A/N: Hello cyber world and the many that live in it. After some time, I decided to put one last idea into my story pool before throwing myself completely into all of the ones I have posted. My girlfriend had got me into the storyline of RWBY a while back and told me I should consider making a fic about it. And since I'm a fan of RoosterTeeth and Red vs Blue, I decided why not considering all of the hype this series has gotten.

And with the untimely death of the good man known as Monty Oum, I feel the need to offer my own story in his memory. I just hope that I can make this something that he himself would have considered good reading. So in his memory, I offer you the first ever DOOM/RWBY crossover!

I own neither franchise.

("The Devil is real...I know, I built his cage." -UAC Scientist before his death.)

Personnel Dossier:

Name: Johnathan Grim

Alias: 'Reaper'

Age: 17

Height: 6' 0''

Weight: 157 lbs.

Eye Color: Blue/Green

Blood Type: O-

Occupation: United Space Marine Corps - Private First Class

Qualifications:

- Above Average skill in Assault.

- Above Average skill in Survival training.

- Above Average skill in CQC

- Average skill in explosives.

- Average skill in engineering.

Notes from Superior:

Despite his young age, PFC Grim has shown to have a skillset on par with soldiers years ahead of him.

Being an orphan, he handed in transcripts with a faked age in order to gain entry into the USMC. Something that had been overlooked until his training was completed and his birth records had been located.

However, instead of punishment and imprisonment. Those that trained him admitted to seeing something in Grim that was rarely found in other recruits, and all of them agreed to have him serve instead of sending him off and all the training he received to go to waste.

Grim has also shown an unbreakable will in the face of overwhelming odds. Even when the marines began beating and hazing the young PFC he refused to give in and fought back. His records indicate multiple trips to the infirmary, but not once did he reveal the names of his attackers. It was believed that he was proving to those older than himself that he was just as strong as they were.

He was given his nickname, due to an incident that occurred in the last month of his training. Three older marines had gotten intoxicated and attempted to kill Grim when he was on his way back from the mess hall. The resulting fight that took place ended with the three men being killed and the PFC only suffering minor injuries. Once footage of the altercation was revealed, the incident was labeled as Self-Defense and Grim was cleared of any charges.

Since then, he has been referred to as 'Reaper' by fellow recruits and superiors alike.

Given the current situation regarding his age, the Commanding Officials refused to send him on missions that would have bad feedback from either the government or the public. But recent events have managed to allow him on a handful of assignments that were completed without fail.

PFC Grim is due to be shipped out on his first solo assignment, as an addition to security detail on one of the UAC's biggest research facilities where they are in need for helping hands. The lead official, Sargeant Alexander Kelly, requested Grim after reading his file and said that; 'An important assignment for the kid will be good for him. Too much talent to be wasted otherwise.'.

The assignment was cleared as of this past November and Grim is to be transfired to the UAC Facility located on Mars by the end of this month. Given his record, he should be a useful asset to both the security forces and the UAC all together.

X

John's eyes snapped open when the dropship docked at Mars City. Running a hand over his shaved scalp and suppressing a yawn, he picked up his rucksack before heading toward the hatch as it opened allowing the occupants off.

The two men that had been riding in the shuttle with him, a bald man in a black suit and his guard who wore the standard USMC armor just like he was currently, stepped off first and made their way to administration area.

"I can't believe it's come to this. I didn't want to come here." said the suit.

"He left you no choice." said the guard.

"True. But this is the last time." relented the suit, "I'm tired of running damage control every time he makes a mess."

His escort nodded, "Right, you're the control. And if all else fails, I'm the damage."

"If that's what it takes, Betruger is going to do things our way." added the suit as they vanished through the doors ahead.

John shook his head, wondering what that all had been about before he was approached by one of the security guards stationed in the docking area. "Welcome to Mars. All new arrivals need to get checked in at reception." he said pointing toward another door way off to the side.

Nodding, John made his way up the flight of steps leading out while the dropship took off. Entering a checkpoint area where a pair of scanners were set up infront of reinforced glass with another guard sitting at a terminal.

"Welcome to Mars, marine." said the guard punching in a few keys. "I'm gonna need you to step on one of those red squares on the floor for a bio-scan. This should only take a second or two."

The young marine stepped in the middle of one of the squares and waited. The scanner coming to life moments later as a red beam rose up and down over his body a few times before hovering above him and spinning a few times. He'd been through these scans back on Earth and remained perfectly still so that they could get an accurate reading.

A small screen on the scanner showed his skeleton and biological information as the device finished its task. "Alright, bio-scan looks good. You're clear for entry." said the guard as the door beside him slid open allowning him to move on.

Stepping through an open room , side stepping a spider-like sentry bot that scuttled past and went into standby mode on the platform beside another door. John turned back to face front as he went through another door and approached the reception desk.

"Welcome to Mars, first time?" asked the man behind the desk.

"Yeah, just got in." replied the marine dropping his bag beside the desk. "I was reassigned as part of the security personnel out here."

The man nodded and began typing at his terminal. "Alright, just leave your bag there, I'll have it sent up to your quarters." he reached down behind the desk and pulled out a handheld device. "We just have to take care of a few things first. This is your Personal Data Assistant, you'll need it to access all secure areas. Standard for all marines stationed here. If you get any new clearence codes for whatever reason they'll download directly."

He went back to the computer and typed a few things, "I see here that you're to report to Sgt. Kelly at Marine Command immediately. It's just that way, follow the signs." he said pointing to the hallway on the right.

Nodding to the administratior, John made his way through the corridors past the various personnel that were either working or passing through. Coming into an open space where he saw the two who had been on the ship with him before in a small conference room talking with an older man wearing a doctor's outfit, left eye a cold grey color while the other was milky white with several scars marring the side of his face around it.

"I'm here, because there seems to be serious problems." said the suit leaning on the center table.

"Oh really?" asked the doctor. "Do I need to remind you of the groundbreaking work that we're doing here?"

"No." said the other man shaking his head. "But I've been authorized by the board to look at everything."

The doctor smirked condescendingly. "The Board authorized you? Hmm. The board doesn't know the first thing about science. All they want is something to make them more money. Some product. Don't worry, they'll get their product."

"After how many accidents? Tell me Doctor Betruger why are so many workers spooked, complaining, requesting transfers off Mars?" asked the suit.

Betruger seemed unaffected, "They simply can't handle life here. They're exhausted and overworked. If I had a more competent staff and bigger budget, even these few accidents could have been avoided."

"I'm afraid you'll get nothing more until my report is filed with the board." said the other man while his guard looked out the window and caught John's gaze as he stood there listening. "I'll need full access, Doctor Betruger, Delta Labs included. I won't have any difficulty doing that will I?"

"Only if you get lost, Swan." the doctor replied calmly. "Just stay out of my way. Amazing things are going to happen here soon, you just wait." with that he disappeared through the door on the opposite end of the room.

Swan narrowed his eyes after him before turning to his escort, "Lets go."

John couldn't make heads or tails about what he had witnessed. But something about the one eyed doctor put him on edge. Something about the look in his gaze made him feel on edge for some reason.

Seeing the time, he started moving again in the direction of Marine Command. With every step, a odd feeling of unease continued to settle deep within his being. Like an instinct warning him that something bad was going to happen and soon. It was one he had, had a few times in the past, one that had saved him more than once on several occasions.

Shrugging it off, John took a deep breath and prepared to be nothing more than a security guard for a bunch of jumpy egg-heads on a desolate world.

"This is going to be Hell." he thought bitterly as he continued on his way...

...

...He had no idea of the events they that would take place that would end up proving his thoughts right.

X AN UNKNOWN NUMBER OF DAYS LATER X

John slammed a fresh clip into his machine gun before firing a volley of slugs into an Imp that crawled its way out of the swirling vortex of flames and dark energy that was in the center of the room.

Blood and sweat pouring down his face, stinging his eyes as the heat in the massive chamber beneath the surface of Mars rose steadily. More creatures came pouring out of the vortex and attacked him only to be cut down and reduced to piles of desolving ashes.

But they weren't the real threat. That belonged to the 30 foot tall beast that was currently stomping in his direction. It's body a horrifying combination of flesh and machine, its entire right forearm a massive rocket launcher that would obliterate him in an instant if a round managed to hit its target.

Towering over him, the beast let loose a bellowing roar that shook the very chamber. Fire billowing out of its mouth and drifting past its large set of horns. The cannon that was its arm began glowing as it aimed at the young marine.

John gritted his teeth and threw himself aside, rolling as far out of the way as possible as the ground beneath him shook. Chunks of flaming rock pelting over his form as he dragged himself back to his feet. None of the weapons he had collected since this nightmare began would have any effect on this thing, it was just too powerful. His only hope was to use the artifact he found within the barriers of Hell itself to take it down and seal the portal before the fleets arrived.

Switching to his double barrel shotgun, he blasted one of the two headed demons, a Maggot, in half. Counting five in his head just as he heard a multitude of voices whisper at once. "USE US."

Shouldering the shotgun, John reached into his scratched, burnt and dented armor. Pulling out a cube-shaped artifact that had five glowing lights on the surface with a face-like image in the center facing him. The artifact, the Soulcube, hovered in the air before his outstretched hand, a series of gold-colored blades sprouting from its frame and spinning around it while it waited to be used.

When the beast turned, aiming its cannon at the marine, John cocked his arm back and threw the Soulcube with all his strength. The artifact shot through the air straight at the large demon and struck, its blades slicing clean through the monster's hide causing gallons of blood to spray forth from the wound it had made.

Roaring in agony, the demon's cannon went wide and blasted a section of wall instead of its intended target. The chamber shook from the blast, causing chunks of rock to rain down from above.

Catching the Soulcube when it came back, John was knocked to the ground when he was tackled from behind. The screech of the Imp that got the drop on him almost deafening him as it attempted to claw through the backpack he was wearing and the armor underneath.

Thinking fast, he rolled hard to the left. Slamming the Imp hard into a large rock close to the portal, disloging it from his back and rolling the other way back to his feet. Pulling out his sidearm and shooting the demon twice in the head and killing it. "One down, four more to go." he said to himself before looking up and seeing the beast looking down at him.

A rumbling growl of primal rage emtting from it as it raised one of its massive hooves. "SHIT!" the young marine shouted as he threw himself back as the demon's limb slammed into the ground where he had been a moment before. Reaching back and pulling out his plasma rifle, he let loose a stream of blue plasma bolts at the creature. Each hit doing almost nothing to it as it started stomping after him.

"Guess this thing isn't called Hell's Mightest Warrior for nothing." the marine thought as he started running. Shooting two lesser demons with his plasma rifle before dumping the spent energy cell and injecting a new one.

"WE MUST HURRY." spoke the Soulcube. "THE PORTAL NEEDS TO BE SEALED, OR ALL WILL BE LOST."

"I'm trying!" John roared back in his thoughts as he killed another lesser demon. Dodging another rocket blast from the beast chasing him. "Is there another way to kill this thing AND stop Hell from being unleashed?!"

The artifact said nothing as he pulled out the double barrel, cracking the breach open and dumping the spent shells before slamming in new ones and snapping the weapon closed. Another Maggot crawled out of the portal and shambled his way and he took aim, finger tight on the trigger.

An explosion from closeby threw his aim off and he missed, the blast also sending him airborne. His body crashing to the ground and slamming into the wall of the ruins he had come through on the way in. The path blocked when the archway collapsed after the fight first started.

Groaning, John dragged himself along the ground until he managed to get to his knees and push himself to his feet. Picking up the dropped shotgun as he faced his opposition.

Over two dozen demons; Imps, Maggots, Pinkeys, Lost Souls, and a couple others stood facing him. And behind their ranks stood the larger creature. Hell's mightest warrior, the Cyberdemon. Arm cannon primed and ready to end the marine's life where he stood.

His body ached, exhaustion slipping into his bones like a virus. He'd been fighting non-stop for days, fighting for not only his survival, but the survival of humanity since he was the only living being not from Hell that was still alive. The only one capable of ending the nightmare before it plagued the Earth.

And now there was no way out. He was going to die here with the odds so heavily staked against him. And if he fell...so would the rest of his race.

"THERE IS A WAY." whispered the Soulcube in his mind. "A WAY TO STOP HELL'S ARMIES AND SAVE YOUR PEOPLE FROM EXTINCTION. BUT THE PRICE WILL BE GREAT."

John kept his eyes locked on the demons as they started to close in on him, preparing for the kill. "What do I need to do?" he thought seriously.

The sentient artifact hummed to life within the compartment where it was stored in his armor. "INSTEAD OF FEEDING US ONE FINAL SOUL FROM THE HORDE, THROW YOURSELF INTO THE PORTAL. OUR POWER WILL BE ABLE TO USE YOUR SOUL TO NOT ONLY SEAL HELL'S OPENING, BUT WILL COLLAPSE THESE RUINS ALONG WITH THE STRUCTURES ABOVE. NOTHING WILL SURVIVE."

The young marine breathed deeply. He would have to sacrifice his life and soul in order to stop the portal and whatever came through it. He was still going to die deep within Mars...but at least he would be able to do it on his terms. And he'd be taking all of these beasts with him.

"Whatever it takes...these bastards cannot reach Earth. If I have to give up my life to do it...then I'll do it." John thought back with conviction as he raised his double-barrel at the horde before him. The creatures all roared in response before charging toward him.

Roaring a battle-cry of his own, the young marine met their charge head on. Blasting both barrels of the shotgun and critically wounding one of the Pinkeys, giving him an opening as he barreled through their ranks. Dodging claws and other deadly limbs as he broke through them.

The Cyberdemon roared as it fired down at the ground, but John had expected it.

Dropping low, he slid across the rough, heated ground between the larger demon's legs as the explosion wiped out the lesser creatures that couldn't get out of the way in time.

Getting up, John looked down into the vortex of fire and energy below. Steeling himself as he put his gun away and took out the Soulcube, clutching it tightly in his hands before turning back and glaring at the Cyberdemon. The beast priming its arm cannon for another blast while he stood at the edge.

The marine raised his hand and flipped the large demon the middle finger. "I'll see you in hell, motherfucker!" he shouted before throwing himself over the edge. The portal below swallowing him up the moment he made contact with it.

All around him, John saw the endless tunnel of flesh, blood and fire much like the last time he had gone through a portal to the devil's domain. The Soulcube hummed loudly in his hands, a glowing light beginning to emit from it that surrounded his entire body.

Despite his imminent demise, a sense of peace began to flow through him. Throughout everything he had endured, survived and fought, it would all finally be over. Hell's army would fail. The blood thrusty monsters that were the cause of the deaths of everyone within Mars City would be stopped by a lone human as young as him.

It was almost poetic...and a big middle finger to Betruger for everything he had done to cause all of this. Hopefully that bastard was roasting in the very pit he tried to unleash for what he had done.

The light that covered his body became blinding, and John was starting to feel light headed as he closed his eyes. The pain from his numerous injuries, new and old, faded away as he slipped into blissful oblivion.

An explosion of pure energy burst forth from the artifact. The portal shook from the intensity before it started to collapse in on itself. The sudden burst had been so powerful that it burst was so powerful that it shot from the vortex and struck the ceiling of the chamber that housed it. The walls shuttering and cracking visiously before it started to cave in, the ground above splintering and falling into the massive hole that was opening within Mars' surface.

The fires from the portal itseld started dying, the flesh that made up the interior began to harden to stone and close up as the chamber fell down on top of it. Killing what creatures that may have left its confines and sealing it forever.

When Earth's fleets arrived almost an hour later, all that they found of the large UAC facility was a massive crater. All of the buildings and towers nothing more than rubble lost below the surface of the red planet like a title wave.

They would spend weeks combing through the wreckage, trying to discover anything that would lead to what happened and what was going on up there. But they would find nothing, and the UAC would simply call it a horrible disaster that caused the loss of good people and resources. The possibility of rebuilding sometime long down the road after the families of those lost had time to mourn.

None of them knew of how close they had become to extinction due to a corrupted scientist's ambitions. And the sacrifice of a lone marine that saved them all. His courage and stength never known, but the lives of every man, woman and child had ment more to him than anything when faced with the ultimate choice.

By sealing Hell's portal, he saved Earth at the cost of his own life. An unsung hero, but a hero none the less given his actions.

And as the old saying goes...not even death can keep a true hero from his duty. And Hell's influence was far from over.

XXX

He felt as though he were floating through warm water. His body weightless as it drifted through the abyss, no pain, no monsters, nothing but peace as he drifted through where ever he was. Time not being relevent as he was finally able to ease his mind from the horrors and nightmares he had come face to face with.

As he floated in the abyss, he heard whispering coming from all directions. But he couldnt' see where they were coming from.

Was he dead? Was this purgatory where a higher power would decide where his soul would go for all eternity? He'd seen Hell in person, so there must have been a Heaven. Maybe he would get lucky enough to see it as well.

All the voices stopped. Plunging him into silence once more as though they had heard his thoughts. "NOT YET." spoke an array of tones as one before everything was bathed in a flash of bright light.

XXX

The weightless feeling slowly started to fade away as his senses began to come back to him. John slowly opened his eyes, the blaring light forcing him to close them as he tried to regain himself.

His body felt numb, but as the seconds passed he was able to feel grass beneath him. When he opened his eyes again, we was able to adjust much easier as he looked toward the bright-blue sky above him along with the tops of several trees that surrounded him.

This...wasn't what he was expecting. Slowly sitting up, his body aching slightly as he looked around him to see the lush forest that he had woken up in.

It was quiet, peaceful. The forest surrounded the small clearing he was in casting shadows on the tall grass from the sun hanging high in the sky above.

"Where am I?" he wondered outloud. Racking his brain as he tried to figure out how he had gotten here. He remembered the final battle against the Cyberdemon, throwing himself into the portal with the Soulcube using his own soul to fuel its power...then nothing.

"Is this the afterlife?" he thought to himself while looking around again. Turning his gaze down at himself he found his armor and clothes still damaged from the many fights he had been through, but his injuries had been healed and scarred over.

Taking a few moments to gather his wits, John looked to his right and found his backpack along with his weapons scattered on the ground. Getting to his feet, he shambled over to the pack and started checking over his supplies. His weapons were all still in one piece thankfully, along with his ammo and what little medical supplies he had left.

"Guess I'm not dead, if I still have my weapons with me. But where the hell did the Soulcube take me? Am I back on Earth?" he said outloud after loading fresh shells into the double-barrel shotgun he had picked up in Sgt. Kelly's office back on Mars.

Slipping it into his pack and slipping it on before taking out his PDA and began checking it. A few small cracks were on the screen along with a couple of deep scratches, but it was still fully functional. Though it didn't provide much help since it couldn't pick up a signal from any of the UAC instillations for some strange reason.

Putting the device away, John took out his machine gun and looked around at the forest again. "I'm not going to get any help just standing here. Better try and find civilization and link up with any marine regiment that could be close by."

Weapon held tightly in hand, eyes naturally scanning for threats, the young marine headed into the forest in the direction he knew to be North. "At least there aren't any demons or other abominations trying to tear me apart." he couldn't help but think as he made his way through the trees.

Unknown to him, several sets of glowing red eyes watched him from the shadows. Low growls coming from the dark forms as they slowly started to stalk after the marine.

XXX

Elsewhere, a familiar ancient artifact laid in a small crater that had been burned into the ground where it had landed. The amount of power it had unleashed forcing it into a dormant state as it began recharging itself.

Footsteps could be heard drawing closer to it until a shadow cast over the artifact. "Whoa...what's this thing?" asked a girl's voice as they knelt down beside it.

The girl was young, roughly 15 years of age with black/red hair cut short wearing a black and red corset, skirt tights and boots. A long flowing red cloak billowing behind her and a massive hybridized weapon resembling a scythe and a sniper rifle in he hands.

Reaching a pale hand out, she touched the warmed surface of the artifact. Running her fingers over the strange designs etched into the surface before picking it up and looking it over closely. "It's kinda cool." said the girl smiling as she rolled the thing over in her hands.

"Ruby?! Where the hell are you?!" called another girls voice making her jump and almost drop the thing she found.

"Coming Weiss!" she called back as she took the artifact and slipped it into a pouch on her belt and running to catch up with her new partner.

The Soulcube glowed briefly from its new spot for a moment before going dark again. "THIS ONE IS PURE...WE ARE SAFE." he whispered softly.

Ruby Rose froze mid-step, "Hello? Is someone there?" she asked looking for the source of the strange voice she had heard and finding no one around. Shrugging, she jogged toward where Weiss was waiting so they could finish their initiation.

A/N: A slow start, but one worth giving a great deal of effort. For those that haven't played DOOM, this story is based in the third game along with the content for it and the download content for it. And with this being a RWBY fic, you know things are going to get intense later down the road.

Tell me what you think guys. I got a lot of food on my plate, but I can manage with everything. So no worries.