A Dark Angel

A single Astartes resided in a shrine room within the ominous halls of Watch Fortress Erioch. In service to the God-Emperor and to the Inquisition, the obsidian-clad superhuman laid on a single knee, his silver arm glinting in the well-lit room. The seal of the Inquisition laid upon the left shoulder, but the right bore a green shoulder, with a white pair of wings and a sword lying in the center. The Marine lowered his other knee and laid upon the ground with his shins against the floor. He was poised in such a way to look like he was venerating the figure before him.
A hero of Deathwatch, clad in ornate Artificer Armour and with the dour, frowning vox receptor that was the hallmark of the Mark VII Aquila helmet. Intricate patterns laid upon the stone figure's steel and ceramite armour, and his gauntlets crossed over each other, both of his hands lying upon the pommel of a Thunder Hammer, one of the rarest of Astartes weapons. Behind him laid the pauldrons of every Loyalist chapter in service to the Imperium. The Dark Angel did not know who this anonymous Marine was - he was very likely a Blackshield, one from millennia ago, perhaps from a Chapter that was shamed by its actions. Or perhaps he shamed the Chapter, and was sent to serve in Deathwatch, to redeem himself.
The Dark Angel's helmet tilted towards the Ultramarine pauldron that laid upon the wall, with the Red Scorpions shoulderpad lying underneath. This sparked a thought in his curious and inquisitive mind - how did the Imperium survive, for so long? It could not have been the Space Marines alone, nor the Imperial Guard, or the Sisters of Battle, or every other force in service to the God-Emperor's rule. Was it their faith? Their beliefs? Their wargear?
No. It was their courage.
His eyes shifted back to that of the Ultramarines pauldron.
That was the Ultramarines battlecry.
Courage and honour.
Or at least it was, before the Invasion of Macragge. The Dark Angel was uncomfortable around the blue and gold Astartes, at times, thanks to their conservatism and habitual shoving of the Codex Astartes in other Chapters' faces, which he reserved one of his own words for them: "Codex-bashers". He did not loathe them, however. Before his second vigil, he met an Ultramarine who eventually overcame his traditionalism, and hailed him as a hero to the name of the Adeptus Astartes. He suddenly felt a little better remembering that, considering said Marine chastised him when they first met, thanks to the Dark Angel's unorthodox tactics. But a Chapter like them also represented something in the Imperium. Something that mankind could aspire to be. Heroes. Saints. Noble warriors, like what this Angel wished his brothers could be, what the reputation his Chapter was trying to uphold. But they did not listen to his words of caution, for he was too naive to have his cries answered. Still, after two centuries, that is what they thought of him.
The amber eyes that laid behind his helmet turned back to that of the Deathwatch champion who stood, stalwart, staring out into open space. The Dark Angel unsealed his helmet and took it off, revealing a long, flowing black mane, ivory skin, and a matching beard. His eyes burned with an intensity that seethed with purpose and content. He was a Dark Angel, that, unlike that of his brothers, was noble and performed humanitarianism where he could, rather than the aloof grimness that the Dark Angels bore like a badge of honour.
He slowly rose to his heavy boots, standing almost as tall as the statue itself. He was a giant, even by Astartes standards, standing a full two feet and eight inches taller than most Astartes, at nine foot eight, just about the size of an Ogryn. He turned back from the statue, and crossed his arms over his chest, forming the Imperial Aquila as a salute. He began his trek out of the room, his boots thumping against the ground with a greater intensity than that of normal. His contemplation grew, remembering the old fable that lost Calibanites once recited.
And the Angels of Darkness descended on pinions of fire and light... the great and terrible dark angels.