From introduction:
The ancient city of Zyvoth lies unpeopled, wreathed in darkness, just waiting to be plundered. But who would dare such a quest? Astral wizards and their foolhardy minions, perhaps. Or those who gambled with demons and now must pay their debts, no matter how extravagant. But even though the Zyvothi have vanished, ascending to some higher plane of infinite brilliance, the city has never been lifeless.
The old guardians remain. The constructs the Zyvothi left behind continue to patrol their domains. Eight-sided diamonds fly over the city skyline, lashing all intruders with their psychic whips. But what is an “intruder” in this day and age? There are creatures in this city they see as merely animals and ignore. Would those creatures feel the same? Would the Zyvothi? It matters little, for it does not change how these mechanisms conduct their duties.
One creature that has free reign over the abandoned city is the sableworm. Enormous tubes of jet and bioantiluminescence, they are the tyrants of the streets, pushing other invaders out and claiming turf for themselves. But they are not builders. They have no skill in architecture, engineering, or repair. The city falls to ruins around them. Tangible darkness leaks from the darklight generators into the streets like a suffocating fluid.
New ecosystems develop, and other creatures rush to occupy them. Darkfish swim through this inky, fluid darkness that pours like a sludge through alleys and basements. Evolving faster than the other creatures of this realm, they are claiming ground that others would drown inside of.