The human world and the demon world (yōkai) have overlapped, with humans going about their daily lives while demons walk the same streets unseen by ordinary eyes. For a long time, a young-looking woman named Yurine and her servant, the Karas (meaning "crow" in Japanese), have maintained order and balance between these two worlds, preventing demons from interfering with human lives. However, humans have forgotten and mocked the existence of demons, no longer appreciating the privilege of living without fear. Disgusted by this arrogance, a former Karas turns against the laws he once upheld. In his human form, named Eko, he assembles an army of Mikura—mechanized demons—to prepare an assault on humanity.
A young man named Otoha inherits the power of the Karas and takes his place beside Yurine, who claims that his soul called out to her while he still lived as a human. They dwell in the demon world. Now Otoha must prove himself as a Karas and restore the balance that Eko threatens to shatter.
Meanwhile, a superstitious police officer named Sagisaka and his rational new recruit, Kure, follow the trail of murders committed by Eko's Mikura, as well as the path of a rogue Mikura named Nue. From this point, the prophecy unfolds into a grave revelation for everyone in the city.