This story takes place in a world in which the demon gates have opened and destroyed just about every human being on the planet. Demons walk with the living. What humans are left are either hiding or fighting. Some have taken upon themselves to learn Demon Artifacts and mastered using them, and gained the names of "Witch".
The story revolves around Bleu, a hate-child (human mother, demon father) who is looking to kill Lucifer, but is told Lucifer is already dead. She walks the world in search for the truth. There is a strong cast of people and their paths that will cross on many occasions.