Confession: when my brain isn’t occupied with other things, I spend an insane amount of time maneuvering my mental avatars through other peoples’ fictional worlds. Worlds that contain a favorite character - especially one on whom I have a crush - are frequent destinations.
I end up building intricate cannons around my original characters, weaving them into the other characters’ backstories, and creating a cannon-compatible origin and role for them to occupy.
They make enemies, they make friends, they make new plot threads… and in the cases of my favorites, it’s only a matter of time before something wonderful and terrible happens:
They outgrow their roles as roleplay characters, and demand a story of their own.
And it makes me sad to think of it staying forever trapped inside my head, unable to escape onto the pages of a book where it belongs.
At that point, fanfiction is an option. Sure, that would create the potential for accusations of Mary Sues, but my characters are always flawed and unpopular enough to make such complaints irrelevant, so that isn't really a factor.
But sometimes, I simply like the whole thing too much. The original character is too complex, the relationships too interesting, the additions to the backstory too intricate, and the new plot threads too big to relegate them to the realm of fanfiction.
At that point, I’m faced with a choice: whether to leave the story locked in my head, to settle for writing a fanfiction, or take on the challenge of extracting the aspects of the world, characters and relationships that make the story work, and making them my own.
I usually go for the last one.
The process is never instantaneous. It takes time to let go of the parts of the story I don't own, and for the parts that are original to me to flesh themselves out and learn to stand on their own two feet, separate from their parents.
But when you're really in love with a story you've made, it's always worth the effort.