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, and those that tasted the bite of his sword named him... the Doom Slayer.

-Slayer's Testament I

Naruto was floating down the river in the Valley of The End. Sasuke had put his Chidori through his chest. Now he was dying and drowning while Sasuke was being carried away by an all too late Kakashi. Kakashi arrived after Naruto had floated downstream. He looked around to see only an unconscious Sasuke "I'm too late," Kakashi murmured as he fell to his knees, "I failed you sensei... I failed you, Naruto," he said as he looked at Sasuke. Picking up the boy, he slowly stood up as Pakkun appeared at his side, "I'm sorry Kakashi, but I can't find the kid anywhere," Pakkun said

"He's gone, I knew that the moment I arrived... I failed," Kakashi said as he turned around to talk back to Konoha, "let's go, Pakkun... I-I've seen enough for one day,"

"If you say so," Pakkun replied as they went back to Konoha.

With Naruto:

Naruto had his eyes closed as he waited for the embrace of death. But inside, the Kyubi was anxious to get out, "Finally, the brat's dead, now I can get out of here," the Kyubi said with a smile, "stupid Yondaime, thinking he could seal me away. You know what, I think I'm going to destroy the last bit of the seal just to rub it in his face," he continued as he reached for the seal on the gate. He went to drag his claw across the seal, but when it did touch, it glowed red and the Kyubi recoiled at the pain it felt, "GAH! What was that?!" the Kyubi shouted as a voice spoke out

"When the blood of the mother stops, the blood of the father starts. Let the ghost know that he is to wear the crown of the Night Sentinels and do as his predecessor continues... Let the son rip and tear!" the voice echoed as the Kyubi thought out loud for a few seconds

"Night Sentinels? Where have I heard that before?" the Kyubi asked himself when he saw smoke and a hell-ish glow at the other end of the sewer that was Naruto's mind. The Kyubi squinted as he looked out past the bars of his cage. A figure soon started to approach wearing green-armor and a double-barrel shotgun in his hand.

The Kyuubi's eyes widened as the man approached with silent anger. He was soon in front of the cage as he put the shotgun on his back and placed his hands between the bars. The man then pushed the bars apart, opening the cage as the Kyubi backed away in fear "N-NO! I-It can't be!" the Kyubi cowered as the man approached him. The Kyubi continued to shake in fear as he grew ever closer "S-STAY AWAY FROM ME!" the Kyubi shouted as he swung his arm, sweeping the man away. Running out of the cage, the Kyubi ran down the sewer as fast as he could, running away from the man. But he soon felt something climbing up his arm as he looked down to see the man grabbing his fur and climbing up toward his head. The Kyubi went to swat the man as the ladder jumped onto the former's hand. The man jumped off the Kyubi's hand and landed on his snout. The man aimed his shotgun at the Kyubi's eye and pulled the trigger. The Kyubi shouted in pain as he fell to the ground and clutched his missing eye. The man stood in front of the Kyubi as he cracked his knuckles, "P-please, s-spare m-me, S-Slayer," the Kyubi begged as the 'Slayer' only punched him in the nose

"GAH!" the Kyubi shrieked as his mouth opened. The Slayer then grabbed one of the Kyubi's teeth and pulled it out, causing the giant fox to scream even more. Grabbing the foxes tongue, the Slayer stabbed the tooth through the tongue and stomped on it, almost 'stapling' the Kyubi's tongue to his bottom jaw. But before the armor-wearing man could continue, someone caught his eye as he looked over to see a boy floating in the water. The man slowly walked to the boy as he knelt down and picked him up in his arms. Walking back to the Kyubi, the man set him down in front of the fox as he pointed at him and then the fox "Y-ya wa m-meh t-ta hea hi?" the Kyubi asked as best he could, his own tooth preventing him from speaking properly. The man nodded as the Kyubi quickly used his own chakra to start healing Naruto. As the boys' injuries started to heal, a man with purple skin, horns, and a knife in his mouth appeared.

"I have come for the soul of the child," he said as he looked at what was going on. The Kyubi was healing Naruto as the Slayer was pointing a shotgun at the Kyubi, who was currently missing an eye and had a mouth full of blood, "O-oh dear," he said as the Slayer turned around to look at him, "h-hello, S-Slayer," he stated as the Slayer continued to flip him off. The Shinigami gulped as the Slayer lowered his hand and looked down at Naruto, who was healed... well, Spiritually anyway. Putting his shotgun on his back, the slayer picked up Naruto and started to walk toward the Shinigami. The Shinigami was currently shaking in fear as he approached, but the Slayer turned around and pulled out a small stone tablet. Crushing it in his hand, the same echoey voice spoke: "Preserve the body of the son so that he may return on the 3rd year for the battle against demons and their kin.". The Kyubi quickly nodded as the Slayer turned to the Shinigami and pointed at his stomach, "W-what are you doing?" the Shinigami asked as the slayer continued to point at the death god's stomach, "Y-You don't want to go in there, it's hell... wai-oh... oh, f-forgive my stupidity, Slayer! I-I'll take you straight to hell right away!" he stated as the Slayer shook his head. Holding up Naruto to Shinigami, the ladder took hold of him as the Slayer took a step back... and faded away. The Shinigami looked down at Naruto and at the spot where the Slayer stood, "You were supposed to go to heaven boy, yet your father wishes you to fight alongside him... I hate my job," the Shinigami said as he then looked at the Kyubi, "do as the Slayer says and make sure nothing more happens to the boy's body. We don't want to upset him more than he is now,"

"Y-ye, ir," the Kyubi replied as the Shinigami sighed

"I'm sorry, Naruto, but I cannot deny the Slayer, even the demons need to know peace after their massacre by him," the Shinigami said as he opened a portal. Going through it, the Shinigami looked around to see that they were at the Hell Bridge.

Looking around, on the ground was a pistol next to a corpse with a note stabbed into the back. Setting Naruto down next to the corpse, the Shinigami hit himself as he said: "What am I doing with my life?" as he left, but not before giving Naruto some armor.

'It's an older model, but it'll work for now,' he thought as Naruto laid there next to a corpse and the armor.

[Sorry if this first chapter was kinda bad, I haven't played DOOM since last year and I'm gonna need a bit of research. Also, special thanks to @user92082673 for suggesting this idea and hope you liked it especially]