Daigo Ōtaki begins as a reckless teenager navigating a desolate landscape on his super cycle, accompanied only by a robotic black panther companion. He arrives at the artificial Victor Town just as fanatical invaders with advanced weaponry attack. Compelled to join the town's defense force, Daigo fights back against overwhelming odds.

Later revealed as an orphan raised by his uncle, Daigo learns upon adulthood that Victor City was originally planned by his late father, a genius scientist. His sister, Saori Ōtaki, manages the city and informs him of his inheritance: the sophisticated Gordian super robot system. This legacy comprises three progressively larger robotic containers: the human-sized Protteser (Protessa), the intermediate Delinger (Deringer), and the largest Garbin (Gadeen), standing 15 meters tall.

Accepting his inheritance, Daigo joins the Mechacon mechanic combat 18th regiment unit, Victor City's dedicated law enforcement defenders. He pilots the Gordian robots to combat the antagonistic Madokuta organization responsible for the attacks. Daigo strategically escalates his deployment from Protteser to Delinger and finally to Garbin to counter greater threats.

His journey centers on unraveling the mysteries of his identity, Gordian's origins, the invaders' motives, and the truth behind his father's work. This involves confronting the Madokuta organization in numerous battles to protect Victor City and its inhabitants.