Shingeki no Bahamut: Genesis
The story first starts off around Favaro Leone who is a bounty hunter, collecting money off of bounties he collects (demons). 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.
Season:
1