In the depths of Arkham City, Kuro Daijuuji, a destitute detective, receives an intriguing offer from Ruri Hado of the Hado Financial Group: to locate a mystical tome. Initially hesitant, Kuro's resolve crumbles when tempted by a hefty reward. During his quest, he crosses paths with Al, a beautiful girl who harbors immense magical power within her as a potent grimoire. Through a fateful pact, Kuro gains access to formidable magic. Subsequently, they join forces to unleash Demonbane, a formidable deus machina in the group's possession, to combat the technological terror of the Black Lodge. Thus unfolds the epic conflict between the Hado Financial Group and their enigmatic adversaries.