Spastic twitching movements, and a body too pale and thin to still be human and alive still. Eyes glowed with the purple un-light of the Warp, and under that pale skin, tiny scuttling things moved.
A hand moved through the rock, in a flamboyant gesture; this form was only a projection, and so it literally passed through the rock.
A towering and superhuman looked down, as stoic as the rocks and a volcanic fury burning within. Great green mechanized armor, adorned with the images of fierce dragons, made the giant's form even bigger. The Imperium's sigils were blazoned upon him, and honor scars branded his face. He blinked, the red light blazing from his eyes flickering slightly, and on his coal-dark skin, it was as though he were a bit of the lava of Nocturne itself that had shaped itself into the figure of a man, but nobler and more heroic.
At his side was a chainsword. On his pauldron was the iconography of the Fire Drakes company of the Salamanders Chapter of the Adeptus Astartes. Thus spake the Salamander, the God-Emperor's own angel of mercy, "You know you cannot escape me, daemon."
The daemonhost grinned, and worms dripped from his mouth when he spoke. "You truly are a stubborn knight-errant, Astartes."
"Dedication is the least that I owe the Emperor and Vulkan."
"Such loyalty to a rotting corpse and a mutant long since lost to the Eye of Terror itself. It is almost endearing."
The Salamander's eyes burned hotter. "Take care how you speak, daemon. Your death is certain, but it may yet be worse than anything even you can imagine."
"And yet I imagine so much."
"Do not tempt me." The Salamander's words were even, but stern.
"Such dedication, conversely, is gratifying. You may yet have much to offer Tzeentch-"
"No."
"-By his will your people may yet survive-"
"No."
"-And I do believe that you have so much courage-"
"The answer," The Salamander said in a voice of iron. "Is no."
For a moment, the daemon was silent. It spat, "Your Emperor is a rotting corpse. Your people offer prayer to a corpse-god!"
The Salamander's expression flickered, only for a moment. In that stoicism, there seemed a rage fit to split the world itself in it's fury. "Even a man who has nothing can still have faith. Duty alone sustains even the most lost of the God-Emperor's people."
"So stubborn, Astartes. I must wonder, why do you hound me so?"
The Salamander considered. "…Four months ago. There was a city thirteen miles from this cave. You were a daemonhost summoned there. You killed your captors, you killed their families, you killed every living thing there down to the last rat. You burned it to the ground, and cast the remnants into the Warp."
"…Why should you care?"
"Someone must!" The Salamander snarled, composure breaking. "I will!"
"But why?" The daemon looked genuinely peturbed. "I do not understand."
"…You and your kith have spoken of darkness. Know this, Warp Horror… I know darkness. I was born in darkness. Raised in darkness. Until the sky was a dream, and the sun a myth. I remember the deep darkness, warm and soothing. The light of the magma flows powering the forges and alighting the songs of creation passed down to us by the Mechanicus and Vulkan himself.
"I was a boy when the Time of Trails came, when Nocturne burned in volcanic fury and earthquakes devoured all they could. My cavern died. My family died. Everyone I ever knew died." His eyes gleamed. "I did not. They who became my battle-brothers found me, and they knew the same lesson I learned down there, in the safe places below Nocturne's surface."
"And that is?" The daemon said, fascinated.
"That life… and life alone… is the most precious thing we can ever know. The life of humans, the life of machines, the life of legacies and reputation. That victory over the God-Emperor's enemies is desirable, but the preservation of the lives of his people, of all the people upon all the worlds of the Imperium, that is the purpose of the Adeptus Astartes. That was what I, made from Vulkan's own gene-seed, was made for. That all my battle-brothers was made for." His eyes burned. "I will see the lives you took avenged. And one day, you and the foul gods you serve… will burn."
"I still don't understand why you care so much," The daemon confessed.
The Salamander snorted. "And that is why you must burn."