The residents of a certain affluent town casually discard objects. However, this waste is invaluable to Rudo, a dweller in the town's slums. Despite constant warnings from his adoptive father, Regto, Rudo spends his days hunting for reusable materials that would otherwise be sent to the massive disposal zone known as the Pit. Because of its sheer scale, the Pit also serves as a method of criminal punishment; anyone dropped in is never to return. When Regto is murdered by a mysterious attacker, Rudo is wrongly accused of the crime and thrown into the Pit. To his surprise, he wakes up in a junk-filled area inhabited by colossal monsters formed from trash. As the toxic air and Trash Beasts push Rudo to the brink of death, he is rescued by Enjin, one of the Cleaners who wield weapons called Vital Instruments to battle the monstrosities. After acquiring his own Vital Instrument, Rudo soon joins the Cleaners, hoping to find a way to escape the Pit and avenge his father.