The world is dead. A verminous tide of chittering ratmen corrupted the Great Vortex and brought their god, the Great Horned Rat, into the mortal realm. With the thirteenth seat on the Council filled, they set their eyes to the void. Their first conquest was Morrslieb, the Chaos Moon. Made of warpstone, that which they coveted most, they sought to claim it for themselves, to fashion new and terrible machines out of its spoils, to bring Skavendom to never before seen heights.
To this end, they fashioned a weapon of untold power, of a magnitude never before seen, to bring Morrslieb and its warpstone to them. They set to work with a ferocity no other race could match, spurred by a greed no other race could fathom, applying all they had ever learned of the world to this one task. Within months, they had created the world's largest ever rocket, and laid within it the most powerful doomsphere ever to be created. They sent this contraption to Morrslieb, and brought it down upon their very heads. Untold millions died that day, and more in the months after. The entire continent of Lustria was made inhospitable by the falling warpstone, though strangely few traces of the Lizardmen remained. A great winter blanketed the entire world, storms larger than any in history laying waste to everything. But the Underempire endured, as it always had and as it always will, and more than that, it thrived. A great war followed, one that saw all the Skaven's remaining enemies either fall, or bend the knee. When the dust settled, figuratively at least, only the Chaos Dwarfs and Norscans remained, though both were almost entire depopulated. Their defiance had cost them dearly, but in the end they had relented.
The Norscans were largely left alone in the Chaos Wastes, left behind by the rapid advancement of Skaven civilization. The Chaos Dwarfs, however with their technological aptitude and industriousness, and most of all their intelligence, saw the genius of what the Skaven had been able to accomplish. Though grudgingly, for both sides, they accepted a role in the Great Horned Rat's new order. They became scribes and engineers, integrated in part into Clan Skryre's think tank, as it were.
The Old Gods maintained relevance however, albeit in surprising ways. As Skavendom changed, so too did their view of the gods, and thus the gods themselves did change. All worshiped the Great Horned Rat, of course, for he was the true embodiment of the whole of Skaven civilization. That still left niche roles for the Four. The Horned Rat represented the destructiveness of disease and the careless embrace of death, the conniving and backstabbing and shortsightedness that results from unchecked ambition; Nurgle represented disease's transformative properties, and the greater cycle of growth and decay; Tzeentch represented the pursuit of knowledge and the importance of change; Khorne represented the simple acts of war and bloodshed, devoid of deeper meaning or intent; and Slaanesh represented the extremes of emotions not oft felt by Skavenkind. Through the Great Horned Rat, Chaos was truly Undivided.
As for Morrslieb, the sheer amount of warpstone boggled even the Skaven's greedy minds. They swarmed across the carcass of the world, reshaping it in their image. For the first time in history, their cities breached the surface, like festering sores. With the climate increasingly unable to support conventional life, let alone life as numerous as the skaven, they knew something had to change.
The Horned Rat knew that if the Skaven were to survive forever, they would have to spread to all corners of the universe. And so, they set their eyes again to the void, this time to the remaining moon, Mannslieb. There, they found an intact Old One listening post, overseen by an active monitor. It took years for Skaven Engineers to unlock its secrets, but it was so very worth it. The technology and information within catapulted Skavendom ahead hundreds of years. Advanced computing, micro and nano fabrication, and finally the most important piece of all, the Mass Effect.
Author's Note: Well, this is gonna be my first story in a very long time, but I promise to take this one seriously. I've got everything planned out, all I have to do is put words to the page. Gonna try to update this as often as I can, with a mind for maintaining a solid level of quality.
Also, shoutout to my good friend Beastrider9, author of Biomass Effect, who helped me with brainstorming for this story.