Kurou Daijuuji is a low-level investigator in Arkham City. Ruri Hado of Hado Financial Group asked him to look for a magic book one day. While he originally declined, Ruri bribed Kuro by offering him a substantial quantity of money upon accomplishment of her request. Kurou comes upon Al, a gorgeous female who is actually a strong grimoire, while looking for the book. They form a pact with each other, conferring immense powers on Kuro. Soon after, Al summons Demonbane, a deus machina owned by the Hado Financial Group, to battle the mechanical threat posed by the Black Lodge. The conflict between the Hado Financial Group and the Black Lodge has begun....