Practically nothing is known about Them except that which they have left behind. Their symbol as shown above appear wherever they have been as do their writings which twist and writhe as with a life of their own. Writing which, far below the lifeless desert of an alien world, almost killed Alexander.
That is not all they leave, however, if only it were.
They leave dead worlds, whole populations debased and desecrated in death, abused and made party to acts even the worst of pyschopaths would shy away from.
And they always leave a witness.
How they choose the poor soul who is honoured to watch everyone he knows and loves die is unknown but they will carefully cut off her eyelids and leave her, with drying eyes, to watch the butchery, the rape, the sacrilege, and the torture. They will raise their crystalline 'trees' of barbs, thorns, and hooks and impale those begging loudest for death upon them and...copulate beneath the rains of blood. All while the chosen survivor is forced to watch and lose their sanity, one depraved act at a time.
They leave the poor soul, too broken to even end their own life, alone among the dead and their nightmares. They take nothing of value, no slaves or tribute, they simply come, carry out their atrocities, and leave nothing but their witness alive.
On a nameless moon, close to the ruins of one of humanity's Arks, Kalliades and Neshaa met one such soul on their pilgrimage to find Alexander. All he could say, over and over, "They are coming. They are coming.They are coming..." heartbrokens, Neshaa gave of Ahura Mazda's peace to that ravaged boy.
When, upon reuniting with Alexander in deep space, in orbit around another nameless moon, they boarded the Hyperion's Bane, a Kalshodar cruiser long lost, they saw a horror so terribly familiar in the main embarkation deck of that ship. They saw Lysander and his entire company of Kalshodar impaled on those same "Trees of Pain" as Lupernikes called them. The hanging Kalshodar healing around the vampiric thorns of those trees of living crystal before being ripped, torn, and bled once more. Nobody had heard a Kalshodar scream like that before, not even Apàteon when he vivisected them below the streets of Lùndùn.
The Kalshodar, Dracograth, and epibatoi making up the boarding party were torn from their sickness and horror by Alexander's calm command "Burn it all," he said quietly. "Burn it with everything you've got."
Only those who knew Alexander well knew this was a sign that he was in a place far beyond rage, the almost grey cast to his eye confirmed that. They would burn this place or he would tear it down with his bare hands. They set their charges, gathered up the scattered armour and weapons, and left the Hyperion in silence. Minutes later, The Dragon's Crown and every surviving cruiser blasted the Hyperion into the system's sun, that their brothers might go to Elysium in peace at last.
Alexander has been fey since that moment, moody and withdrawn, even from his closest friends as the journey to Gaia progresses. "They are coming," he will murmur on those rare occasions he speaks at all. "They are coming."