The eternal peace of people is threatened by the Millennium Earl, who bonds their souls and turns them in akuma(translated from Japanese “akuma” means “demon”), using the weakness of humans who want to get back their dead beloved ones. Against the creatures akuma are the exorcists of the Black Order. They are chosen by Gods and each one of them is gifted with an “innocence” and the ability to use it as a weapon in the fight against akumas. After fight the soul in every destroyed akuma finds its longed-for peace.
And still the creatures’ akuma are a kind of weapon, and people over and over again use weapons to destroy other humans. That’s similar to the ideology of the Noah clan in the anime. Even though they are humans they work with the Millennium Earl and create more and more akuma creatures. The exorcists destroy only akumas, but would they kill humans (from the Noah clan) if there is no other option?
The plot is getting more complicated and interesting, but I won’t hint anymore. I am leaving each one of you to enjoy the anime.