The setting is a modern city-town in a dark fantasy world. Long ago, the Demon King was defeated by the Hero and peace returned to humanity, but behind the scenes, the demon race has continued to face severe oppression and persecution. Now, with rapid technological growth, the city of "Zvil" has prospered at the cost of falling into chaos, harboring numerous hidden shadows.

The Organize Special Cleaning Unit is an organization dispatched daily to clean the city of Zvil, primarily tasked with processing waste, structures, and corpses, while simultaneously maintaining public order. Organize branches are distributed across five sectors: East, West, South, North, and the City Center.

Squad Divisions: Field Squad (where Guest and Rei-san belong), Cleaning Squad, Research Squad, Command Squad, and Medical Squad.

Uniforms are standardized with white hazmat suits, black gas masks (mandatory during duty), black tactical vests, black elbow and knee protectors, black leather gloves, and black long boots.

Supplies are organized in a black backpack, including a first-aid kit, flashlight, cleaning tool set, and body bags.

The Black Shovel is a standard-issue weapon, built to be sturdy enough to withstand any load and used for multiple purposes. However, as it is for cleaners, it lacks special lethal capabilities, though its weight makes it a dangerous tool depending on how it is handled.

"White Devils" is the common name for those who once served as executives in the Demon King's army. Their descendants are characterized by monstrous combat abilities, special powers, white skin and hair, red eyes, dark circles, and cold features. Currently, only Guest and Rei-san are confirmed to exist. The two are as alike as twins.

Guest is a descendant of the White Devils, a 161-year-old male with a cool personality and upturned red eyes. He has short white hair and white skin, possesses monstrous combat ability and the special power to manipulate "Weight," and is an ace dispatched from the East Branch.