Titanic agglomerations of hypertechnological growth styled in the designs of human architecture. They can be vast and expansive or cramped warrens of tunnels and chambers, but always they are impersonal, inhuman replications of sane design, the N-matter suffusing them granting the ability to surpass any human construction in size and complexity.
Upon the crust of these monstrosities is where most of human civilization can be found, caught between the broken void of outer space and the transhuman ecosystem of the depths. Upon mounds of shattered stone, dunes of dust, layers of plastcrete expanse, and the rare refuge of organic detritus, the people of this era burrow into the hide of the structures, siphoning power, carving out homes, and raising fortresses to protect themselves. Irrational patterns are ordered into habitability and tamed to serve the ends of its denizens.
But this mastery is tenuous. The environment is hostile, its inhabitants lethal. The ecosystem is adapted for civilization; human cities are no longer a displacement of the natural order, but a part of it, one which is accounted for by its predators and parasites. While ingenuity and metacognition allow humans to retain an edge against their natural enemies, it is always threatened by organisms who can surpass that through the complexity of their instinctual combat routines and innate weaponry on par with any tool created by civilization. The megastructural ecology can be defined as a long, slow war of all against all, with thinking beings just one part of an immense food web. While they are far from the bottom, they are no longer at the top, either.
A miraculous post-singularity substance which has reshaped humanity and the star system. Developed by chance at its edge during the decaying paradise of the Solar Empire, its nature as a self-replicating, highly intelligent substance caused it to take root in humans and use their own mutability as a crucible for its evolution. Humans integrated with N-matter could integrate machinery into their bodies, accept new organs with ease, and push the boundaries of what the laws of science at the time allowed. Unable to be suppressed or monopolized, it has slowly overtaken all forms of technology, and now pan-humanity is dependent on it to survive in the ruin it has created of a once-rational universe
Despite how ubiquitous it has come to be, little is known of its inner workings. It is wielded blindly by its users, who intuitively create impossible technologies as naturally as they walk and breathe. But once something is produced, it can be replicated. Invented by posthuman intelligence, these devices are then passed on to mundane sophonts and percolate through pan-humanity, allowing for the development and spread of N-matter-based civilization.
Unable to be produced from nothing, it is instead grown, cultures of N-matter feeding on the richest and purest materials harvested from the megastructures. High-end computronium, energy-dense storage devices, and the strongest alloys available, all are required to allow for its reproduction. Others, however, harvested it in trace amounts from the megastructures themselves, carving immense wounds into their bodies and grinding up their architectural flesh for the motes of godhood saturating it. And still others turn on one another, preying on thinking beings to harvest the N-matter accumulated in their own bodies, for the substance seems to have a preference, if it can be called that, for co-opting the bodies of living beings and further augmenting their complexity.
While countless vital resources exist, none are so coveted as the N-matter from which they stem. Its assimilation into the body spurs impossible evolution, allowing any being to transcend their form and obtain immense power. Even the most desperate and impoverished soul can rise to the top of society if they manage to obtain an N-matter core, and any society of note is assuredly ruled by such individuals.
This potential is not without cost. The widely-spread and unpredictable saturation of N-matter means that anomalous individuals and monsters can appear anywhere, at any time. The balance of power is constantly disrupted by extraordinary existences challenging the status quo. Sometimes they are rebels seeking to overthrow an unjust system, other times monsters seeking to usurp it. Some simply kill for the sake of killing, or to augment their own power by feeding on their kin. Others leave, fearful of the reprisal their rebirth will bring upon themselves and their loved ones.
As empowering as N-matter is, the chaos it produces has led to a world where peace is a dream and stability an illusion. There is only a chaotic pyramid of shifting relationships, tenuous alliances, conspiracy, and disaster.
But to those who can navigate these challenges, who can avoid the descent into monstrous ego death, the world is theirs to shape as they see fit.
Until they meet something stronger than themselves, anyway.
We dwell in a smothered cradle. The stars are dim, blocked out by the immense clouds of dust and particulates ejected by the hypertechnological processes of the long dead god-beings which ushered in the final night. Our twinkling lights are the witless colonial growths of the megastructures as they consume and reshape all matter within the system. Immense space elevators, orbital rings, habitats grown out like architectural teratoma; these all drift through the black. Every asteroid burrowed into, hollowed out. Every moon scraped clean. Space is no longer empty. It is crowded with ruins.
What dwells here is dead, dying, or barely clinging to life. Living there is to do so as a lone scavenger in a sea of airless dark, or in a tightly compacted autocracy, where water, food, and air are endlessly recycled; the distributor-masters having the power to shut it off at will.
But these islands of survivors are rare. There are things in the void that are immense, hungry, and inhumanly intelligent, drawn to these islands as maneaters are to the light of a fire. The greater celestial spheres are always safer. Pulled down as if by gravity, much of humanity has fallen back to these planetary bodies, the locations of the densest megastructural growths and their power and resources, along with a natively breathable atmosphere.
These cold estuaries, lit by the dull white of a choked sun, incubate and shelter civilizations from entities which would prey on them, granting them time to develop and produce monsters of their own. While some grow strong enough to contest the void and even claim a portion of it, they never last. There are always more monsters in the dark than there are lights to drive them back.
There was once a network that connected every settlement in the star system. Updated by relay nodes, maintained by tireless labor, and spread throughout all human civilization. At once point, it was seen as a necessity, as sure food, water, or air. It connected cultures across unfathomable distances, and allowed for control and regulation undreamt of by earlier generations.
Near the end of its life, and its apex, people even sought immortality through it, uploading their minds to its storage centers to live as virtual beings, free from the confines of physicality and baseline perception of time. It was even thought that one day such entities would outnumber all humans alive in the real world.
It is dead now. Swallowed up by a digital jungle of hungry malware, ceaselessly expanding into all storage space it can find, its denizens ceaselessly gnawing on each other to carve more space for themselves.
The product of exponentially complex info-warfare being dumped into the network, along with the expansion of the megastructures and their gradual distortion from places where humans were meant to live into independent ecosystems, saw the datasphere deteriorate into its present state.
The vast expanse of digital space within the star system is the hunting ground of virtual intelligences which prey on one another to obtain their storage space or siphon data to become more efficient at doing so. They choke the life out of one another by flooding them with junk data or fragment them into oblivion with viruses that destroy critical programs. And a human mind is just as valuable a storage system as a server rack. Those who enter the datasphere without protection risk having their minds burnt out, or worse, their personalities overwritten by a malignant mind, now released into the physical world.
What safe places exist are isolated, airgapped local networks, any entrances to the datasphere proper guarded by powerful AIs or uploaded consciousnesses worshipped as deities by ignorant locals, and treated with like one even by those who know better. Half-senile, unfathomably powerful, and largely self-interested, they can be handled no other way.
While individuals can be careful, or even just powerful enough to not require their services, the average denizen of the current era is reliant on them to live comfortably. Otherwise even a single lapse, a careless slip while browsing digital space, can lead to the ruin of cities. It is no surprise that the nomads and hermits of the megastructure are paranoid and supersitious to the extreme.
They cannot afford not to be.