I’ve written quite a lot of fanfic, and wrote an article about it earlier this summer for an online zine that addresses what, for me, is the appeal of playing with other people’s characters. I wrote the article particularly about slash, but the main points apply just as well to non-erotic fic as well.
The fun of fanfic writing for me is seeing what I can do with the characters and settings as established by the canon sources without taking them too far from the source. When I write a story, I think in terms of “possible scenarios” and “character parameters.”
The first is a sort of “what if…” speculation on some event that happened in the book, movie, TV episode, or whatever, and spinning it out in another direction to see where it goes, and see if I can get a story idea out of it. The same point of departure can lead to multiple story ideas, depending on how that “what if…” gets spun out.
The second is a way I use to limit how far can I take my chosen characters while still keeping them identifiable and making what they do in a story seem plausible. I ask myself “How might this person behave in a given hypothetical situation?” and then see what works from there. If I can’t see them doing it, I can’t write it (except maybe as parody or something else bizarre).
That’s the game for me, and that’s where the chief fun of writing fanfic lies. (There’s also the fun of getting feedback and fan letters about my stories, but that’s more of a reason for posting stories online than for simply writing them; I wrote in notebooks for years before I discovered the slash community or there was even an internet to share stories on.)
Writing about my own characters is another type of exercise entirely, since I’m the one who’s creating them, establishing who they are and what they’ll do, and setting up the situations in which they will act. I can still play “what if” and “what would X do here?” with my own characters while I’m working on them, but I have to pick one outcome if I’m going to finish the story.