This is a crossover of DOOM and Highschool DxD, I do not own either DOOM or Highschool DxD all rights go to id Software, Bethesda Softworks and Ichiei Ishibumi.

The events in my story take place in an Combined Universe of DOOM (2016) and Highschool DxD some things will diverge from canon and it will manly be set in DOOM's Hell and the Underworld from Highschool DxD.

I am using the Doom Slayer's testament and the lore surrounding it to build this story and basically fleshing out said Testament into a actually story that merges with the background lore from Highschool DxD i.e. the Great War.

There will be no UAC.

This will be a mainly Doom Slayer and Gabriel centric story.

This is just a prologue and I have received permission from Gunkatas to use an aspect of his story in my own.

Prologue:

The Legend of the Doom Slayer

''In the first age, in the first battle, when the shadows first lengthened, one stood. Burned by the embers of Armageddon, his soul blistered by the fires of Hell and tainted beyond ascension, he chose the path of perpetual torment. In his ravenous hatred he found no peace; and with boiling blood he scoured the Umbral Plains seeking vengeance against the dark lords who had wronged him. He wore the crown of the Night Sentinels, and those that tasted the bite of his sword named him... the Doom Slayer''

''Tempered by the fires of Hell, his iron will remained steadfast through the passage that preys upon the weak. For he alone was the Hell Walker, the Unchained Predator, who sought retribution in all quarters, dark and light, fire and ice, in the beginning and the end, and he hunted the slaves of Doom with barbarous cruelty; for he passed through the divide as none but the Three Great Powers had before.''

''And in his conquest against the blackened souls of the doomed, his prowess was shown. In his crusade, the Seraphim bestowed upon him terrible power and speed, and with his might he crushed the obsidian pillars of the Blood Temples. He set forth without pity upon the beasts of the nine circles. Unbreakable, incorruptible, unyielding, the Doom Slayer sought to end the dominion of the dark realm.''

''No aid came from the Devils of the upper layers, for Lucifer fought against his own ruin, besieged and befell by Angel light and dark as the Great War continued like searing fire upon desiccated flesh, alone we stood against the last Human of Argent D'Nur and alone we felt the righteous bloodlust he extrude.''

''The age of his reckoning was uncounted. The scribes carved his name deep in the tablets of Hell across aeons, and each battle etched terror in the hearts of the demons. They knew he would come, as he always had, as he always will, to feast on the blood of the wicked. For he alone could draw strength from his fallen foes, and ever his power grew, swift and unrelenting.''

''None could stand before the horde but the Doom Slayer. Despair spread before him like a plague, striking fear into the shadow-dwellers, driving them to deeper and darker pits. But from the depths of the abyss rose The Great One, a champion mightier than all who had come before. The Titan, of immeasurable power and ferocity. He strode upon the plain and faced the Doom Slayer, and a mighty battle was fought on the desolate plains. The Titan fought with the fury of the countless that had fallen at the Doom Slayer's hand, but there fell the Titan, and in his defeat the shadow horde were routed.''

''And in his terrible rancor between worlds and through time, the Hell Walker found the wretch who shall not be named, but in his heresy was loyal to his evil cause. The wretch adorned the Doom Slayer in a mighty armour, wrought in the forges of Hell, impenetrable and unyielding. With sword and shield of adamantine strength, the Doom Slayer set to banishing all that were left unbroken by his savagery to the void.''

''In his shadow the Seraph would lurk as it had throughout the Great War and even when Devil kin fought amongst themselves for power, the Seraph always the same, watching and guiding but never revealing itself to the Doom Slayer, it's foul presence gave pause to many of Hell's champions, even the Dark Lords remained wary whenever it arrived at the thirteenth layer throughout the ages, though it never remained long, but with each arrival it brought new terrors, bearing terrible gifts for the Hell Walker to wield, the Angel left trails for him to find them, weapons from new ages and those born of Heaven.''

''Yet as the mighty Titan fell and dread engulfed the armies of Doom, the demon priests of the Blood Temples laid a trap to capture this scourge of Hell. Insatiable, even by the vanquishing of the Great One, the Hell Walker sought prey in the tombs of the Blood Keep. And blinded by his fervor, the lure drew him in. The priests brought down the temple upon the Doom Slayer, and in his defeat entombed him in the cursed sarcophagus. The mark of the Doom Slayer was burned upon his crypt, a warning to all of Hell that the terror within must never be freed. There he lies still, and ever more, hidden in silent suffering.''

''For centuries after the entombment of the Hell Walker, the Seraph of Heaven stubborn in it's wretched loyalty to the Doom Slayer still ventured to the 13th Layer, searching; uncaring of the peril that stood against it, it scoured the Umbral Plains and Catacombs of the Damned with ever growing desperation and despair for the crypt in which the Human lay, and with every passage, every temple and every ruin She seeked and every Demon that fell to her blade the closer and closer the slave of Heaven came to reaching the hidden crypt in where the cursed sarcophagus lay, but one day as suddenly as the Angel had came she vanished from the realm of Hell and never returned.''

Relegated to myth in the modern age of Devils and even by many of the other realms, the tale of the Doom Slayer no more than a story from a millennia before the Civil War, an age where the Great War still raged and the Old Devils and Demons still reigned, but still does the image of the Hell Walker haunt the thoughts and dreams of the denizens of the Underworld, his story told from the mouth of parent to the ears of the terrified child, many taking comfort in the pretence that he exists only in the stories they tell.

But.

The horrifying truth is known only to two within all the supernatural realms, one being the current Lucifer of the Four Great Satans; Sirzechs Gremory, the secret passed down from Lucifer to Lucifer, ancient tomes acquired from the sealed 13th layer of Hell; the Old Demon's realm, excavated from the forbidden realm within the Blood Temples of the Kadingir Sanctum.

The other, well; the other being knows the tale better than any other could, she could recount his tale better than any tome could tell, for she had walked with him since the beginning, from a time when he bore not the moniker ''Doom Slayer'' and the many others he earned throughout his crusade against the Dark Lords that wronged him, hidden from him but always guiding as he set forth on his blood drenched path.

She had watched when he fell to his misery for his treachery, she felt his anguish at the loss of his son, with sorrow and pity she guided and watched over him when he plunged himself into Hell where he would become legend, with admiration she gazed at him as he overcome all that Hell befell him, she gave him power when his own failed him, with heartache she cried for him when he lost himself to bloodlust and hatred, his name she remembered when all others forgot, while Hell cursed and scorned him she gazed at him with love.

Gabriel, Seraph of Heaven, she came to care for him; from sorrow and pity, to admiration and love.

She kept him secret from her Father and Siblings, and silently grieved when he was lost to her.

And this;

This is how it all began.

End of Prologue

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First Chapter coming soon.

Next Chapter: The Beginning: The Fall of Argent D'Nur, Birth of the Doom Slayer and Sorrow of a Seraph.