A Bloodthirster...

Kais had heard about these, but only in gibbered tales told by what he had believed to be madmen, but now one stood above him, and it looked very, very , real...

The Bloodthirster, greater daemon of Khorne, towered over him. Its stature took it to the foreground of vision, any other sight in the cavernous room seeming like mere optic ambience, no matter what visions they held. Kais did not notice that all other marines had fled. The daemon was the breadth of a tank, and it eyes, surrounded by shredded skin, burned with an unholy fire. To look in to them caused a pain the like of which Kais had not experienced. It carried archaic weapons decorated with evil sigils in its arms, which were covered in gaping wounds. Kais raised his bolter, and fired.
The Bloodthirster absorbed the shells into its chest, and laughed. Clearly it was not afraid of gunfire. Kais had soiled himself, but he did not give in. He continued to fire. The shellls, blessed by the tech priests of Mars, flew forth from his weapon at a massive pace, the cracking reports of the weapon blending together. The Bloodthirster continued to laugh, shrugging of the shells like a human would treat vaguely irritating flies.

It looked directly at Kais, and he experienced a burning. It seemed to be coming from behind him....

He saw a massive glow which blinded him, and heard strange and muffled shouts...

And then he knew no more...