One idea could be a Pokemon that can shapeshift into different legendary Pokemon to gain their powers. For example, it could shift into Mew to use its psychic abilities in unique ways. Another idea is a shapeshifting Pokemon that disguises itself as other common Pokemon to play pranks on trainers. It could be really fun to write about the chaos it causes.
A unique character in a Pokemon shapeshifter fanfic could be a shapeshifting Pokemon that has a special bond with a particular trainer. This Pokemon can only fully control its shapeshifting ability when it's with that trainer. The trainer could be from a family with a special history related to Pokemon shapeshifting, and together they embark on a journey to discover more about this ability.
Charizard is another one. A Charizard shapeshifter can bring in a lot of cool elements. It can be a powerful and intimidating presence, and when it shapeshifts, it might gain new abilities or appearances that are both fascinating and fearsome.
One idea could be a pokemon shapeshifter that is trying to hide its true form in a human - dominated city. It has to constantly adapt and learn human behaviors to avoid detection.
One plot idea could be Ash getting the ability to shapeshift accidentally. For example, he touches a strange Pokemon or an ancient artifact. Then he has to figure out how to control this new power while on his journey to become a Pokemon master. Another idea is that an evil organization wants to use Ash's shapeshifting ability for their own nefarious purposes, so he has to avoid them and protect his friends.
One common theme is identity. Since the character can shapeshift, they often struggle with who they really are. Another theme is power and its consequences. Shapeshifting is a powerful ability and fanfics often explore how it can be misused or how it attracts unwanted attention.
Obviously, Ash's main friends like Misty and Brock would be involved. Misty could be the one who first notices Ash's strange new ability and helps him keep it a secret at first. Brock, with his knowledge of Pokemon, could try to figure out how to reverse the shapeshifting if it becomes a problem. Also, Team Rocket would be great characters in this. They could constantly be trying to capture Ash in his different shapes, thinking they've discovered a new and valuable Pokemon.
Well, a major theme is the exploration of new powers. Shapeshifting is a unique ability, and in these fanfics, we often see the characters discover the limits and potential of this power. They might experiment with different forms and how each form can be useful in different situations. Also, friendship is a common theme. The shapeshifter forms bonds with Harry, Hermione, Ron and other characters, and these relationships are developed as they face challenges together, like dealing with dark wizards or solving magical mysteries.
I really like 'A Shapeshifter's Tale in Black Butler'. This fanfic focuses on the reader's character development as a shapeshifter. It starts with the reader being confused about their powers and gradually finding their place in the Black Butler universe. The relationships with Sebastian and Ciel are also well - written, adding depth to the story.
Another theme is secrecy. Shapeshifters usually have secrets, like their true form or their real motives. In fanfics, this creates a lot of suspense. They might be hiding something from Sebastian or Ciel, and as the story progresses, these secrets are gradually revealed, adding to the intrigue of the plot.