Twins? The thought had crossed my mind. I didn't know how to pull something like that off without seeming too cliched. That doesn't just happen in anime, either. Lots of sci-fi things will have a sort of Gemini thing going on, too.
I really don't have room for something like that in the existing stories, either. It'd be too hard to work that in. I could try to fit that into either the 4th or 5th stories I have ideas for.