Set in a future where humans are not the only beings, there are tensions between two races, humans and demihumans known as Ajins. Humans of an age before created these Ajins as slaves to their society. But then a war broke out and the Ajins were freed from their enslavement though still restricted to lead lowly lives.

Kanon Passacaglia is an officer of the East Side Police's Special Bureau's Second Division who are in charge of dealing with crimes related to Ajins. She patrols this city's streets helping all she can.