Of course, the God King has been in seclusion for a long time, and it's obvious that not just anyone can seek the God King's Blood, as that would defile the great God King.
So, it seems that the Angel Witch clan once had a Holy Grail of Divine Blood. They publicly claimed that it was a reward from the God King, and that the blood in the Grail was inexhaustible, refilling immediately after a sip.
If a witch drinks the divine blood from that chalice, her magic power will significantly increase, and she will receive the God King's blessing. If an Exotic drinks it, they will transform into a witch.
However, with the decline of the Angel Witches and the rise of the Dragon Witch, the Holy Grail apparently ended up in the hands of the Dragon King. Those Exotic knights probably became witches by drinking the God King's Blood.
As for now, it seems the Holy Grail is in the hands of the Devil King, but Artie is using it as bait for fishing.
