-Blue Exorcist
Well, it has blue flames and has demons in it '_' Though I personally read Code Breaker and has never watched it so I'm not too sure about my recommendations xD
-Darker Than Black
One of my all time favs, similar plot about a crime syndicate with super-natural powers. It has a dark tone, however sometimes it seems to be rather cheerful. The episode follows the everyday life of an agent with the code name, Hei. The real plot doesn't really show up until the end, though is hinted throughout the series. Now that I think about it, it's actually REALLY similar so yea... '-'
PS: DON'T WATCH SEASON 2, PERIOD.
