Deities of Erra wish only the best for humanity. They always did. They always do. They always will.
humanity didn't understand this at first: the deities of Erra look
like grotesque children of Bosch and Dali, put through a shredder and
assembled at least partially in some different dimension. Too many eyes,
mouths, arms, glittering surfaces, rotting tendrils and truly odd
angles for everybody's comfort. Just looking at them causes all kinds of
migraines, like a condensed week of disco. Even after humanity got
somewhat used to their appearance (habitually portraying them as
beautiful humanoids or abstract symbols) their true visage is not for
the weak of heart.
Of course, if you go mad or die from a cardiac
arrest they will gladly resurrect you to full health, while apologising with awkward profoundness. Despite their troubling appearance, the deities of Erra are the
nicest, most benevolent deities you can meet in a multiverse, any multiverse. They always
wish you the best. They will answer your prayers as best as they can,
asking for nothing in return, attaching no strings, making no delays,
expecting no sacrifices, no code of conduct, no loyalty, no worship. They believe
only in the very best of humanity, and are so exceptionally, so profoundly naive in this belief that you can make up even the slimmest
justification for why you need to kill a bunch of people and they'd provide the means.
do not portion their powers, they do not take away the powers, they
don't gate their powers by any kind of criteria short of open
destruction of world and/or species and such other Not Nice stuff. It is still possible to do, you just need to be creative.
They answer all prayers all the time. All the prayers, of everybody who is able to formulate even the simplest one.
This made the humanity of that world a bit weird.
It doesn't really matter what world it was before. If it didn't have gods, now it had them. If it did have gods of kind that didn't actually exist, how they were delegated to abstract philosophy instead of being objects of worship. If it did have gods, they were of the kind that grants carefully measured powers to selected few individuals, and couldn't withstand the competition which provided all of powers to everybody all the time. If the world had arcane powers then mages, those selected few who trained to wield them, were very quickly outnumbered and their god-sorcerer empires fell. Arcane is still here but it is just a hobby for their wielders, because deities can emulate many arcane wonders up to a certain degree.
When the deities first appeared on Erra, people were quite perturbed. Spontaneous healing,
dying and resurrection were a bit mind-shattering, and
that wasn't even all that was happening. It took humanity about a generations to fully figure it all out, but this generation grew up in
somewhat apocalyptic world with all social structures failing. Nobody was hungry and defenceless anymore, no tyrant could hold their slaves in the slavery anymore. Everybody had visions of very disturbing creatures waving their appendages on them but suddenly everybody was also tossing miracles around, As long as you had at least one friend who could say a prayer for you, you couldn't die, so murder became trivial and with this, the many of moral and ethical codes.
There were attempts of those in power to hide this new state of the world from their herds. But the prayer is a very basic thing, and it didn't even need to be any kind of formal reciting that could have been banned - just make a wish in your mind quietly.
Eventually humanity invented new ways to kill, but it took some time. In meanwhile, the newly made inquisitions from churches that went all fire and brimstone, weren't doing any progress and made more of fools out of themselves.
through trial, error and some direct divinations humanity figured it out that deities
aren't evil abominations despite their looks, that deities grant
miraculous powers to anybody and ask nothing in return, and that deities are very-very much like that
exceptionally dumb and exceptionally friendly kid with unlimited bank
account you can persuade to buy you a Ferrari and then the whole Italy just for a pat on a
Deities are very
powerful but also limited in scope of what and how they can give. Sure,
they can bring thunderstorms, raise dead, create diamonds and transport
things around the world in a blink of an eye, but they do not understand human nuances at
all. Take this one example as a highlight: the blue gooey paste that deities send as a
food wholesomely provides all needed nutrients and satisfies hunger but even centuries
later still tastes like liquorice and still is blue, despite great many prayers to change this.
So there are still industries that cater for good food and clothes, nice-looking dwellings, books, entertainment and such. There are new industries: agencies that will pray for you in case if you and all your friends at once are killed, ported to another plane where deities have no reach and/or lobotomised; agencies that hide your friends connections so they cannot be traced and destroyed, prayer farms where indoctrinated quasi-humans are taught to pray for mass production of wonders - it is noted that in direct confrontation of two prayers the one with more people behind it wins for a time; prayer farms became a way to bring some permanence in the world where everybody can do everything. Crime industry is mostly concerned about what cannot be replicated by miracles, such as good food and clothes.
The world still have problems. Overpopulation is the one: the world is huge but the reach of the deities isn't that great beyond it and nobody wants to move to outskirts where prayers aren't that well-heard. Emotional climate is another one, because it might take one angry teenager to blow up half-continent and, while people will be prayed back in due time, it is not a terribly welcomed event. Stagnation is a bit of a miffle too, as there is no reason to invent anything, really, and what is new and invented tend to be mass-duplicated instantly robbing the inventor even of the credit and control over their inventions.
But yet, the world is much better with deities. Humanity is much happier now. At least the deities think so and they aren't going to go away anytime soon in all eternity.
All is good.
This is actually a background for the demon/fey dimension. Not Abyss 'blood-blood-war-war' type, although with some tweaks it might be this too, but more of Exalted: Malfeas type, only even more bright, decadent and indulgent.
One of the things that wondered me when I've read through it is that demons in Malfeas pray to their Yosies just a humans pray to their gods. And humans, as you know, might become a bit of ass when given power. So what if all humans in certain world were given almost unlimited power via the very simple and only partially limited means?
It is a world where nobody is hungry but everybody is somewhat bored so they go into different worlds via special channels (so not to lose all of their connection to wish-granting deities and safely go back) to have fun - like a billionaire going slumming, in essence, because after millennia of deities benevolence 'fun' might have a very strange meaning to these humans. Pain might mean little to you if your 3-years old sister inflicted 'Blade Barrier' on you just because she wanted to play with your toy train.
Powers are kept to cleric list, so the exact scope of deities influence is adjustable but every regular non-impeded human (however you define 'human' in your world) has full access, at will, to all clerical spells to cast them as level 20th cleric.
For example, 'Miracle' in Pathfinder can emulate any other spell of 7th level or lower - obviously with this approach only highest levels of arcane will be a true rarity as arcane keeps working by regular rules. For example, with this you have a full access to polymorph and shapechange spells, so humans can look pretty much however they want. It will change if you use ADnD 2Ed list where 'Miracle', as far as I remember, doesn't exist, so shapechange would be something more rare - maybe even a new industry.
But clerical lists in all settings I know about give healing and resurrection. As DnD demons cannot be fully killed by most accounts, it fits rather well to imagine that they just prayed back by their friends.
'Buddy system' becomes so much more important for a demon. Even you are lobotomised (so you cannot pray yourself any more), transported to another plane where deities cannot hear you, buried alive so you resurrection will causes more torment, and variously killed, if you have a buddy to say a simple prayer for you, all this can be reversed to full health. 'Facebook' in the demon world will be like a life insurance in a sense it insures the continuation of life. Slander, libel, gossip and other social weapons would be much more dreaded.
It was fun to imagine demons to be very social in their own world, although in other worlds they are more like 4chan for 1% who just loves to rub it in. Continuing internet analogies, Erra itself would be a bit like wikipedia without moderators - 'truth' defined by the last edit and everybody can edit it, no locks but a lot of edit wars (deities all have a very short attention span and impose almost no judgement on a prayer so they will grant a counter miracle as soon as somebody prays for it; your Italy might be not yours for long.)
Why social hierarchy still exists and how exactly it might look like is a hard thing to figure. I know humanity will figure out somehow how to create a enforced hierarchy with privilege and punishment even when everybody casts 9th level Miracles at will, but I cannot see exactly how at this moment. People with non-replicable powers might be on top and anonymity might be another pillar.
By my idea the deities aren't evil and/or sinister (actually they are supposed to be Very Dumb Very Good if alignments are concerned) but they are stupid, friendly, alien enough just to be an inconvenience and to spawn conspiracies, very naive and are granting without limits. Depending on what is needed from demons, humans might be essentially immortal (because deities are easy to talk into giving another go on a life after a brief respite) or still have a somewhat limited lifespan because deities cannot reach that far. The second approach will create a more nuanced world but with first you can truly create an endless horde of Abyss if you so wish.
Demons also have a lot of at-will powers (in particular summoning more demons), are terrible looking and are hated by gods of other worlds (clerical powers such as 'banishment' as an example). The first might be a 'umbilical cord' kind of thing, that prevents the human of Erra coming with their full powers into another world but retaining some channel to be able to go back. The second and the third are because gods might be a tad afraid of Deities' influence spreading to their own world (Erra might be a merged dimension that slowly expands) so they literally demonize humans into terrible shapes to prevent 'halo effect'.
'Erra' isn't a particular world, but a placeholder to somehow reference a place where this is happening. It might be 'Terra' without 't', it might be 'Error' or 'Errant', doesn't really matter.