They are the Dark Clerics of the Black Order, exorcists with supernatural abilities...
Long, long ago, the Millennium Earl tried to take over the Earth. Someone used the power of God to destroy him, and peace returned to the world. But a prophecy foretold that the Millennium Earl would come again.
Now the Millennium Earl has returned, turning the souls of the dead into demons in his bid to conquer the world. But the people turning those souls into demons are the ones closest to them! They don't mean to turn the dead into demons. They're simply lost and believe the Millennium Earl, thinking they can bring their loved ones back to life. But not only can they not revive them, they turn them into demons, into weapons of the Millennium Earl... Those are the Akuma!
Everything changed after someone discovered a stone box!
There are messengers chosen by God who can destroy demons. Their organization is the Black Order! Its Dark Clerics are known as Exorcists... Armed with anti-demon weapons imbued with supernatural power, they will change everything... They are the Millennium Earl's natural enemies.
P.S. Updates are irregular, and I'm revising the story.