Team Rocket could be the main antagonists. They might see Ash's transformation into Mew as a way to capture a powerful Pokémon - like being. They could devise all sorts of plans to catch him, thinking that they can use Mew - Ash's powers for their own evil purposes.
Well, if Ash were to turn into Mew in a fanfiction, it would be quite a wild turn of events. Mew is known for its ability to transform and its vast psychic capabilities. Ash, with his new form, could potentially travel to different dimensions that were previously inaccessible. He could also communicate with Pokémon in a whole new way, using Mew's psychic powers to understand their deepest thoughts and feelings.
One idea could be that Ash is on an adventure in a mysterious forest when he encounters a strange, ancient power. This power gradually transforms him into Mew. As Mew - Ash, he discovers new abilities like shape - shifting into different Pokémon forms to communicate better with them and understand their world more deeply.
Well, perhaps Ash could be transformed into a Mew through some magical encounter. He might then use his new form to explore the Pokémon world in ways he couldn't before, like flying high above the clouds and seeing the landscapes from a whole new perspective.
Maybe in the fanfic, a mad scientist creates a device that accidentally swaps Ash's essence with Mew's. As Mew - in Ash's body - Ash has to figure out how to reverse the process while also dealing with Team Rocket, who notice something very strange about 'Ash'. Meanwhile, the real Ash, in Mew's form, tries to use Mew's abilities to stop the scientist from causing more chaos.
Maybe a powerful and envious Mewtwo could be the antagonist. Since Ash has now become a Mew, Mewtwo might feel threatened or think that Ash doesn't deserve such power. So, Mewtwo could try to fight Ash to prove his own superiority.
First, do your research on both Ash and Mew. Know their personalities, abilities, and storylines in the Pokémon universe. For example, Ash is a determined and kind - hearted trainer, while Mew is a rare and powerful psychic Pokémon. Then, come up with a unique plot. It could be something like a magical accident that causes the transformation. Next, focus on how Ash would react in Mew's body. He would likely be both excited and a bit scared at first. Use vivid descriptions to bring the story to life, like describing how it feels for Ash to fly as Mew or use its psychic powers. Also, don't forget to include other characters' reactions, such as Pikachu's confusion or Misty's shock.
Pikachu would most likely be there. Since Pikachu is Ash's closest companion, it would be involved in any story related to Ash. Maybe Pikachu could also have some sort of interaction with Mew, like being a bit jealous at first of Ash's new connection with Mew.
There are a large number of Pokémon fanfics, and the popularity of 'ash is a mew fanfic' would depend on various factors. If it has been well - promoted within Pokémon fan communities, or if it offers a really unique and engaging take on Ash and Mew, it might gain a following. However, if it's not easily discoverable or if the writing quality isn't great, it may not be very popular. So, in short, we can't really determine its popularity just from the title.