In 1995, Earth has been conquered by the Zaar Empire from the planet Akron in the star system of Zaar. All Earth's cities have been destroyed, and its survivors live in shanty towns and villages. Kento, a war orphan, and his companions hide in a cave to escape bandits. In the cave they find the secret base of Doctor Earl from the planet Helios, another planet conquered by the Zaar. Doctor Earl had fled to Earth with him the greatest achievement of Helian technology: the super-robot Atlas, whose power increases in combination with the intelligent lion robot Beralios. When the robots combine with the Helian fighter Gumper, they form the mighty robot Daltanious. Doctor Earl entrusts the fight for Earth to Kento, a descendant of the Helian royal family.
The super robot Daltanious was formed from three components: Atlaus (the main robot), Gunper (the spaceship) and Beralios, the mechanical lion who was recovered after the first battle with Akron. The robot is named after D'Artagnan, the hero of The Three Musketeers. Daltanious is 56 metres (184 ft) tall and weighs 678 short tons (615,000 kg). Daltanious was the first combining super-robot with an animal component and the first with a lion's head on its chest. The lion's head would be incorporated into several Brave Series robots, including GaoGaiGar.