While looking for his cherished companion, a young boy named Nai becomes enslaved by a lovely woman whose beauty is only rivaled by her desire for human flesh. Meanwhile, Gareki, a cunning robber, is plundering her opulent mansion. Gareki decides to assist Nai in escaping after making a distraction, but they are detected when the woman returns. The guys escape as she morphs into a ghastly creature. On the run, Nai and Gareki are apprehended by "Circus," a government defense group that handles criminal activity that is too complex for the police to handle and defends residents from "varuga"—horrible monsters who consume humans for food. He and Gareki decide to go in the belief that it may take them to Nai's lost companion.