Mistarcia is a magical world where humans, gods, and demons mingle together. In the past, the black-and-silver winged Bahamut has threatened to destroy the land, but humans, gods, and demons overcame their differences to fight together and seal its power.
The key to that seal was split in two, one half given to the gods and the other to demons, so that they would never be united and Bahamut never released. Now, two thousand years later, the world is in an era of peace—until the day a human woman steals the gods’ half of the key.
The story first starts off around Favaro Leone who is a bounty hunter, collecting money off of the demons he captures. He is also seen as a rebellious degenerate who spends his money of alcohol and women. Favaro Leone soon runs into Amira who has no clue what is really going on besides the fact that she must go to “Hellheim”, a place where she can go meet her mother. Favaro Leone is then dragged onto this whole quest with her because she had cast a “contract spell” where he now has a demon tail and the only way to get it off is by completing his side of the deal.