You could have an OC who is a librarian in the Inkheart world. This librarian has a secret collection of books that are banned because they contain dangerous magic. The OC gets involved with the main characters when they discover that some villain is after these books. Another idea is an OC who is a painter that can bring paintings to life, similar to how characters are brought out of books in Inkheart. This OC could get into trouble when one of the painted characters turns out to be evil. And a final idea might be an OC who is a messenger between different magical worlds. They come to Inkheart's world to deliver a warning about an approaching threat that could endanger all the book - related magic.
Well, you could write a fanfiction where the Inkworld is slowly being corrupted by a new form of dark magic. The characters have to find a way to stop it by traveling to the very source of magic in the Inkworld. Another idea is to write from the perspective of Capricorn's henchmen. What were their thoughts and feelings while serving such an evil master? And then there's the idea of a fanfiction that focuses on the power of words in Inkheart in a different way. For instance, a character discovers that they can create new things by writing their own special words, not just reading things into existence.
One idea could be creating an OC who has a unique power related to time manipulation. They could be from a different dimension and end up in the Avengers' world. Another idea is an OC who is a master of ancient magic and teams up with Doctor Strange within the Avengers group. Maybe an OC that is a super - intelligent android created by a villain but has a change of heart and joins the Avengers.
You could create an OC for your Persona OC fanfiction who is an artist. This artist OC could use their art as a way to understand and even manipulate the Metaverse. For example, they might draw scenes from the Metaverse that give clues about upcoming events or hidden locations. Their art could also be a form of therapy for other characters who are struggling with their dual lives in the real world and the Metaverse.
Perhaps an OC who is a half - human, half - beast creature. This OC could struggle with acceptance in both the human and beast - kin societies. They end up meeting the main characters during their adventures and learn to embrace their unique identity with the help of the group, while also adding their own combat skills, which are a blend of human strategy and beast - like strength, to the team.
One idea could be to explore the Riddler's origin story from the perspective of your original character (OC). Maybe your OC is a detective trying to solve the mystery of the Riddler's first crime spree. Another idea is to have your OC be a sidekick of the Riddler, either willingly or by being forced into it. They could then have a complex relationship where the OC tries to influence the Riddler's actions for better or worse.
One idea could be an OC who is a brilliant scientist in the Fallout world. They could be working on a secret project to reverse the effects of radiation. Another idea is an OC who is a wandering trader, having all kinds of adventures while traveling from one settlement to another, facing raiders and mutants along the way. And a third idea could be an OC that is part of a new faction trying to bring peace and order to the wasteland.
You could also create an OC human who discovers a hidden talent for communicating with trolls through music. In the fanfiction, this character could use their musical ability to bridge the gap between the two worlds, maybe even creating a new form of harmony between trolls and humans that was previously unthinkable.
One idea could be to create a story where your Bratz OC is a new student in Stilesville. She has a unique fashion sense that both confuses and intrigues the other Bratz girls at first. As the story progresses, they become friends and she helps them design a whole new line of clothing for an upcoming fashion show.
One idea could be creating an OC who is a transfer student with a unique past related to the Dark Hour. For example, they might have had a family member affected by Shadows long before coming to the school. Another idea is an OC with a special ability that doesn't quite fit the normal Persona - using skills that are more about mental manipulation rather than direct combat. And you could also have an OC who is initially a skeptic about the whole Persona thing but slowly gets drawn into it.
One idea could be creating an OC who is a new recruit in the Hellsing Organization. They could have a unique power, like the ability to control shadows, which adds an interesting dynamic to the battles against vampires. Another idea is an OC that is a vampire with a conscience, struggling between their blood - thirsty nature and the human values they still hold. This can create complex moral dilemmas within the Hellsing universe.