Residing in the slums of a prosperous town, Rudo and his foster father Regto attempt to coexist with the rest of the town's residents, though Rudo harbors a deep disdain for the upper class's wastefulness. Disregarding warnings from those around him, Rudo habitually sifts through the town's garbage, searching for anything useful or valuable to rescue from the "Abyss"—a colossal pit where all items deemed trash are discarded, including people. Rudo's biological father was one such victim, having been cast into the Abyss after being accused of murder. One day, after encountering a mysterious figure on his way home, Rudo returns to discover Regto's dying body on the floor. He is promptly apprehended by the authorities at the scene and charged with murder. With no one believing his claims of innocence, he is thrown into the Abyss. Rather than perishing, however, he finds himself in a strange, foul-smelling location surrounded by monsters composed of trash. When Rudo is attacked by these monsters, he is rescued by a man named Enjin, who reveals himself to be a "Cleaner"—an individual who employs special weapons known as Vital Instruments to battle these creatures. To exact revenge on the person who killed Regto, Rudo reluctantly becomes a Cleaner, fighting his way back up and out of the Abyss.