Kuro Daijuuji, a penniless detective living in Arkham City, is approached by Ruri Hado of the Hado Financial Group to locate a powerful magic book. Though he initially refuses, a large payment convinces him to accept the job. While searching, Kuro encounters Al, a striking young woman who is actually a powerful grimoire. The two form a contract, granting Kuro access to formidable magic. Soon after, Al activates Demonbane, a deus machina owned by the Hado Financial Group, to fight the mechanical threat posed by the Black Lodge, sparking a war between the Hado Financial Group and the Black Lodge.