 If you liked D.Gray-man |  ...then you might like Enen no Shouboutai |
Finding the similarity in the plot, where both protagonists share a similar childhood trauma, one fights the demons, and other as firefighter fights people turned to fire demons
report Recommended by Billy_Babic
Both of these are enjoyable battle shounen with great main characters who happen to share similar backstories and circumstances and are part of organisations that put former humans turned monsters to rest. They also feature extraordinarily mysterious villains and the more you delve into spoiler territory, the more additional resemblances you find.