A/N: OK, before I begin this chapter, a few words. The knowledge I have of Warhammer40K is extremely shallow. Basically, I only know that the Space Marines are pretty OP, that they will kill and destroy everything that isn't fully human, and that the Warp can fuck things up pretty badly. I literally just looked up which chapter was in the "Project Astartes" fan movie and went with it. Now onto the story:D
They shall be my finest warriors, these men who give themselves to me.
Like clay I shall mould them and in the furnace of war forge them.
They will be of iron will and steely muscle.
In great armour shall I clad them and with the mightiest guns will they be armed.
They will be untouched by plague or disease, no sickness will blight them.
They will have tactics, strategies and machines such that no foe can best them in battle.
They are my bulwark against the Terror.
They are the Defenders of Humanity.
They are my Space Marines and they shall know no fear.
~The eternal God Emperor of Mankind~
Black Lake, 6th June 1994
Harry was desperately trying to fend off The Dementors to save not only himself but also his Godfather Sirius Black. He poured every ounce of strength into his Patronus spell, but the horde of Dementors wouldn't give up.
He gasped for breath and broke the spell, even with everything he had, it wasn't enough. Two particularly large Dementors slowly closed in on himself and Sirius, knowing that their Prey couldn't fight back anymore, but just as the two demons prepared to kiss the humans, something happened.
It looked like an explosion went off in the Black Lake, a giant mass of water was suddenly violently thrown into the air. This unexpected and inexplicable phenomenon caused even the Dementors to pause and look at the spot that just went off.
Before Harry or the Dementors could do anything, numerous blue lightning bolts shot out of the water.
Harry watched in fascination how the bolts disintegrated the Dementors completely, something widely regarded as impossible.
After a few minutes filled with zapping sounds and horrifying screams, silence returned, but not for long.
Out of the water came…trolls? They certainly looked similar in the moonlight. Giant beings with wide shoulders. But there was a metallic rattling coming from them, so they must be wearing some kind of armour.
Harry snapped out of his awe when two heavy footsteps stopped right before him. He slowly raised his head. Giant feet, clad in dark grey metal. Long and thick legs, followed by a wide torso, giant shoulder coverings, and massive arms. The head of whatever this was looked like a skull and the eyes were covered by black glass, which made it impossible to see the eyes.
"Brother" rumbled a deep voice from nearby, "it seems that the Warp has transported us through time. According to our systems, we're on holy Terra, in 994.M2"
"That's long before the Emperor united mankind. But" the being in front of Harry turned around and looked at the other beings that stood nearby "It seems that even in these ancient times there were mutants" It then pointed at Harry "and heretics. You know what that means!"
"BURN THE HERETIC!
KILL THE MUTANT!
PURGE THE UNCLEAN!" cheered the others and raised what looked like guns.
"IN THE EMPEROR'S NAME, LET NONE SURVIVE!" finished the one in front of Harry and raised a strange-looking sword.
"WHAT IS YOUR DUTY?" He then asked.
"TO SERVE THE EMPEROR'S WILL!"
"WHAT IS THE EMPEROR'S WILL?"
"THAT WE FIGHT AND DIE!"
"WHAT IS DEATH?"
"IT IS OUR DUTY!"
"FOR THE EMPEROR!" Cheered all of them together and ran into the Forbidden Forest in squads of five.
Only the one in front of Harry didn't move. He pulled out a gun and pointed it at Harry.
"Don't be sad that it ends like this for you. Be happy and grateful that you get purged by us, the chapter of the Retributors. Let us guide you into the Emperor's eternal light" and then he pulled the trigger, and Harry's world was engulfed in darkness.
Only to become light again when he woke up. The Retributor was still there and the barrel of the gun was still smoking. The giant man growled "Chaos scum! Die by the Emperor's wrath!" And he shot Harry again, this time, the Boy Who Lived didn't rise again.
Space Marines are amongst the worst enemies you could face. Their armour is thick, their weapons mighty, their devotion absolute and their methods ruthless.
They needed seven days to purge the magical world completely. Nothing could resist them. Wizards and witches got burned, the Goblins were mowed down, Dragons and all other kinds of magical beasts were slaughtered like cattle.
Even Hogwarts and the Ministry, Voldemort (still only a spirit) and the Death Eaters were hopelessly destroyed.
Even Millennials before it existed, the Glorious Imperium of Mankind defeated the Xeno threat. In the Name of the Emperor.
"Why would the Eternal God Emperor of Mankind grant us strength, if not to use it to protect those who lack it?" That was the Mantra of the Space Marines, the Astartes. Normal humans were weak to them, and everything else was a threat. So they protect the weak by destroying every threat.
After they burned the heretic wizards and witches, killed the mutant beasts, and purged the unclean Goblins, the order of the Retributors went into sleep, thanks to their unique biology.
They went to sleep, fully realising and willing to wait over three dozen millennials until they would be woken again, to once more serve the Emperor as loyal tools in the endless war against Chaos and the Xeno scum.