Ruby would be excited. Yang would find it cool. Weiss might be a bit skeptical at first, but Blake could see the potential for interesting stories.
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.
Well, I think some of the characters might be really flattered. Ruby, for example, would probably be super excited to see how fans are inspired by the music in the RWBY world and create stories around it. She loves the positive energy and creativity that comes with 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.
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.
In 'rwby watches earth fanfiction', Ruby would be wide - eyed and eager to explore every new thing. She'd be constantly asking questions about how things work. Weiss would be shocked by the lack of a Dust - based power system but would soon start to admire Earth's ingenuity. Blake would be drawn to the underground subcultures on Earth, like punk or goth cultures. Yang would be amazed by the variety of fighting styles on Earth, from martial arts to boxing. They all would have to come to terms with the fact that Earth is a very different place from Remnant.
Ruby would be really excited. She loves stories of heroism and the fanfiction would likely be full of that. Weiss might be a bit more reserved, but still intrigued. Blake would be drawn to the deeper themes and how they're presented. Yang would probably be shouting at the exciting parts.
Some might be amused. Naruto characters have their own set of stories and adventures, and seeing the different and often wild ideas in RWBY fanfiction could be a source of entertainment for them.
Ruby might be a bit shocked at first, but then she'd be really intrigued. She's always open to new ideas and would probably try to find ways to apply what she reads to her own life in Remnant. Maybe she'd start thinking about how to better protect her friends from potential disease threats.
He'd probably be very curious. Naruto has always been eager to learn about new things, and RWBY fanfiction would be a whole new world for him to explore.
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.