Set in a distant future, Heroic Age tells the story of the quest of the human race to find the messianic individual that holds the power to save mankind. This savior, named Age, is the only human to have been raised by the Golden Tribe before they departed from the universe. The young princess of the humans, Dhianeila, and the crew of the Argonaut - an advanced spaceship able to travel between stars via lanes called Starways - find Age on the ruined planet Oron. After fending off an attack from a rival tribe, the Bronze Tribe, the human race sets off on a journey of salvation, led by Dhianeila and Age.
There was once a primeval race which called itself the "Golden Tribe". They possessed many powers, including the ability to create Planets and see into the future. They then called on primitive beings far across the galaxy and told them to explore the universe. Three races were able to reply to their call and the Golden Tribe referred to those as the "Silver Tribe" (銀の種族 Gin no Shuzoku) , the "Bronze Tribe" (青銅の種族 Seidou no Shuzoku) , and the "Heroic Tribe" (英雄の種族 Eiyuu no Shuzoku) . Long after, just as the Golden Race was about to move on to another universe, a new race replied to their call. The newcomer, Humankind, was referred to as the "Iron Tribe" (鉄の種族 Tetsu no Shuzoku) .
Due to their extraordinary powers and aggressive nature, the titanic beings known as the "Heroic Tribe" instigated an interstellar civil war and caused the destruction of thousands of planets and stars. The expanding ruin angered the Golden Tribe, and forced them to capture and punish the surviving five members of the Heroic Tribe for the destruction they had caused. Caught in a magical cage, they were subdued and condemned to serve races weaker than them. Reduced to the state of diamond-like stones, they were given to five individuals, who were then referred to as 'Nodos' (ノドス Nodosu) . The Heroic Tribe member, Bellcross, entered the body of a boy from the Iron Tribe, and became known as the fifth Nodos. The child was directly raised by the Golden Race on the ruined planet, Oron, in order to fulfill a prophecy passed down by the Iron Tribe's royal family.
It was then that the Golden Tribe issued prophecies to each Tribe (Iron and Silver) who possessed a Nodos, telling them that they could make contracts with those exceptional beings and allowed both parties to draw a specific number of clauses, called 'Labors'. In the Iron Tribe's case, there are twelve conditions, the famous 'Twelve Labors', assigned to a yet to be found, lone human announced as their new messiah: a teenager named Age.
However, soon after they came into play in the equation, the Iron Tribe's homeworld, Earth, was attacked by several dozen hives from the Bronze Tribe. The local population was exterminated and the planet conquered, forcing the survivors to emigrate towards safer parts of the universe. It was later revealed that the attack had been staged by the Silver Race, who ruled over the insect-like Bronze Tribe. To this day, the Iron Tribe is still greatly endangered by the combined forces of the Silver and Bronze Tribes and, although its new homeworld is still ensconced in a relative sense of safety and secrecy, its survival, however, is only guaranteed by this stealthiness, as the difference of power between the youngest race and the others is still too great.