Haha, yes, Oni was a VERY late addition into the story. I was actually in the bathroom during my break, trying to figure out how Koh got started stealing faces. I'd already decided that the epilogue would feature Koh's successor walking out and seating himself on his throne, but not any tie for that successor to the existing story. Then I decided, hey, Koh swapped faces with some dude for kicks, and then left his behind. It wasn't a hard jump from there.

As for what's next...well, I can't promise that it'll come any time soon, but I do have an idea in mind for an AU fic involving Sokka and Yue. (Oh Sokka. Why do I write so much AU fic for you? i never wrote AU fic before you!)