In a time before time, there lived the Avvim. They were a people tall of stature and simple in their ways. The powers of the Celestial Spheres took interest in them, and so assigned a host of angels to observe them, but forbade to interfere in their lives. Yet soon these Watchers came to adore the mortals, and at last descended in their full splendor upon mount Hermon, and made themselves patrons over the Avvim.
From the Watchers the Avvim learned countless secrets and trappings of civilisation. Arakiel taught them to divine the signs of the earth, Ezekiel - of the clouds, Kokabel - of the stars, and Shamshiel - of the sun; Semyaza bestowed upon them the lore of herbs and medicine; but Azazel's gifts were the greatest and most terrible of all, for he gave the Avvim the knowledge of weaponsmithing and warcraft.
But the Watchers came to love Avvite women most of all, and took them as consorts. Soon there were children of angels walking the earth; these were the Nephilim, mighty men of renown, gigantic, pale, horned and six-fingered. They were most learned in the arts of their fathers and made themselves the first kings over the Avvim. But their origin from a forbidden union cursed them with a terrible hunger and a foul temper, and they ate the flesh of their subjects and drank their blood, and the earth was devastated by them.
When the Celestial Powers came to know of this violation of their decrees, they were furious and in short order imprisoned the Watchers in Sheol, bound by fetters tempered in the blood and tears of those who suffered from their gifts of civilisation. But they coud not do the same to the Nephilim, for they were of this world, unlike the angels. Nonetheless, the Nephilim's curse soon took its toll, as they feuded with each other and killed and devoured one another, and the remaning ones lost purpose and wandered into the wastes. Only their descendants remained to take their place; these Rephaim were lesser than their fathers, and with every generation the might of the sons of the Watchers waned, but so did their hunger.
Now there are but a few families of pure-blooded Rephaim, and even the Avvim are not many. Instead, humans have multiplied in foreign lands, and several tribes have even migrated into the lands of the giants, though the giants still rule. Recently, a great golden bull has started to speak its will as a new god, and the last giants have become priest-kings and sacred warriors. The bloody arts of the Nephilim have been rediscovered, and the new temple runs red with sacrifices to the Watchers, to the Nephilim and to the goat-demons of the desert. And today's ritual is the most grand yet, for with the blood of hundreds the high priests hope to break the celestial decree that binds the Watchers to the underworld, to let them once more walk the earth and bless it with their gifts.
This is some fanart for the game Dominions 5, although the story in the game is largely based on the apocrythal Book of Enoch, as well as on general Old Testament lore about Canaanites and such.