One idea could be an OC who has the power of music in the Precure world. She could use melodies to heal or empower others. Another idea is an OC from a different dimension who comes to the Precure world with unique powers and has to learn how to fit in and fight alongside the Precure. Maybe an OC that is half - human, half - magical creature and has to hide her true identity while being a Precure.
An interesting Precure OC fanfic idea could be an OC who is a transfer student to the school where the Precure are. This OC has a secret past related to the villains and gradually discovers her own power to become a Precure. Also, an OC with the power of time manipulation in the Precure universe would be cool. She could freeze time to prevent disasters or rewind time to correct mistakes made during battles.
One idea could be creating an OC who has the power of music in the Precure world. They could use melodies to heal and fight against the villains. Another is an OC from a different dimension who stumbles into the Precure universe and has to learn their ways to help. And also, an OC that is a hybrid of a magical creature and a human in the Precure world, bringing unique powers and a fresh perspective to the story.
A time - travel plot in a Precure All Stars fanfic could be really cool. Maybe the Precure travel back in time to the origin of their powers and have to make sure that the events that led to their powers being created happen correctly. It could involve meeting their predecessors and learning about the true nature of their powers.
One popular idea is an alternate universe where the Precure characters have different powers or backstories. For example, they could be in a steampunk world. Another idea is a crossover with other popular magical girl series. This can bring new and interesting dynamics. Also, a fanfic about the Precure's daily lives outside of their heroic duties, like going to school or dealing with family, can be quite engaging.
To start writing a Precure OC fanfic, begin by brainstorming your OC's powers. If they have the power of light, consider how that power will be used in battles and how it might affect their relationships with the other Precure. After that, establish the setting. Is it in the same town as the original Precure? Or a new location? Then, write a rough outline of the story, including the introduction of your OC, the conflict they will face, and how they will resolve it.
A great plot could be that the Precures lose their memories but still feel a strong urge to fight evil. They would have to figure out who they are and what their powers are while still protecting the world. Or, you could write a fanfiction where a new villain emerges who can control the stars in a different way than the previous ones. This would force the Precures to come up with new strategies to defeat the villain.
One idea could be a crossover with another magical girl series like Sailor Moon. The Smile Precure girls could meet the Sailor Scouts and they team up to fight a common enemy that threatens both their worlds. Maybe they have to combine their powers in new and unexpected ways.
An interesting MCU OC fanfic idea could be an OC who is a journalist. They are always on the hunt for the next big story about the superheroes. This could lead them into all sorts of dangerous situations as they try to get exclusive interviews or expose secrets. Another could be an OC who is a mutant in the MCU (even though mutants are not as prominent yet). This OC would have to deal with being different and feared, while also trying to use their powers for good. And a third idea is an OC who is a reformed villain. They were once on the wrong side but now want to make amends and help the heroes in their fight.
A Sonic OC fanfic could center around an OC who is a healer. In a world full of battles against Dr. Eggman, this OC would use their healing powers to patch up Sonic and the gang after tough fights. They could also have a backstory about how they learned their healing abilities, maybe from an ancient and forgotten tribe in the Sonic world. This would add depth to the character and the fanfic as a whole.
You could write an OC fanfic where the OC is a female assassin. She has a rivalry with Agent 47 at first, thinking he is taking all the good contracts. But as the story progresses, they end up having to team up to take down a powerful criminal organization that is targeting assassins. Her special skill could be hacking into high - security systems to gain access to targets.
A Hiccup OC fanfic could also explore what would happen if Hiccup's OC was from a different tribe. They could have different traditions and skills, and the story could focus on how Hiccup and his friends learn from this new character. For example, the OC could teach them a unique way of dragon training that they've never seen before.