One popular place to find 'ash and may body swap fanfiction' could be Archive of Our Own (AO3). There are likely many stories there that explore this interesting concept. You can search for the relevant tags like 'Ash Ketchum', 'May', and 'body swap' to narrow down the results.
Pikachu might be very confused at first. When it sees 'Ash' (really May in Ash's body) acting differently, it could be hesitant to follow commands as usual. For May's Pokemon, they might be surprised to see 'May' (Ash in May's body) suddenly having a more battle - oriented attitude. For example, May's Beautifly might be confused when 'May' wants to train it for battles instead of focusing on its appearance for Contests.
One interesting plot could be that Ash, now in May's body, tries to enter a Pokemon Contest. He has to quickly learn the skills and grace that May has, like how to style the Pokemon in a more appealing way for the judges. Meanwhile, May in Ash's body decides to enter a Gym battle. She struggles with Ash's more straightforward and battle - focused approach compared to her Contest strategies.
One interesting plot point could be how they adjust to each other's abilities. For example, Ash suddenly having to deal with May's knowledge of Pokémon contests, and May having to handle Ash's battling skills. Another could be the reactions of their friends and Pokémon. Their Pokémon might be confused by the sudden change in their trainers' behavior.
Adaptation is also a big theme. Ash has to quickly adapt to the new body's abilities, limitations, and sometimes even different personalities. This can range from getting used to a new physical form in a body swap with a Pokémon, to dealing with the different skill sets of another trainer in a human - human body swap. It's all about how he copes and thrives in the new situation.
Another theme is relationship exploration. This body swap situation can bring out different dynamics in their relationship. For example, they might understand each other's feelings better. Also, there could be a lot of humorous situations as they try to navigate the world in each other's bodies. They may struggle with things like how the other behaves in certain situations or how to interact with their Pokémon in a different body.
Another theme is adaptation. Ash has to quickly adapt to the new body's physical abilities, like different levels of strength or agility. This often leads to some really interesting scenarios where he has to figure out how to battle or move around in a completely different way. For example, if he swaps with a smaller trainer, he might have to find new strategies for catching Pokemon. Also, there's often the theme of friendship. His friends might not recognize him at first, and he has to prove that he's still Ash on the inside, which shows the strong bonds of friendship in the Pokemon world.
Perhaps a major plot twist could be that the body swap is not accidental but part of a bigger plan by a mysterious villain. This villain could be using their body swap to gain access to something that only Ash or Iris can reach in their normal bodies. For example, there could be a special Pokémon or a powerful item. And as they try to figure out how to swap back, they also have to deal with this new threat, which adds a whole new layer of complexity to the fanfiction.
Yes, there are quite a few. You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Some stories might focus on how Ash and Nurse Joy deal with the swapped bodies, like trying to carry out each other's daily tasks in a humorous way.
One popular 'ash body swap fanfiction' is 'Swapped Worlds' which has an interesting take on the body swap concept involving Ash. It plays with different Pokémon interactions in the swapped state.