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

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