Japanese thriller. A bloodthirsty killer who has been living in the woods is drawn to the banks of a raging river by a voice inside his head. He is pulled in by unseen forces and washes up in a small mill town adjoining a pig farm. There, he meets his female alter ego (and the source of the siren voice) working at the mill. She shares his bloodlust and together, they invoke the aptly named 'human hog monster', a frightful manifestation of evil that wreaks havoc upon the unsuspecting villagers.