Percy himself is obviously a very popular character to include since the whole concept of tg (transformation) can be applied to him in many different and interesting ways. His friends like Annabeth are also popular. You can create scenarios where Annabeth has to deal with Percy's transformation and how it affects their relationship.
Grover is another great character. Imagine Grover's reaction if Percy were to be transformed into a completely different creature. Grover could be the one to try and help Percy adapt, or he could be really confused and scared at first. Also, the gods can be included, especially Poseidon. Since Percy is his son, Poseidon's reaction to Percy's transformation would be a key part of the story.
Grover can be a great addition. His ability to sense danger and his connection to nature can be translated into some unique in - game abilities. Also, Nico di Angelo is quite popular. His control over the dead could be a very cool power - up or special ability in the fanfiction's gaming world.
Percy is definitely one of the most popular. Since he's the main character, fans like to explore different versions of him through transformation. For example, seeing him as a different mythical creature or having a different gender can lead to really interesting stories. Another popular one is Annabeth. Her intelligence and strong personality make her a great candidate for transformation. Fans might be interested in seeing how she'd handle a physical or gender transformation. Grover is also popular. Given his satyr nature, there are a lot of possibilities for further transformation, like turning him into a full - blown forest spirit or something more powerful in the nature - related realm.
Pikachu is always a popular choice. It's so well - known and cute, and imagining it in a transformation scenario, like turning into a human or another Pokemon, can be really interesting. Another popular character would be Charizard. Its cool and powerful look makes for great transformation stories. And of course, Mewtwo. Given its mysterious origin and powerful psychic abilities, a TG story involving Mewtwo could be very engaging.
Percy himself is obviously very popular. After all, it's his series. Annabeth is also a fan favorite, as her intelligence and strong will make for interesting storylines. Nico di Angelo is quite popular too, especially when his powers and his somewhat dark nature are explored in fanfiction.
One of the most interesting characters to include would be Hermione from Harry Potter. Her intelligence and knowledge of magic could help Percy and his friends in many situations. Also, Captain America from the Avengers. His leadership and sense of justice would blend well with Percy's own heroic nature. And Clary from the Mortal Instruments, her skills as a shadowhunter and Percy's demigod abilities could create a really engaging story.
Jason Grace is often included. His leadership skills and ability to fly would be useful in various crossovers. In a crossover with the X - Men, he could be seen as a mutant with his flying and lightning powers. Piper McLean is also a favorite. Her charm - speak ability could be very effective in different crossovers. For instance, in a crossover with the world of Game of Thrones, she could use it to manipulate some of the power - hungry lords. And let's not forget Grover. His satyr nature and his loyalty to Percy make him a great addition to any crossover.
Grover is a great character to include too. His connection to nature and his loyalty to Percy make him a wonderful addition. He can provide comic relief at times, but also be a crucial part of the team when it comes to using his nature - based powers to sense danger or find hidden paths.
Aside from Percy, Jason Grace is often included. He has his own set of powers and experiences from being a Roman demigod, which can create great conflicts and alliances in fanfiction. Piper McLean is also a great character to add. Her charm - speak ability can be used in really creative ways in a story. And of course, Leo Valdez with his mechanical skills and humorous personality can add a lot of fun and action to the fanfiction.
Athena is quite popular. She represents wisdom and strategy, so she can add a lot of depth to the story. Percy could learn from her or be in conflict with her plans. Aphrodite is also a favorite. Her domain of love and beauty can create interesting love - related subplots, like making Percy fall for someone against his will or causing jealousy among characters.
Percy Jackson himself is still very popular. People love to write about his further adventures, his growth as a demigod, and his relationships. For example, his relationship with Annabeth might be explored in more depth, like how they deal with new challenges as a couple.