Disclaimer: I own no franchise mentioned in this work. Halo belongs to 343, Doom to ID.

Fair warning, this fic does contain light spoilers for Infinite. Nothing particularly substantial in regards to story points, mostly because Infinite doesn't seem to contain much of anything that can actually be spoiled anyways. Good game, but for a $60 campaign it is woefully empty.

This story reveals the title of a new faction introduced in Halo Infinite. It's underwhelming.

The bottom author's note gives a little more detail about them, but the game didn't even reveal their name that I could find.

This fic makes far more sense to those who have played Doom 2016, Doom Eternal, and Halo Infinite. It's readable otherwise, but a lot of what is going on will probably be lost.

In the first age, in the first battle, when the shadows first lengthened, One stood.
He chose the path of perpetual torment.
In his ravenous hatred he found no peace, and with boiling blood he scoured umbral plains seeking vengeance against the dark lords who had wronged him.
Those that had tasted the bite of his sword named him...
The Doomslayer.

When humanity first breached the confines of their solar system and exploded out into the interstellar expanse, they had been ecstatic. After millenia of development, conflict, and generations of looking to the stars, Slipspace finally gave them a means to explore that great unknown. It was only a matter of years until dozens of planets were colonized, their inhabitants fighting for existence amongst the unforgiving universe before them.

Yet, even as humanity expanded into the galaxy, they sought better methods for doing so. Faster transport, larger ships, a more reliable source for energy. It was this pursuit that led them to find Argent Energy, a discovery heralded as the next great technological achievement. For all the good that Argent may have brought, the consequences did not take long to appear as an entire planet was destroyed by what could only be called Demons.

Conjured from Hell and left uncontested, the mortally challenged might have overwhelmed the entire galaxy given the chance. Fortunately for humanity, this was not so as the legendary warrior only known as the Doomslayer appeared and single handedly fought back the menace. It was only the valiant actions of this individual that saved humanity from damnation, but he disappeared into the last portal to Hell and was never heard from again.

Of course Chief knew of the Doomslayer, but the warrior of legend was just that. Centuries later, with the Covenant bearing down on humanity, the Spartans had attempted to take up this mantle. It was only through enormous luck that they had survived, and yet even years later humanity was still struggling for survival. The Demons, the Covenant, the Banished, the Created, each had tried to crush humanity and each had failed.

Now the Harbinger had released the Endless, a threat told of as greater than that of the Flood. Regardless of the doubt he held about that statement, Chief had risen to fight them as was his duty.

The nature of his enemy became clear quickly when a horde of Demons had descended on Zeta Halo, looking to annihilate everything. For all that he fought and killed, even Chief could not hope to fight the Endless legions of Hell.

Against all the evil that Hell can conjure...
All the wickedness that mankind can produce...
We will send unto them only you.

Looking up into a visor similar to his own, the Chief could only conclude that the deep, rumbling voice came from the being standing before him. Clad in green power armor and wielding a double-barreled shotgun, the unmistakable figure of the Doomslayer himself looked down upon the exhausted Spartan. For only a moment the rictus of hatred on his face faded as the legendary warrior glanced around at the carnage that had been wrought.

It was clear that the Demons had learned to fear the Doomslayer, their advance momentarily halted after he had torn through their ranks. Confused as he was by the continued survival of the legend, the Master Chief could respect the reputation and prowess on display. As the Slayer turned back to him, their eyes met as each examined the other with the careful analytical gaze of a warrior. Even feeling weak and with the numerous injuries gained from the fight, the Chief held his head high.

A gauntleted hand suddenly appeared before him, hauling the Spartan to his feet with ease.

Swaying slightly as the Slayer let go, the Chief looked up only to find a glowing blue crystal being held out towards him. Looking up in confusion, he watched as the Doomslayer clenched his gauntlet as if crushing the crystal.

Figuring that his luck would see him though, Master Chief copied the action, applying tremendous force to shatter the crystal into wisps of energy. The Spartan took in a deep breath as he felt his injuries fade, old pains leaving him as MJOLNIR itself seemed to grow more powerful. Panting slightly from the unexpected rush, Chief caught the slightest nod from the Slayer as he once again hefted his shotgun.

As a cacophony of demonic howls reached them, the Chief glanced their way for only a moment before swiping his assault rifle up from the ground. With his ammo and health somehow restored by the strange crystal, the Master Chief looked to the Slayer and returned the nod. He would continue his fight, in this world and into the depths of Hell itself, much as the Doomslayer had done for hundreds of years before him.

Seemingly satisfied, the Doomslayer let out only a single sentence, "Rip and Tear, until it is done."

The Endless descended upon them then, the demonic legions pouring from portals that dotted the ring. Yet, they would not see victory this day, for every one of their number that fell merely strengthened the two warriors. Together, the Slayer and Spartan marched forth, driving the menace back into the fiery abyss, the legends of the Hellwalkers only growing as they sought vengeance against any who dared stand in their path.

Tempered by the fires of Hell, his iron will remained steadfast through the passage that preyed upon the weak
He set forth without pity and hunted the Endless with barbarous cruelty
For he alone could join the Slayer, the title of Demon an honor already given.
None could stand before the horde but the Hellwalkers

Obviously just a short one-shot, the muse for this was just floating around randomly. Regardless if you like Halo or Doom better, I've played both and like both (fuck Halo 5 though). Every Master Chief vs. Doomslayer thing I've ever read seems to ignore that they'd be more likely to just go murder hobo on the hordes of enemies both face than to even bother fighting each other. I prefer that, it's far more fun.

Some Infinite spoilers below, you are warned:

The Endless in Halo Infinite were described as worse than the Flood.

I find that to be incredibly stupid.

It would be a cool setup for a crossover like this, though. I can't even say it isn't because Infinite totally fails to tell us anything substantial about the Endless. They're old and can survive the Halo Array and are seen as dangerous by the Forerunners.

No explanation as to any of those, just..given information.

A lot of room for interesting developments, but I am far more concerned about colossal disappointment given 343i and their nonsense in Halo 5.