twinkledru was
thinking about Mary Sue, and
loligo asked about
original character romances. I've said what I have to say about both of these issues more than once, but I did start thinking a bit about writing. In fact I started thinking about putting my money where my mouth is and writing a story with a main character OC.
The first story I finished and posted was a Krycek/OFC romance. Well, romance might be pushing things -- the conspiracy was the A-plot -- but they did have sex. Twice, which may be a record for Krycek in my stories. (Alex Krycek: killing people to avoid thinking about his sexual frustration in Vanzetti's stories since 1999.) Anyway, it struck me as a reasonable thing to do; I don't really buy the idea that Krycek's primary emotional ties are to Mulder or Scully, and we see so little of the character that it seemed logical to me that he'd have some life beyond what we saw in the show. I started to consider what that life might be like and the next thing I knew I had a handful of original characters and a moderately plausible backstory. I'm still fond of those stories, but I'm not sure I want to go back to them; every now and then I think about transposing the OCs to an Alias story or an Alias/XF crossover, probably without the romance. And since then I've moved away from writing main character OCs. I do write crossovers, and I find it interesting that for some readers, a crossover might as well be an OC story -- I know that not all the people who read my crossovers know both fandoms. And crossovers do some of the same work that main character OC stories do, as well: they shed new light on and provide new context for the canon characters. But since one of my problems with the term "Mary Sue" is that it discourages more experienced writers from writing main character OCs and especially OC romances, I feel vaguely guilty about neglecting the genre in favor of the crossover. In XF, my interest shifted to the Krycek/Marita relationship, and then XF canon happened, and I still have issues. Someday, though. I'm going to write my grand unified theory of Sark story, and that's going to need OCs -- the difference is that Sark needs to form associations with characters outside of canon because he needs to get away from the Bristow-Derevko nexus of doom if he's ever going to become an independent person. Provided he survives the end of the series, at any rate. And I'm not entirely sure what kind of character and situation would best allow him to separate himself from the canon characters.
This was going to be a long post about the kind of canon characters for whom it's easiest to imagine an OC romance, but I got tired, and I expect that you can all fill in the blanks from what I've written above.