Part of a Fire Emblem story I might be working on:
To say Fhirdiad is cold is to say “A star is warm” or “The Archbishop is religious.” Thousands of years before the foundation of the First Adrestian Empire, during the Great Seeding that spread humanity across the stars, a fleet of colony ships came to a lush and verdant world with one purpose: to establish a new home. While much knowledge of this ancient mission has been lost or devolved into legend, what is known is that the so-called Northland Expedition left Old Earth for a planet in what has since become the Faerghus Veil.
For the first five hundred years, the colonists of a world named for an ancient Earth-king, thought they had landed in a perfect planet - apparently so young that the only complex lifeforms on land were simple plants and animals, but old enough that its atmosphere would be perfect in many ways for the plants the Northland Expedition brought with them. They established a thriving colony, which itself established successful settlements across the planet. Terraforming proved effective quickly, as Earth plants and animals took root and spread across the planet in record time. The few naysayers were laughed off and pointedly ignored, their warnings of cyclical extinctions and soil layers ignored as “something for later generations.”
Then the frosts came.
Daman, Fhirdiad’s largest moon, was observed as having a very wide, very slow orbit - since the time it was first seen from long-range telescopes on Earth, it had barely moved in the centuries that the colonists had spent sailing through the veil. What they did not know of was the asteroid that would smash into its dark side and push its orbit closer to Fhirdiad’s surface - and as it came closer, the effects of its sudden proximity were felt very quickly.
The coastal settlements were quickly swallowed up by massive tidal waves. Magma was forced by gravity through well-worn channels, erupting in vast calderas across the planet’s surface, belching vast clouds of ash and dust into the sky. At its closest point, satellites once orbiting Daman were pulled from the moon’s grasp and rained down across Fhirdiad itself, only adding to the global volcanic winter. To make matters worse, chemical reactions from the impacts and the volcanoes released colossal amounts of methane into the atmosphere, making the air nearly unbreathable and obscuring even more of the star Daire’s warmth.
Trapped on the planet, and having dismantled their ships, the helpless colonists could only watch as their carefully-built ecosystem began to die. Great advancing walls of ice crept southward, chasing Fhirdiadites towards the equator as the oceans began to freeze. Millions were abandoned to die who could not move fast enough, as the last autumn rapidly became an endless, unbroken winter.
Trapped on a thin strip of relative warmth, the desperate survivors of an icy apocalypse huddled together, succumbing to despair and starvation. It is not known what prompted the iron drive to survival, but it is known that the ancestors to the Elite Blaiddyd came to lead the effort. Pursued by the icy grip of death, the denizens of Fhirdiad began to dig. They built vast underground cities in rings around the massive caldera volcanoes that had killed their world, using them for warmth and geothermal energy.
Iron discipline, autocracy, and pragmatism ruled these survivors for hundreds and then thousands of years. Unlike Derdriu, Garreg Mach, or Enbarr, the three other great city-worlds of the Fódlan Sector, Fhirdiad was united under a strong central authority very early in its history. The great underground citadel of Lionsgate, ringing the caldera known as the Lion’s Maw, offered its devotion to a single strong High King, and the other cities, radiating out from this subterranean metropolis, bent the knee to it in turn. Unlike the Leicester Confederacy, with its devotion (or, well, lip service) to the ideals of democracy, or the Adrestian Empire’s bureaucratic parliamentarianism, the progenitors to the Holy Kingdom of Faerghus only knew a single, strong ruler for millennia.
For thousands of years, Fhirdiad’s people worked to stay ahead of the snow and ice. The lowest levels of the oldest cities are miles below the ice by now, with only the highest spires poking through the glaciers to scrape the iron-gray sky. Like this the icy world stayed, until the arrival of the first explorer-ships from Garreg Mach. They shared the technology of the jumpgates, allowing the Fhirdiadites were finally able to flee their hellish world - and flee many of them did, founding colonies across the Faerghus Veil. Arianrhod, Tailtean, Teuates, Rhodos - dozens of worlds were claimed in the name of the High King of Fhirdiad - later the High King of the Veil. Supplies from these new colonies led to the explosion of the population across the planet’s surface and under it, with the Lionsgate expanding to a truly unbroken city across the planet’ surface, powered by the sheer energy of the world’s hyperactive mantle.
Today, Fhirdiad is the throneworld of the Holy Kingdom of Faerghus and the ancient Blaiddyd line. Ninety percent of the planet’s seven trillion people live underground, with a clear social hierarchy based on one’s proximity to the surface. It is a squalid place the farther down you go, with those on the lower levels seeing no other sky than alloy and piping. A plague, suspected to be bioengineered by enemies unknown, recently swept through the lower levels, leading to an swell of unrest - the largest in centuries - that was only stopped when an influential psionic, Cornelia von Arnim, led a massive humanitarian effort to stop the virus. With King Lambert killed in the Duscur Incident, and young Prince Dimitri not yet of an age to take the Winter Throne, the power vacuum has only thrown this troubled world into yet more chaos. But the Fhirdiadites have conquered the Frost itself, and this should be no problem for them to get through.
...Right?