No one remembers what being dead used to be like.
Maybe a stoic old god once presided over the souls of the restful dead in a great hall.
Maybe there was simply nothing, and no one to experience it.
The only thing that is certain is that most theories are far better than the current reality.
When a living thing dies, its soul–or shade, or copy, or some other facet of its being–is taken somewhere else. That somewhere else is a never-ending prison of pain, misery, and psychological torment, at least when things are operating smoothly. This underworld for lack of a better name is presided over by a seemingly infinite assortment of malicious entities whose greatest–but not sole–calling is mortal suffering.
If a new arrival is scooped up into their shadowy yet too-real clutches, they quickly learn that all the awfulness of life was just a prelude to this. Pains new and familiar are visited upon them ad nauseum until they become numbed to them. The torturers switch their cruelties up regularly, many specializing in different forms of pain. This continues until the very fabric of the shade's being unravels, and they cease to be. This unraveling is only a temporary reprieve, however. Soon the shade coalesces together again, fresh and ready for new agonies.
This is not a punishment for anything. This underworld is not a place where transgressions are paid for. Everything–saintly, sinful, and standard–comes here to suffer. It is suffering for its own sake, and the shade is nothing more than a conduit through which suffering may flow.
This only happens if the shade is captured, of course.
The underworld is a vast, ever-changing place, with many nooks and crannies in which to hide. All of it is hostile and unwelcoming, but not all of it is beyond the means of the dead to resist and overcome- especially when they work together.
At some point in the murky past, a resistance movement of sorts formed. United by common cause and a general aversion of infinite torture, mortal shades started to band together on the desolate fringes of the underworld, scraping an existence out of the rocks and launching guerrilla raids on their jailers, whom they have given many names to in an attempt to better understand and confront with them. Every soul they find, whether newly died or wrested from the clutches of the torturers, is another particle of spit in the eye of the underworld.
Being a Shade
Your body, if it can be called that, looks like an unusually dense cloud of shadows and dust in its natural state. It is highly mutable and morphic. Your torturers use this to their advantage when they have you at their (lack of) mercy- most of the deformed, tortured-looking edifices and objects you find dotting the underworld were once (or rather, still are) other shades.
But you can also exert control over yourself. This provides a number of unexpected benefits. You may appear in any way that you please, and you may change that as often as you wish. You may look as you did in life, or as you always wished you had looked, or as whatever essential 'true' self you think you have, or something entirely different- age, species, gender, and all other permutations of being have little bearing down here.
You may even take the form of an inanimate object, in case your friend needs a weapon in a pinch, or you simply always wanted to be a fancy bauble.
Other shades will always be able to perceive you as 'you', just as you can recognize them. Call it a familiar aura, if you want.
You sense and perceive things in the manner that you are used to, albeit in ways that are either dulled and muted, or too painfully acute. You don't need to eat, drink, or sleep, but you still suffer from hunger, thirst, and fatigue. You can shrug off a remarkable amount of damage, but the pain lingers for ages.
Even without infernal tormentors, existence down here is an endless, inconvenient chore.
Just like home, right?
On the topic of your new home, there is much to say- infinitely much, in fact. Shades before you have tried, but none have ever found the full extent of the underworld, nor have they been able to extract information on the subject from captured demons. You will probably be no different.
But your kind are not wholly ignorant of this new, unwelcoming world that you find yourselves in.
Some things are tried and true.
The underworld seems laterally infinite, but only occupies a vertical space a little larger than its largest mountain chains. Admittedly that is not saying much because even the smallest of the underworld's hooked peaks is several times larger than anything you ever saw in life. But there is a top, and it's rumored that shades have even seen what occupies the vaulted ceiling, high above the roiling neon clouds.
Apparently the revelation was worse than a thousand simultaneous unravelings, and their screams are still carried on the acrid wind to this day.
The underworld is constantly changing to make itself more hostile to anything passing through it. Within a matter of hours a small, dry cave entrance used as shelter can warp into the dead center of an enormous, thorny labyrinth.
Two things can temporarily fix a point; observation, and anguish.
By being present and cognizant in an area, you and other shades can slow or halt the landscape's changing. In this way, you can carve out and maintain territory long enough for it to feel familiar. This is how cells of free shades tend to operate. You cannot shape the land as you wish- that is a privilege enjoyed only by very powerful or very numerous evil spirits.
Pain also fixes a point in space. The biggest and most hideous bastions of your tormentors have stood unchanging for eons, maintained by the incalculable suffering that goes on within.
You will probably be driven out of any area before you can call it home. Fortunately, you probably don't have a lot you have to carry around with you.
Death, it turns out, is not a perfect equalizer. Sure, you're all shadows and dust flung into the maw of evil, but some start off better equipped than others.
You begin play with a small assortment of items copied from the objects surrounding you at the time of death and/or burial. This may include the clothes and tools you were buried with, food that was burned with you, or even a living thing that was sacrificed to honor you- generally an animal like a horse or domestic cat. Or perhaps you were sacrificed in honor of someone else, who was quickly carried away by demons, leaving you to carry away their grave goods.
You can only bring as many facsimiles as you can carry on your person, or else coax along with you. If you were buried with all of your material wealth, it turns out you really can't take it with you. Fortunately, money is worthless down here unless it's forged from another tortured soul.
Echoes of Before
You may remember your entire life, fragmentary pieces, or nothing at all. Each brings you great pain and regret. But it can also bring you strength.
Despite lacking muscles, you have a kind of psychic muscle memory of your past skills and abilities. You may have had great strength of arm, quick wit and skill, arcane power, or some other cliché categorization of capabilities. If you somehow survive the cruelties of the underworld without unraveling and losing almost all of yourself, you might be able to plumb the depths of your past a little deeper, and tease out more of that ability dormant deep within your anguished psyche. Or, you can forsake the past, and follow a new past entirely. Thus may you specialize, or branch out.
Take heart and choose as you will. There are no right or wrong answers. Only slower or faster routes to failure.
And when you do fail, it will hurt. Whether you are defeated in battle, or ensorcelled, or betrayed, you will eventually wind up in the clutches of your tormentors. With luck, your comrades in arms may break you out of whatever hellish holdfast you've been hidden in before it's too late.
Luck is rare. Most likely, you'll unravel at least once in your time away.
When you do, you lose bits of yourself. First your most recently acquired skill go, followed by, memories, and finally the fundaments of your being. Eventually all that will be left is your capacity to register and feel pain.
But each time you unravel, you slip your bonds by dint of vanishing into whimpers and smoke. You'll reappear somewhere close by, but not so close that you won't have a head start running away from your captors before they catch you again. Until next time.
Demons, evil spirits, torturers, "the neighbors"; all are popular terms that refer to your enemy. Your foe is infinite in shape, number, and depth of sadism, and seemingly unstoppable in the long term. Every loathsome monster you can imagine and many more that you cannot has its place in these hellish ranks.
Still, they are not invulnerable. They are made of the same wispy stuff that you are, and can thus be disrupted and even 'killed'. Unlike a shade who unravels for a time, most slain demons rejoin with the underworld itself, their essence recycled into some new nightmare, sometimes with lingering memories and abilities, sometimes without. Don't dwell overlong on the implications this has for you shades.
They start off simple-minded and weak, but quickly develop skill, cunning, and individual personality as they express themselves through the suffering of shades. They know how to communicate with you, and will do so mostly to mock or deceive you. They seem to have their own ranks and hierarchies, but who or what is at the top is a mystery.
Far more immediate a threat than some unknown dark lord is the demon you know all too well. Perhaps it was your first torturer, or your first 'kill'. Maybe you barely eluded it, enticing it to start the chase. This creature is your Nemesis. You are as free to decide what it looks like as you are to shape your own shade, because it always embodies what you personally find most awful and revolting.
It has no unique power save for its unnerving, intimate familiarity with you. It cannot sense you by some supernatural means, yet it will always find you, sooner or later. It is like a second shadow, always trying to latch onto you. But this familiarity goes both ways. Over time your fear and hate for it will crystallize into wisdom, and the power to exploit its weaknesses.
It would like nothing more than to break you. Break it back.
There is no escaping the underworld- dead is dead. Likewise, you can never defeat your tormentors.
But you can spite them. You can deny them their sadistic purpose and evade capture indefinitely. Alongside your fellow shades, you can create a community and carve out a 'living' for lack of a better word. You can even dare to feel more positive emotions.
There is a legend--probably made up by demons just to give your kind false hope--that one form of escape is possible.
By breaking all fetters and facing one's nemesis with all fear, misery, and even malice scoured from their soul, a shade might collide with it in a manner not unlike matter meeting antimatter. Complete, mutual annihilation ensues. This grants the shade sweet, restful oblivion, but it also forever deprives the underworld of one of its jailers.
A meaningless feat on its own in the face of infinity, but with enough repetition over time...
Possible Origins of the Underworld
The other gods, jealous of the size of the kingdom of the dead, usurped the god of the dead. Your agony is a reagent in the spell used to keep it imprisoned.
Suffering is the fuel for all existence. If the underworld stopped its hellish work, the universe would collapse.
God was pandeistic, and the underworld is a particularly large, rotten piece of its corpse. Tormentors are its maggots.
Some cosmic force is desperately searching for someone special. Only an eon of unraveling will reveal the chosen one.
This is all the nightmare of some fitfully slumbering god.
The underworld is alien in origin. Its creators use it to experiment and collect data on you.
With enough torture, every shade becomes a demon. The denizens of the underworld need you in order to reproduce.
Somewhere deep in the underworld, tortured souls are being forged into an impossibly huge machine of unknown purpose.
This really is a place of punishment. Your unforgivable sin was existing.
This is the real world. You were just dreaming before.