Within the Dimensional Infinity Fortress, a certain demon had decimated an entire army of demon slayers. His grotesque form, adorned with several mouths and sharp fangs across his arms and legs, was drenched in the blood of humans. The macabre display only fueled his appetite, hastening his recovery.
Plum-red eyes, narrow like a cat's, surveyed the carnage around him. His long white hair cascaded down his back in an unruly tangle, contrasting sharply with the dark crimson marks that branched haphazardly across his limbs and body.
Most of his subordinates had been defeated, but one remained: Nakime, an Upper Moon demon whose Blood Demon Art had taken form as the entire fortress. However, even that formidable structure was on the brink of collapse.
As he made his way towards the outside world, where the humans prayed for the sun to eventually destroy him, his last subordinate cast a Blood Demon Art upon him. A swirl of blackish crimson miasma enveloped him, and he felt himself being transported into another world.
The demon's eyes widened in surprise and confusion as he emerged from the swirling vortex. This was not the world he knew, his senses bombarded by a cacophony of sounds and sights unlike anything he had ever experienced before. The towering structures of steel and neon stretched towards the sky, casting an eerie glow over the bustling streets below. People, with their strange clothes and metallic limbs, moved about in a blur of motion, their faces twisted into masks of determination or fear.
He took a tentative step forward, his claws scraping against the cold, hard pavement. He was fascinated and repulsed in equal measure by this new world. The scents that wafted towards him were foreign and artificial, and the demon could sense the fear and anxiety pulsing through the humans around him as they glanced his way.
His eyes glinted with a mix of curiosity and hunger as he surveyed the scene around him. He was far from home, in a world that was both wondrous and dangerous.
The demon approached a group of humans huddled together; their eyes filled with terror as they watched him approach. He could hear their frantic heartbeats, smell the sweat and fear emanating from their bodies. They had no idea what was about to happen to them.
He stepped closer to the trembling humans, his eyes glowing with a malevolent light. With an expressionless face, he arms sudden elongated into a long whip with irregular blades of bones and teeth protruding around it, grazing the humans in a blink of an eye.
"You will soon become like me, immortal and powerful beyond your wildest dreams," he spoke to them.
The transformation began immediately. The humans' bodies writhed in agony as their bones shifted and elongated, their flesh bulging and twisting into new shapes. Their screams filled the air, but the demon took no notice. This was the price of power, and he held no emotional attachment to the pain he inflicted.
As the transformation neared completion, the demon's newest set of spawns rose to their feet, their eyes now glowing like their master's. Their body were a twisted parody of what they once were, monstrous creatures with razor-sharp claws and fangs dripping with saliva. They looked upon the humans with newfound hunger and lust, eager to sink their teeth into their flesh.
The demon continued his work, injecting more and more humans with his blood. Their transformations were just as agonizing, just as violent. Some didn't survive the process, their bodies torn apart from the inside out. But for those who did, a new life awaited them, a life of power and immortality under the demon's rule.
The demon reveled in the chaos he had wrought. He watched as his new minions tore into the remaining humans, their screams of terror music to his ears. He would gradually learn more about this world and then create a new order, a new world, one where he and his kind would reign supreme. And nothing would stand in their way.
The demon king, Muzan Kibutsuji, stood atop a skyscraper, overlooking the sprawling city of Nexus. In just a few days, his army of demons had spread like a virus, preying on unsuspecting humans under the cover of night. The Nexus Police Station was on high alert, and the officers were ill-equipped to handle the demonic threat. Some had already fallen to the demons' rapid regeneration, while others had barely escaped with their lives.
As Muzan surveyed the city, he accessed and utilized the internet, absorbing a wealth of information about this new world. He was both fascinated and terrified by the technological advances of this place, which were centuries ahead of where he came from. While there were no meddlesome demon slayers, the sun wasn't the only threat that he had to worry about because the human race had been riding on the exponential rise of technology for so long that the delicate balance of the entire world depended on the principle of mutual assure destruction. Muzan's desire for eternity was threatened by this world, for even an immortal being like him could be destroyed by the powerful military arsenal at humanity's disposal.
He knew that if he was to succeed in his quest for true eternity, he must eliminate anything that posed a threat to his existence. Humans may be weak and frail, but their collective intelligence and technological prowess surpassed even his own vast knowledge and wisdom from a thousand years of living.
With this in mind, Muzan continued to inject more humans with his own blood, transforming them into demons like himself. The transformation process was excruciatingly painful, and the newly turned demons writhed in agony as their bodies mutated at an alarming rate. But the end result was worth the pain, for they emerged stronger, faster, and almost invincible. His army of obedient demons would continue to grow.
However, Muzan's body convulsed with violent spasms, his hands clutching at his chest as he coughed up thick, viscous blood. His skin, once taut and smooth, now appeared to be withering and wrinkling before his very eyes.
The reason had to be that woman. I'll bring back Tamayo's cells that I absorbed.
The demon king would bring back Tamayo's cells that he had absorbed deep within his body. He concentrated his thoughts, gathering the cells in one spot and focusing his willpower to communicate with Tamayo's consciousness directly.
"What did you do to me? Wasn't the medicine you used on me supposed to turn me human?" Muzan demanded of her, the anger and frustration evident in his voice. He had been tricked by the demon doctor, lured into absorbing her with came along with a cure that would revert him back to his human form. But he had long since neutralized that cure, and now he was paying the price.
"The drug… I used… turns you into a human… and…," Tamayo spoke in a docile tone before her words trailed off, and she gave a vicious grin, revealing her fangs as she glared at him with demonic eyes. "I'm not telling you. Why don't you try using all those useless brain cells you now have?"
Enraged beyond measure, Muzan crushed her cells with a furious wave of his hand, scattering them once more.
I'll look through the memories left in her cells.
And through those memories, he saw the Insect Hashira.
This woman is a human… the poison user who was eaten by Douma.
The short young woman was collaborating with Tamayo as they devised a drug together.
"Let's try creating a hybrid drug. We should proceed forward based on the presumption that the drug will decompose. The first effect should be turning him back into human. And if that doesn't work, we should create something with the remaining drug that will have a stronger effect."
"An aging drug is idea for the second effect. If we use what you created, Tamayo-san, then we can age Muzan by fifty years per minute."
Muzan widened his eyes.
Aging! I see. So, I've been continuously aging. My power was being chipped away to stave off the aging progression. Tamayo used the drug on me a few days ago. About seventy hours… which means that I have aged by over 200,000 years!
I should've realized it earlier; the color of my hair wasn't changing back.
For as long as Muzan could remember, he had never experienced fatigue as a demon. But regeneration consumed energy, and by relentlessly fighting against Tamayo's aging drug, his body had been drastically weakened. He needed time to neutralize this drug.
But as the demon king kept a low profile to buy himself time, one of his subordinates had spotted a certain kimono-wearing demon wandering towards the edge of the city.
Kamado Nezuko is here too? Excellent work, Nakime. By bringing her to into this world, I can absorb her and conquer the sun.
He summoned one of his demons and gave out an order, "There's a demon who escaped my control. She was last seen heading towards the outskirt of the city. Find her and use your Blood Demon Art on her. She is a girl in a leaf-patterned, linen kimono and a checkered sash."
The demon was dispatched on a specially assigned mission. His skin had a sickly gray hue, pulled tight over his bones, revealing the pulsing black veins just beneath the surface. Strands of long, jet-black hair hung in tangled strands around his face. His mouth was filled with razor-sharp teeth that glimmered in the dim light, while his eyes blazed with a sinister red hue that seemed to pierce through the darkness.
Under the cover of night, the demon searched for Nezuko, hunting her down through rain and thunder. But fate had other plans, and the demon found himself face-to-face with an unexpected adversary: an adolescent boy armed with a concealed electric blade. The demon saw the boy as just another human to be consumed, but the boy fought back with unrelenting fury, showing no mercy to his demonic foe.
After being ran over by an accelerating vehicle, the demon's splattered body was later transported into an underground laboratory, cryogenically frozen within a tube.
"Ugh…," the demon's eyes slowly fluttered open, the darkness of his frozen slumber dissipating into the brightness of the present. The first thing he felt was an intense coldness, a bone-deep chill that permeated his entire being. His body was stiff and unyielding, like it had been turned into a block of ice. Every movement sent a searing pain through his limbs, as if the very act of bending his joints would cause them to snap in half.
As his eyes adjusted to the light, he saw a red-haired woman standing over him, her hand holding up a flashlight.
"You must be feeling awfully cold. Allow me to warm you up," Dr. Nova's voice was laced with a sadistic glee as she spoke, a hint of malice lurking just beneath the surface.
Before he could even react, she flipped a switch on the flashlight, and the light grew even brighter, burning into his skin like a white-hot flame. "Arugh!" The demon let out a guttural scream, his body convulsing as the heat overwhelmed him. Black smoke began to radiate out from his skin, a sizzling sound filling the air as his flesh started to char and burn. The pain was unbearable, and the demon felt like he was going to burst into flames at any moment. He tried to cry out, but his voice was choked off by the agony wracking his body. All he could do was writhe in pain as the sadistic doctor continued to torture him, relishing in his suffering.
The woman's eyes sparkled with fascination as she examined the results of the experiment. The demon writhed and squirmed in agony under the white-hot beam of light, his skin blistering and blackening with each passing moment. "Nezuko was right," she mused, "you really are weak to sunlight." She turned to her two spectators, a grin spreading across her face.
Ijin and Nezuko stood on the other side of the room, watching in awe as the scene unfolded before them. It was Ijin's first time witnessing the power of artificial sunlight, and he was spellbound by the display. Meanwhile, Nezuko couldn't help but be amazed by the small device's ability to contain the blazing heat of the sun. She couldn't believe that such a useful tool existed.
"How is that possible?" she asked openly. Demon Slayers had to undergo grueling, harsh to hone their skills with their special swords. If they had such a useful tool that shined sunlight, they would have been a huge game changer in their fights against demons.
Dr. Nova turned off the flashlight, allowing the charred demon the slowly regenerate. "This is a solar simulator," she explained, her voice low and even. "It reproduces the properties of natural sunlight. Normally, it's used to test photosensitive materials, but for our purposes, we used it on a live specimen. For the sake of portability, I embedded it into a flashlight."
Nezuko and Ijin listened intently as Dr. Nova continued to explain the science behind the cruel experiment.
"We can view sunlight as merely a spectrum of electromagnetic radiation composed of ultraviolet light, visible Light, and infrared Light. Obviously, visible light isn't the culprit here; otherwise, this demon would be burnt to ash from just any ordinary light. By crosses of elimination, it's really ultraviolet light that's probably what they're weak to because it has a higher energy density than either visible or infrared light."
Nezuko didn't understood any of that, struggling to keep up with the woman's scientific jargon. She knew that demons were weak to sunlight, but she had never stopped to consider why.
"Technically, UV light is harmful to humans as well by damaging our DNA, leading to mutations that can cause skin cancer," Dr. Nova mused. "One hypothesis might be that demons genetically suffer from something akin to erythropoietic protoporphyria, causing them to absorb far more UV light than normal due to the accumulation of protoporphyrin IX."
This time, even Ijin didn't understand what some of the terms being tossed around as he joined Nezuko with their looks of confusion.
"Nezuko has mentioned that, in her world, these 'Demon Slayers' wielded special swords that were the only tools outside of sunlight to kill demons through decapitation. I have never heard of Nichirin before, but I have a theory as to how it might work. Those blades might function through fluorescence. In our world, there are minerals that can absorb UV light and emit them at a longer wavelength, a lower energy than the absorbed light. If these blades were made of some material that can absorb and emit UV light, that can explain why they work against demons."
Nezuko had simply accepted her fate that Dr. Nova will speak a language that she will never understand.
According to Dr. Nova, the fact that Nichirin blades did not emit visible light in of themselves was evidence to support the theory UV light was the main weakness, something that humans cannot see. Had there been something innately special about sunlight in general, these Nichirin blades would have emitted a bright light, but that didn't seem to be the case based on Nezuko's intel.
The charred demon, still smoldering from the burns inflicted by the solar simulator, suddenly fixated on Nezuko. The demon's body was still in the process of regenerating, but his voice boomed with newfound strength and fervor. "You!" he snarled, pointing a blackened finger at her. "I've finally found you!"
Nezuko's confusion was palpable. She had never met this demon before in her life, yet he seemed to know her. "Huh?" she gasped, taking a step back instinctively.