One idea included some kind of romance, which made me gag and want to run away. I'm just not that good with romance as the main plot. As a tiny subplot, I can just about manage some attraction -- sometimes.
Other ideas have included a much too passive heroine -- also a big turn-off. She has to be actively involved in the resolution of the story, not just sit there and let events wash over her. Everybody writes about mermaids, nobody writes about the rocks in the sea. Why? Because they don't do anything -- they're boring! But whenever I want to think about "and then what happens?" nothing comes to mind.
I've thought of some what-if situations that are much too complicated for me to grapple with (what if you found out that what you thought was a super-computer was really a god?) And some of my what-if situations have led down paths that end on a negative note. Not what I was looking for, this time around!
I was going to write that there is a difference between writing fanfic and writing "regular" stories, but then I realized there really isn't. Yes, in some fandoms, you have a basic plot structure that you can use. In Spooks, for instance, the MI-5 agents should always be ready to sniff out and hunt down terrorists, spoiling their dastardly plans at the last minute. In Harry Potter, the threat of Voldemort is forever looming in the background. In Star Wars, the Dark Side always beckons. And there are all those cop and forensic procedurals where crimes must be solved by various methods. But you don't have to use those conflicts, you can take your characters away from all that and have them do something during their time off. Regular stories are just the same; you can use any plot you want. You can even borrow one from a fandom -- under a different name, of course.
I guess the only solution for me is to keep brainstorming, and eventually I'll hit upon an idea that sounds right, which I can deal with, and which has a happy ending. (And maybe, if it grows naturally, even a little attraction.)
Now, if I were going to take my original characters and combine them with a plot from a fandom, which fandom would I choose, and which plot?
Wait a minute, isn't that the question that started it all? I'll have to get back to you on this.