Opening: Distortion by BABYMETAL

The Doom Slayer rose to his feet, fists raised as he frantically looked around the forest he was in. There was no sign of demons anywhere and that confused him. He didn't ponder any longer as he turned around, observing every nook and cranny of the area but it was simply an ordinary forest, nothing more, nothing less. Still, he was skeptical and the adrenaline flowing through his body would not flush out. He had been fighting for so long it wasn't possible for the adrenaline to go away because the fighting never stopped. However, he does have breathing room to think and consider his current situation. The Dark Lord sent him away to a dimension that is still in-tact, surprising considering any world that has been tainted by Hell's armies would've been burnt to the ground by now. Why would the Slayer be sent to a planet filled to the brim with life?

This was most likely a trap, the Dark Lord wouldn't willingly engage without a plan so there must be a purpose to this dimension, a purpose the Slayer is unaware of. The only thing left to do is spring the trap and see what's in store for the warrior. He found an opening in the forest not too far away and began making his way towards it. He proceeded with caution, still not buying the peaceful dimension he had been sent into as this could be another one of Hell's numerous traps.

He dashed out of the forest expecting a fight but he was greeted by the blinding light of the sun in his eye. His praetor suit immediately filtered the light to make it easier for him to see the vast farmland in front of him. He took in the sight of his new environment and felt nostalgic upon seeing this but couldn't quite place his finger on why. After being woken up by the robotic scientist, Samuel Hayden, in the UAC Facility on Mars, he realized he had amnesia and didn't remember anything from his past besides his unyielding rage towards the demons he despised. Bits of his memory came back over time, or at least, everything he felt he needed to know regarding the likes of the deceitful Maykrs and the ruthless demons.

His attention was drawn to a nearby path that led back into the trees. Following that path was probably his best way to discover the mystery of this dimension and figure out the Dark Lord's plan. As he moved towards the walkway, he reflected on his last encounter with the Marauder. They were comrades, brothers-in-arms at one point in the Slayer's life when they were both Night Sentinels. Time has taken a toll on both individuals and eventually, they found themselves against one another. The Marauder was never a threat to the Slayer but he had proven to be a much more capable foe this time around. The Dark Lord must've played a part in the demon's sudden boost in strength and speed, it was unnatural considering the numerous times they've fought from their initial reunion at the ARC Complex on Earth to the devastated angel world of Urdak.

Once he had arrived at the pathway, he looked both directions and tried to figure out which way he should go. As he looked to the right, he could see a small group of people exit the forest and immerse themselves in the light. Two of them wore similar attire while the third individual had a very grotesque outfit. He didn't pay any more attention to the batch as he set his sights on his next destination. He began walking towards the direction the three boys came from, unintentionally intercepting them.

The member of the group with the most grotesque appearance was shirtless and wearing a boar's head as some sort of mask and he wore a large pelt around his waist as well as having torn his pants in some parts to give his legs the illusion of appearing animalistic. He was taken aback by the Slayer rapidly approaching them, little did he know that he wasn't heading towards them. The boy didn't seem to understand that and unsheathed two serrated blades and leapt towards the warrior while exclaiming, "YOU WANT TO FIGHT?! THEN LET'S GO!" The boy dove towards the warrior, blades first. The Slayer didn't have any business with these children as he quickly grabbed the boar-headed boy and slammed him into the ground as gently as he could without killing him. The boy gasped in pain and breathed as if his lungs suddenly collapsed, letting out the occasional cough as he tried to breathe.

"Inosuke!" One of the boys called out to their dispatched comrade. The other boys that stayed behind were wearing haoris, an article of clothing the warrior was not used to seeing, one was yellow with a triangular pattern and the other had a green and black checkerboard pattern. The one with the yellow haori has loose, yellow hair and screamed at the top of his lungs as he fled back into the forest. The boy with the checkerboard haori had spiky, red-tinted black hair and had a noticeable scar stretching across his forehead as well as a pair of earrings. The boy turned to his comrade who fled and cried his name out, "Zenitsu!" However, it was futile, he was all alone against the incoming green giant. He drew his katana and pointed it at the Slayer while maintaining a firm fighting stance.

As the warrior got closer, the boy was trying his best to focus on his breathing but his skin got slightly pale as if he was terrified and a bead of sweat formed on his head. The Slayer was close now and the boy prepared for a fight as he quickly winced in fear and prepared to block an incoming attack but nothing happened. He opened his eyes and looked behind him to see the green giant had walked past and approached the section of the forest they emerged from. The boy was baffled to say the least as he was expecting a fight but received nothing. He cried out to the warrior, "Wait a minute! Who are you?! Are you a part of the Demon Slayer Corps?!"

The green giant stopped, turning his head towards the boy who froze when the warrior looked back. The boy took a quick sniff and pointed at the armored man, "I'm just guessing because I can smell blood on your armor." The Slayer turned to face the boy as his attention was caught by the boy. The mere mention of the word "demon" got him riled up. However, what also confused the man was that these children are capable of slaying demons. Perhaps killers do come in all shapes and sizes after all. The boy raised his eyebrows in shock as he began to sense the ever growing rage emanating from the man. It wasn't directed towards him, it was a rage for something else. The boy pointed in the other direction as he explained, "If so, we could use your help. We were on our way to investigate a disturbance at Mount Natagumo, that way."

The Slayer knew it, this world wasn't as peaceful as the wildlife made him believe. There was no way the Dark Lord would send him to a world this peaceful, not without a catch. Perfect, that was all the information he needed. The warrior began to pick up the pace and bolt across the area in the opposite direction. The boy followed the man's movement with his eyes and was shocked upon seeing the man's burst of speed but quickly called out, "Wait a minute! Do you even know where Mount Natagumo is?!" The Slayer stopped and looked back, expecting the boy to tell him, "Wait, we'll all go together."

Inosuke slowly picked himself up as he angrily grumbled, "I'll kill him, don't let that bastard near me or I'll murder him!" The boy with the checkerboard haori knelt down to lift his comrade up but Inosuke slapped away Tanjiro's helping hand and tried to stand triumphantly despite the aching pain in his body.

Zenitsu, the one who rushed into the forest in fear, revealed himself as he quietly asked, "Is it safe to come out now, Tanjiro?" The boy assured his comrade that everything was fine and the boys regrouped. The warrior rolled his eyes underneath his helmet in response. These boys were being difficult, just give him the directions and he'll handle the rest. They caught up to the Slayer and began running towards the direction of Mount Natagumo with the warrior begrudgingly following behind.

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Elsewhere, in a dimension very far away from the Slayer and from plain sight is a location unknown to most individuals. The dimension is distorted like an interconnected labyrinth of rooms occupying every corner of the dimension. There were a few open spaces and amongst one of these areas stood a tall and slender man with pale skin and curly, black hair. His pupils are sharp but red unlike his attire which consisted of a black tuxedo with a white tie. He remained in front of a bench covered with scientific utensils and a tray of glass testing tubes. He combined various chemicals together in the hopes of finding the answer to immortality but his train of thought was interrupted once the hairs on his body erected out of nowhere, an event that never happens to the man. Soon, it felt like one of his numerous hearts stopped and he felt a cold chill travel up his body unlike anything he's ever experienced.

He heard the drawn breath of an unknown individual coming from all directions, it was impossible for the man to discern where it was coming from. Soon, a distorted and demonic voice sounded loudly in the man's ears and called out, "It is time for you to play your part, Muzan." Muzan couldn't tell if the sound was coming from his head or not but he angrily lashed out and exclaimed:

"Who are you?! Reveal yourself this instant and I might give you a painless death!"

"You fool.. that is not for you to decide. I shall speak and you shall obey." Muzan chuckled at the statement as he continued shouting:

"Pathetic worm, you cannot speak to me as if I'm some pet. I am Muzan Kibutsuji, progenitor of all demons!" Muzan heard a elegant chuckle in his head before the voice continued:

"If only that were true. Allow me to demonstrate my power."

It happened in an instant, every single pain receptor in Muzan's body flared as he collapsed to the floor, screaming out in pain for the first time in his life. It was a never-ending pain as if something was incinerating his skin on the outside while he was also burning up inside. Every possible pain he could imagine was being stimulated into his body all at once from an unknown source. The demon king rolled around the floor in an attempt to resist the pain but couldn't as he clawed into his hair and ripped it out. His screams echoed across the dimension, he felt he was going to die any second and cried out to the Dark Lord, "Enough! I yield!" The pain went away the minute the demon submitted to his new master. However, he still felt the aching pain and soreness in his body as he was left curled up in a ball on the floor.

"Excellent. With formalities out of the way, I must inform you that the Hellwalker of legend is now in your dimension. Your mission is to finish him by any means necessary, am I understood?"

Muzan lifted his head in surprise as he scrambled to his knees and questioned, "The Hellwalker?! You've got to be kidding me, he's nothing more than a silly urban legend!"

"I do not care for your opinion. I expect results, so start producing them or I will subject you to everlasting pain that will last a millenia. Decide which is more painful for you."

Muzan prepared to argue with the Dark Lord once more but he remembered the excruciating pain he just felt and stopped himself, looking towards the floor in shame as he grumbled underneath his breath, "Yes.. my master…" The intense sensation covering his body faded away and everything returned to normal, he no longer felt the intense pressure weighing his body now as he rose to his feet and angrily slammed his fist into his bench, destroying it. "Damn it all!" he cursed out loud. Never has he been humiliated like this, it was just something that didn't happen to Muzan. HE was to rule everything! Not to be a mere slave to some force of nature he's never met. What's worse, the legend of the Hellwalker turns out to be real and now he has to deal with it. A legend that was created by the people in a futile attempt to instill fear into Muzan has been brought to fruition.

There's no need to worry though, once he has obtained his answer to immortality, nothing will be able to stop him and he will no longer stress about anything else in his life ever again. For now, all he can do is wait until the time is right.