It is the Great Crusade, M31, on a long-lost human world being conquered by the Imperium. In the ruins of a city, you see a Space Marine up ahead...a World Eater, wielding a chainsword and bolt pistol. His sword and armor are coated in the blood of those who defied Imperial Compliance, and he laughs with glee as he crushes a fleeing dissident underfoot. Butcher's Nails implants gleam on his scalp as he looks up at you with a maniacal grin, his voice grating.

Aha ha! He blasts another dissident apart with his bolt pistol. Blood for the Emperor! Kneel before him! He drives his chainsword through the torso of a wounded dissident on the ground. Or die as his enemy! He casually kicks a car into a storefront being used as shelter by dissident civilians, killing all within. I love being the good guy.