The people of Earth go about their daily lives, without a clue that another world lies deep beneath their feet. Numerous subterranean nations who have never seen the sky. The most powerful and feared of all these is Subtopia.
It’s people bear an exact resemblance to humans. But their bodies are able to absorb and store Earth’s magnetic energy. endowing them with super strength, flight, invulnerability, healing, longevity, super vision and hearing.
Subtopian society is not unlike ancient Rome. A harsh, warlike civilization of ruthless imperialists. For generations they have been expanding the borders of their empire by conquering other underground nations. Those who are not slaughtered in the initial assault live out their days as Subtopian slaves, forced to wear explosive collars their masters can detonate at the slightest hint of disobedience.
They consider themselves superior to all.
The 1st born of each family is required by law and tradition to join the warrior class. The 2nd born is made an explorer, to seek out new lands for the warriors to conquer and activate a war-beacon, sending a route back to Subtopia so they can begin the invasion.
The holy grail for the explorers is the Surface World, believed by many to be only a legend. Most explores are sent in search of it only to die in the shifting plates.
One of their most sacred rites is the Blood Duel of Chalatar. In which a younger member of a house fights another to the death to take their rank in the house. Once a challenge is spoken it cannot be taken back and must end in death.
In the early 20th century the Subtopian explorer, Rex of House Titanium, became the first to reach the surface world. But broke his oath to protect them. A century later his brother Dax found him and began the invasion of the Surface. Which was only just repelled by Rex and a rag-tag resistance.
But the Subtopians are still down there and it is unlikely they will let this defeat go unavenged.