In fanfiction where Ash Ketchum gets sick, how do his Pokémon react?

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.

His friends would most likely be very worried. They would gather around him, trying to figure out what was wrong. Percy might use his water powers to cool Leo down if he had a fever. Annabeth would be researching in the library, looking for any information on demigod illnesses. Hazel could use her powers to sense if there was any dark magic involved in Leo's sickness.

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.

The Pokémon might initially think it's some sort of joke or mistake. But as time goes on, if Ash seems serious about being with Team Rocket, they could become divided. Some of the more headstrong Pokémon might leave Ash, while others might stay with him out of loyalty but still be unhappy about the situation. They would be constantly trying to nudge Ash back to his old ways of being a good Pokémon trainer.

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 Ash's Pokémon could try to communicate with the Pokémon center staff or his friends about Ash's condition. They might use their unique abilities to convey how Ash is feeling. For example, if Ash is in a lot of pain, Psyduck could use its psychic powers (even if they are a bit wonky) to show the others that Ash needs more pain relief. This shows that they are not only staying with Ash but also actively trying to help in any way they can, which is a great display of loyalty.

In most 'Naruto gets sick' fanfics, his friends are very concerned. For example, Sakura will immediately start using her medical skills to diagnose and treat him. Sasuke, although he may not show it outwardly as much, will stay by Naruto's side and keep a watchful eye. Shikamaru might come up with plans to make Naruto more comfortable during his illness. And Hinata, she would be really worried and would probably bring Naruto some home - cooked food to help him regain his strength.

Their Pokémon might be very protective. For example, Pikachu could stay closer to Serena all the time, sensing the new life. Some Pokémon might bring small items like berries or soft leaves, thinking it could be useful for Serena or the baby.

The Pokémon community around them would probably be quite shocked at first. Their friends like Brock might be both surprised and happy for them. However, some of the more traditional Pokémon trainers might frown upon it as they are quite young. But Ash's close friends would most likely support them and help them out, like providing a place for May to rest during her pregnancy.

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.