How about thriller? I know it's horror sub genre but they're totally different. Also, I would love to have a psychological and tragedy genre too if it's possible, just to widen the search.
And probably wasn't that popular, but, historical and school life.
And yay for multi genre!
*edit. I just though of a genre that's pretty much available on the free to read but garner no much mention, and that's fan fiction and fan comic. I know you didn't particularly allow it but I wonder if you made a genre for that and if the author clicked to have that genre, they knew that their ad revenue can't be activated but there support will still be available (since that's what Michael said). Not sure how you'll see this but I think it's good to have that.