Storyline
Kurou Daijuuji is a poor private detective living in Arkham City. Despite his difficult circumstances, he accepts a highly paid assignment from Ruri Hadou, the young leader of the Hadou Financial Group, to locate a mysterious magical grimoire.
His search eventually leads him to Al Azif, a mysterious girl who is actually the physical manifestation of the Necronomicon. After the two form a contract, Kurou gains access to powerful magic and becomes involved in the struggle against the Black Lodge.
When the Black Lodge launches another attack using its mechanical weapons, Al activates Demonbane, a powerful Deus Machina created to combine the abilities of a Magius with the power of a grimoire. Kurou becomes its pilot, placing himself directly in the middle of the growing war.
As Kurou and Al fight increasingly powerful enemies, their investigation takes them beyond ordinary crime and into a world of ancient grimoires, forbidden sorcery, mysterious organizations, and beings connected to the Cthulhu Mythos. Meanwhile, Ruri and the Hadou Group attempt to protect Arkham City while uncovering the Black Lodge's larger plans.
What begins as a simple detective job gradually develops into a massive supernatural conflict. Kurou must master Demonbane and confront enemies whose ambitions extend far beyond control of Arkham City, while the true forces manipulating the conflict slowly emerge from the shadows.