in a magical spell that starts to transform him into a Zoroark. As he changes, he begins to experience the world from a Zoroark's perspective. He discovers new powers and instincts, like the ability to create illusions to protect his friends from approaching danger in the forest. His Pokémon friends are initially confused but then realize it's still Ash inside.
His Pokémon would probably be very confused at first. Pikachu, for example, might try to zap Ash back to his senses if he starts acting like a Team Rocket member. They would likely sense that something is wrong with Ash and would do their best to get him away from Team Rocket's influence.
Some of his Pokémon might be confused. Pokémon like Pikachu, who has a very close bond with Ash, would initially be in shock. Pikachu would likely try to understand why Ash is doing what he's doing and might even try to stop him at first.
Some of his Pokémon might sense the change in Ash immediately. Pikachu, being his closest partner, could be both curious and a bit protective. It might stay closer to Ash during battles, as if it knows Ash has a new power to draw from. Other Pokémon like Charizard might be a bit more aloof at first, but as they see the benefits of Ash's aura powers in battles and in protecting them, they would come to accept and rely on it.
Pikachu would probably be very excited. It might jump around Ash, making little electric sparks of joy. Bulbasaur could bring Serena some fresh berries it finds in the forest as a sign of care. Eevee, if they have one, might curl up next to Serena's belly, as if protecting the unborn baby. Their Pokémon would sense the importance of this new development and do their best to be helpful and protective.
Pikachu would be super excited. It has been with Ash for so long and would see Misty as part of the family. It might play more with Misty's water - type Pokémon. Misty's Starmie could be very protective of the new family unit and use its psychic powers to help around the house sometimes.