I find myself stumped by the first part of this question. How many characters do I write regularly? How many original characters have I created? (Answer: probably dozens; I find it hard to write in someone else's universe without populating it. The world would be awfully empty if I stuck to writing solely canon characters.) So, a lot?
If the question is whether there are certain characters I keep coming back to, the answer is certainly yes. In FFX, my "home" characters, and the ones I'm most comfortable writing, are Auron, Paine (with and without Nooj), and Baralai; in FFXII, so far they appear to be Ashe and Balthier, separately and together. It seems to be the case, so far, for me, that the hook to get me into writing for a fandom is a character. I latch onto a character (and/or a pairing), and I want to know more about them, or I have an idea about where to take them next, and I start rolling. My writing is, was, and probably always will be character- rather than plot-driven, which is part of what I like so much about writing fanfic: I can focus on character studies and let the plot take care of itself.
As for writing men versus women, I think my work is fairly balanced on that score. I am, as fandom defines these things, a writer of mostly het and gen, and that requires me to write men and women both. (Note that the "home characters" list contains two women and three men, and given the gender balance of characters in the source material, I don't think that's too bad.) If I had to pick, I would probably say that I am slightly more comfortable writing women, but the difference is slight. For me, it depends a lot more on the individual character: some are easy to write, some are like pulling teeth, although I get more comfortable with time -- Gippal, to pick one example, used to give me headaches to write, but now his voice comes much more easily to me. Yuna, too. Like everything, it takes practice.
30 Days of Writing: Complete list of questions
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