Anyhoo, I'm now being forced to sit down and flesh out/codify all the things. I'll present them in no particular order. Expect 5e flavored with OSR.
Here's the lore!
A long, long time ago, Mother Sun and Father Moon created the world from nothing. They sculpted the mountains, dug out and filled the oceans, scattered pockets of precious ore, and seeded the world with life both sedentary and mobile.
They wanted more. What good is art without intelligence to appreciate its nuance?
So they gave up their physical forms, molded beings strong, tall, and wise out of their own flesh, and filled these shells with ephemeral, flickering energy plucked from the void.
These elves, the first sentient creatures, gave the gods the adulation and validation they sought and created many wonders in their time on the earth.
Eventually, the elves began to experiment on their own and the earth around them, reshaping flesh and spirit at a whim, working towards unlocking the secrets of the world and turning away from the gods.
Caught up in their perversity, the enraptured elves ignored the warnings and pleas delivered by Mother Sun and Father Moon, so the world burned. Proud metropolises of spiraling wood and tempered adamant sunk into themselves while the elves screamed their pain into a cold, uncaring void.
Afterwards, however, Father Moon felt guilt over his rashness. He spoke to Mother Sun about bringing back the innocent and kind, but in her pride, she refused, and spoke of a new race of beings she planned to bring forth, both humble and mighty.
She spurned his advice, and he refused to help her.
Father Moon, tormented by the screams of his children, raised the few he deemed worthy of life, but without the spark of Mother Sun, they returned as shadows of their former selves, as vampires, forever craving the warm flesh of the sun.
Mother Sun, ignoring her own pain and guilt, brought forth the angels to inhabit a scorched earth, but without the soft glow of Father Moon, they emerged bright and terrible, forever lacking the softness of the moon.
Each god, upon seeing the abominations the other had wrought, began to argue and then spar, invisible hands pummeling the fabric of the world.
As the gods fought, the vampires crawled out of the ruins of their homes, and the angels descended from the skies on flaming wings. Each side was seized with a terrible hunger, and each fell upon the other, ripping and devouring.
For years, the skies blackened, twisted, and split open.
When the fury of the gods abated, bleeding and broken, they looked upon a world burned at their hands and riven by their creations. Remorseful, they decreed that never again should gods fight each other, for to do so was to neglect their responsibilities as creators. Mother Sun tended to the hurts of her remaining angels while Father Moon healed his few vampires of their wounds.
United, they named their world Requiem, in honor of the dead, and one final time conjured clouds of life-giving rain to heal and erase the awesome sprawls of ruin. This last work done, Mother Sun, Father Moon, angels, and vampires retreated from the face of the earth, sick of war.
While each god promised that they would never again birth a race, the legacies of the elves persisted. Ancient vaults, built secretly to resist the powers of the gods, opened, unleashing new spawn birthed of godflesh upon the world.
Humans, dwarves, and orcs, the three Founder Races, spidered out across the world, rediscovered metallurgy, writing, agriculture, and settled atop Requiem, a graveyard for billions.
Their children, known as halflings, goblins, gnomes, and ashanti, forged their own distinctive strains of civilization. Wars flared up, as they always will, but wars of swords and spells, not wars fought with weapons capable of scorching the world.
New gods arose, offering knowledge and power, garnering devoted flocks. Advances in tech and magic improved both standards of living, trade networks, and the lethality of wars. Mighty dragons awoke, and carved out places for themselves.
Eventually, though, Mother Sun and Father Moon turned their gaze back to their monument, and were shocked by the proliferation of new life. The angels and vampires awoke, charged by their creators to walk among the races and learn their ways. What they discovered changed them.
Some vampires, wishing to redeem themselves, began to teach and guide the new races of the time before, dribbling out scraps of knowledge and caches of technology, seeking the blessing of Mother Sun. Some vampires, seeing a chance to live again, shed their former identities and walked among the new flesh, rejoicing in both familiar and unfamiliar sights. Some vampires, bitter over the loss of their world and their new form, disappeared into what old vaults of the elves still existed and became something worse. Darker.
The angels, offended by the new gods, descended to convince the new flesh of the old gods and their power. Some succeeded, and established bastions of Mother Sun. Some were conversely persuaded of the righteousness of the new gods, and broke away from Mother Sun. A few simply discarded all bonds like old robes, and took to exploring the world both old and new.
Eventually, the puritanical angels, hurt by their more “enlightened” brethren, demanded a meeting to refute the usurpers. Both sides brought mortal supporters, and sought neutral mediators. An agreement was reached: seven vampires would serve as the mediators, and each side would respect what the seven decided.
Maybe a mediator sought war. Maybe a mortal supporter decided to take matters into their hands. Maybe an angel betrayed the terms of the contract. Whatever the case, the negotiations broke down with the assassination of a puritan angel, and an angelic civil war erupted.
Father Moon and Mother Sun, afraid of the damage divinities could do, prevented any gods, new or old, from taking part as armies lead by screaming angels clashed over entire nations. Atheist states attempted to distance themselves from the fallout while neutral angels and vampires were pressured to take sides.
The vaults of the elves, perhaps tampered with, perhaps sought out for their ability to decide wars, birthed one last, horrific thing: demons. Hordes of slavering, whining, cringing, starving bundles of twisted flesh began to feed upon the armies of both sides.
Eventually, the waves of demons were forced back, but not before mortals learned how to control and summon them, and not before especially powerful individuals, bloated on souls and biomass, laid claim to the title of demon lord.
In the wake of the demon war, society started to rebuild. New alliances were formed, formerly verdant lands were abandoned or burned to purge demon infestations. Most major metropolises survived the conflict, notably the unlikely confederation of Bblyns and Torre’kan.
The present is a more cynical time for mortals. Some people cling more strongly to their gods than ever, hoping for protection and deliverance, while others reject deities. Angels are viewed in the same light as deities. Vampires are distrusted for their dietary restrictions and history but reluctantly accorded respect for their knowledge and proven leadership. Most alliances center around the military containment of demons or the turf wars that occasionally flare up.
The new art of devilry has attracted support and controversy like moths to a flame. Some argue for its expansion, others for its immediate cessation. Demons are demons, no matter how they’re bound.
Following the demon war, most angels have been ordered to pay penance. Some have renounced arms and dedicate themselves to helping and protecting the innocent. Some pledge themselves in service to an organization, and some have willingly locked themselves away.
A select few angels have discarded all allegiance, believing themselves betrayed. These angels look for answers, like some vampires before them, in the treacherous vaults of the elves. Some return, chastened, sporting new scars. Some never return, but tales spread of beautiful and terrible beings of flame both glorious and grotesque.
Nations rebuild as they always have around war and trade, two sides of a coin. The new gods, kept from fighting and deprived of their angels, work through mortal proxies. Throughout all this, Father Moon and Mother Sun observe, occasionally working small changes in the world towards their own inscrutable goals.