"The Ossiarch Bonereapers are Nagash's new vision of the Mortal Realms"
Personally I would of painted these guys in blue...
via the Warhammer Community
https://www.warhammer-community.com/2019/10/19/what-is-the-tithegw-homepage-post-3/
Nagash has a plan. This plan needs a deathless army or two to accomplish it. To build a deathless army, The Supreme Lord of the Undead needs some raw materials – which is where the tithe comes in. As we draw closer to the release of the Mortal Realms’ latest army, we’re taking a close look at the fascinating lore of the Ossiarch Bonereapers.
The Basics
The Ossiarch Bonereapers are Nagash’s new vision for the Mortal Realms. Unlike the Nighthaunt or Flesh-eater Courts, they aren’t risen revenants or deluded cannibals, but a brand-new form of unlife, purpose-built for war. Only the Mortarch Katakros and his chief lieutenant, Arch-Kavalos Zandtos, possess true memories of their time among the living, with the remainder of the Ossiarch legions consisting of consciousness formed from combinations of dozens or even hundreds of mortal souls. These are then used to animate immortal, inviolable and horribly strong bodies constructed from bone.
The Ossiarchs are Nagash’s future vision for the Mortal Realms. He intends to create a perfect, endless army spanning every landmass, with everywhere from Azyr to Aqshy rendered into a cold, unfeeling metropolis known as the Necrotopia.
Which is where the tithe comes in.
The Tithe of Bone
The Ossiarch Bonereapers already possess massive armies, having carefully waited out the apocalyptic devastation of the Age of Chaos. However, Nagash’s ambitions of conquering the Mortal Realms require even more warriors, and for that, he needs a lot of bone.
Sure, he could just send his armies out to slaughter every living thing they found, but that would be unsustainable, not to mention pretty messy! Instead, the Ossiarch Bonereapers first seek the most deadly of weapons to accomplish their goals – diplomacy.
The Tithe Begins
The Ossiarch legions are no mindless automata, but intelligent, independently minded and cunning. While driven by the purpose for which they were designed, high-ranking Ossiarchs, like those of the Mortisan caste, are capable negotiators, schemers and manipulators, bringing empires to their knees by word and contract as well as fire and sword.
Upon finding a settlement of the living, the Mortisans will present an offer – tithe your bones, or face annihilation. Where the offerings come from matters not to the Ossiarchs – some civilisations may dredge their graveyards for fitting tithe, while others may choose to take the limbs of their citizens in order to supplement a dangerously meagre collection of remains.
The Cycle Continues
As the years pass, the Ossiarchs will return time and time again to civilisations they tithe from. Sometimes, vast spans of time may pass before they come again, as Ossiarchs that made deals centuries ago come asking for bone in ancient dialects now unfamiliar to a land’s inhabitants.
Generally speaking, the tithe is cruel, but sustainable – the Ossiarchs wish no more to slaughter wantonly than a farmer wishes to slay his cattle. However, capricious commanders of the Stalliarch Lords are known to issue impossible terms to empires they wish to destroy, such as requiring exact records of the condition of every bone kept in the city – including those currently residing within its citizens.
Forged of Bone
The Mortisan’s use of bone is not accidental – indeed, the properties of the matter used to create an Ossiarch Bonereaper shape both their character and their abilities. The Petrifex Elite are forged from fossils, making them ponderous, single-minded and nigh-indestructible. The Null Myriad are forged from those skeletons used in the construction of the Black Pyramid, giving them a terrifying resilience against magic, and a quiet, unnerving pride that unsettles even the champions of Chaos.
Perhaps the most terrifying are the Ivory Host. Outwardly magnificent and noble in aspect, these warriors hide a dark secret – forged from bestial bone, they give in to a horrific animal rage in battle, clawing and hacking at their enemies as the bestial energies within their bodies take over.
The Tithe Broken
Of course, the tithe cannot go on forever. Any empire that falls victim to the whims of the Ossiarchs is doomed, either by the eventual, inexorable expansion of Nagash’s domain or by their own foolish defiance. Should any try to resist the demands of the Ossiarch legions, either by outward aggression or by providing poor-quality tithes, they are slain.
When dealing with tithe-breakers, the Ossiarch Bonereapers attack with terrifying force and impeccable discipline, stopping only when their betrayers are utterly annihilated, remains left to flap and flutter on long spears in warning to other would-be rebels.