Goblin King Deros rules the Goblin Society, a subterranean race sealed beneath the Earth by ancient forces, potentially connected to Greek mythology or other early pantheons, for over 10,000 years. Driven by the imminent extinction facing his people if they remain underground within a year, he relentlessly pursues the legendary treasure Quaschika. This desperate timeline fuels his ruthless actions.

Deros commands through a strict hierarchy, relying on his priest Gepeu and four specialized generals: Cera (White), Agyle (Red), Groizy (Black), and Bluzon (Blue). His leadership enforces absolute authority and merciless punishment, executing failed subordinates and employing torture. Despite this brutality towards enemies and underlings, he possesses a genuine, albeit twisted, dedication to his species' survival, viewing their return to the surface as a righteous reclaiming.

Deros exhibits no personal evolution or redemption. His singular obsession with Quaschika remains constant, driving increasingly destructive campaigns against the Rando family. The finale reveals Quaschika as a cosmic reset mechanism designed to purge irredeemably corrupt civilizations. Deros fails to secure it, and the protagonist Tatsuya Rando activates the mechanism. This results in the near-total annihilation of Earth's inhabitants, including the Goblin Society. Deros perishes; only the Rando family and one Goblin general survive to repopulate a new universe.

His background lacks explicit elaboration, though contextual clues suggest the goblin banishment may relate to conflicts with pre-human civilizations or deities. Deros operates from a desolate temple bearing resemblance to Atlantean architecture, hinting at possible ties to that lost culture. No spin-offs, films, or OVAs expand on his origins or depict alternative outcomes.