A wager. A wager made by Mephisto Pheles to see if Rin Okumura would become a Demon Lord or the Greatest Weapon for Humanity. A wager no one in the Vatican would take. A wager only a Vampire Slaying Protestant Woman would agree to. Facing death at the hands of the Vatican and the exorcists Rin desired to be a part of, his only option is this British Noblewoman and her Red Clad Familiar. . .