Basilisk: Kouga Ninpou Chou, X Recommendations
Both Basilisk and X have two waring factions with supernatural abilities, they also don't have your typical moral "good" and "bad" sides. Both animes also have a somewhat bleak atmosphere to them, and contain a similar group combat progression (deliberated phrased strangely to avoid spoilers). Both these animes also leave a bit to be desired from their leading characters, but have relatively solid supporting characters. However these two animes are set in different time periods, and also have a different feel to them.