Fog-enshrouded mountain a few kilometers west of Asakusa, bringing a sense of eeriness into the vicinity. To any passerby at this moment, this mountain felt no different from hell itself. Its famous tourist destination, the Kirigato waterfall, plummeted downwards just as usual, but with the scent of blood. The water, which was painted red, further gurgled downwards from the hut located at the peak of the mountain.
At this very moment, heinous crimes were being committed at the hut. Muzan Kibutsuji, who was just a passerby, had spotted this hut. The demon king wanted more subordinates, useful ones that would not be swatted around like flies by the demon slayers. Despite not having any hope, he still decided to take a chance—one that he would later on remember as the best decision he had ever taken.
The family that had caught Muzan's attention was a family of four, and at this moment, they were about to have dinner.
"Saeto, Thank you for going down the mountain and getting the vegetables. Without you, I don't think we could have ever enjoyed such a meal."
The boy who was being praised by his mother was Saeto. He was someone who had always been diligent and hardworking. As the family gathered around the dinner table, the main door of their house was suddenly torn through.
Within a second, a thin thread like marking lay on his parent's and sister's neck. Saeto thought he was hallucinating, until the heads of his dearests fell to the floor with a resounding thud. Blood oozed through the lifeless heads as the entire floor looked bloody red. Seeing his loved ones perish within a moment gripped Saeto's very soul. Tears dripped uncontrollably as Saeto let out a painful yet horrid scream.
"Ara--Ara. How fascinating," The true perpetrator of this incident appeared. He didn't just appear; he approached while casually kicking away the mutilated bodies of the deceased.
"Yo....u! You are a demon," Saeto muttered while feeling truly hopeless; he felt his weakness gnawing him down. What could somebody like him, a mere human, do against a demon?
It was in this trauma that an inexplicable transformation took place within the boy's head.
"Contrary to the situation, the boy murmured."Huh, where am I?
"Holy what the f*ck! Why is there blood smeared on the walls? Is that Muzan? Am I in Demon Slayer?
His contemplations soon came to an end as he felt a piercing pain on his forehead. A black haze enveloped him, taking away his consciousness.
A few hours went by, with the boy waking up in a narrow, candlelit passageway. Opening his groggy eyes, a wave of dizziness enveloped him. He smelled something appetizing, exquisite, and mouthwatering. Little did he know that the delicious smell had slithered into the cracks of his mind.
Feast.
A voice resounded within his head—one that awakened his primal instincts.
Kill.
Now the voice hammered against his head repeatedly. Saeto lost control of his body, entranced by the voice in his head. 'Kill, kill, kill," he robotically muttered.
Rip. Tear. Feed. EAT.
A cacophony of voices continued ringing inside his head. It was at this moment that his last remaining shreds of consciousness resisted. "Stop!" he gasped aloud, slamming his palms to his temples. "This isn't me. I'm not—!"
They're weak. Soft. Bleed easy. Just a bite. Just a taste.
The shadows pulsed. He could feel his fingernails digging into stone, carving it like butter. His jaw twitched. Had his teeth always been that sharp?
Had Muzan turned him into a demon? Were his secrets going to be exposed? "No. No, no, no—" he stumbled back, scraping his shoulder against the wall.
You were born to devour.
"Shut up!" he screamed. But the echo of his own voice sounded inhuman now—layered, distorted, like two voices trapped in one throat.
Just eat!
A final voice rang inside his head before the boy lost control. In a flash, like a wild animal, he disappeared towards the lingering smell—dead little children.
The boy's fingernails dug into each child's chest, removing a muscular red organ. He held every organ in his hand before crushing it into a pulp. He then reached out to grab the heart, turning it into a horrid amalgamation of veins. The boy licked it clean and then feasted on every piece individually.
Despite feasting on every single organ and every piece of flesh, the insatiable hunger within the boy only worsened. It was at this moment that a voice in his head sounded. Good job, Saeto! You have passed my first test."
As the voice disappeared, Saeto experienced another splitting headache.
"Who am I? Why am I committing such heinous acts? Did I just consume innocent children?
"Screw you, Muza...." Just as he said that, the veins inside Saeto's body bulged with blood gurgling and spraying. It seemed like stating out Muzan's name loudly was not a good idea. The screams continued, with the torture ending after nearly an hour.
A heavy silence followed the screams, broken only by the gentle footsteps of a man walking towards him. A man with crimson eyes, a black cloak, and a white hat. The man was Muzan, standing a few paces away, arms crossed, observing with an unreadable expression.
"Ara--Ara. It seems like this was a worthwhile endeavor," Muzan murmured, tapping a slender finger to his chin. "Your mind... it is unlike any I've seen before."
Saeto's body slumped against the wall, chest heaving, eyes wide with confusion and fear. His hands, which were soaked in red, trembled with disbelief. His lips, glossy with gore, muttered.
"Kamados... the... mark... what mark?"
Muzan's smile widened.
There were the fragments of images, memories, and names. Names the Demon King had never heard, but now they swirled in front of his mind like glimpses of a broken prophecy. A scarred boy with a blade of sunlight. A Hashira cloaked in mist. A girl with a bamboo gag. All of Saeto's previous memories regarding Demon Slayer were now exposed.
"These... aren't hallucinations, or are they?" Muzan whispered. "You know things, don't you, Saeto?"
But Saeto couldn't respond. The pain was returning.
His eyes glazed, and as he stumbled to his feet, he caught sight of a glint beneath him. A shallow puddle of water, dyed red, reflected the flickering candlelight—and his face.
He froze.
His reflection blinked back at him—barely human.
Porcelain-white skin, now etched with thin, black veins that pulsed like roots. His sclera had darkened, irises now a glowing, hateful gold. And worst of all, his mouth… it was still chewing as a piece of someone's throat hung from one fang.
He screamed.
"That's not me. That's not—!"
The puddle rippled as a reflection of him tilted its head... and smiled.
"You are me, Saeto."
The voice was no longer external. It lived in him now.
"You are me"
The thumping noise again resounded in Saeto's head. It was a voice he could not resist; it was a voice that consumed him; it was a voice he had to bow down to.
With his stomach gurgling, Saeto needed flesh; he craved it. He needed to find a town, one that harbored delicious humans. With Muzan's permission, he leapt across the cave and disappeared into the shimmering moonlight. It was at this moment that Saeto's primal instincts were starting to take over his morality.
As Saeto was travelling, he suddenly caught a whiff of a delicious aroma. "Humans? his raspy and shrill voice exclaimed."
Saeto treaded through the darkness of Aokigahara forest, hunting for those humans through his strong sense of smell. After a few hours of tracking down, he caught a glimpse of his prey from afar: a group of humans adorning a ridiculous uniform while holding katanas.
A cacophony of commands resounded in his head. "Kill, kill, kill, and kill!" Despite his primal instincts giving in to those temptations, a certain consciousness in his head still showed resistance. "I must not succumb...mmb." Just as Saeto's desperation grew, a final voice resounded in his head.
"Kill those scum."
In his mental space, Muzan Kibutsuji commanded him to take action, and guess what? His body responded, preventing any disobedience.
As Saeto jumped on to a nearby tree, his action did not go unnoticed, with an orange-haired slayer from the Rengoku family warning everybody else. He was a Hashira, proven by the golden buttons that were neatly adorned on his outfit. With an arrogance that matched his rank, he remarked."This demon is courting death."
In a flash, the Hashira disappeared, instantly appearing next to Saeto with his sword swinging sharply to cut the demon's head. The Hashira thought he was successfully going to sever the demon's head; however, his face quickly transformed into a frown as he noticed the kanji (Upper Moon 5) engraved into the demon's irises.
Even Saeto himself was unaware of this development. Yet right now, he had more pressing concerns to attend to, especially with a sword threatening to sever his head.
"Kekkijutsu (血鬼術) Art of Flesh Desecration" (肉穢の術, Nikuwae no Jutsu)
"Marionette Maw (糸呑み - Itonomi)"
Suddenly, an amalgamation of black rotting fibers descended from the Saeto's back and the cavity in his chest. These tendrils clashed against the Hashira's sword, forcing him backwards while creating a huge disaster—one where nobody except the Kinoe in the slayer's group survived. The tentacles pierced all the remaining slayers as blood and organs splattered across the dense, muddy, and moss-covered earth.
Wreathed in blood—this was the only phrase capable of describing Saeto's current state. A slow but steady grin spread across his face as he madly licked all the blood splashed over his body.
Seeing all his fallen comrades in such a state left the Hashira deeply scarred. One by one, his eye sockets swelled, bursting with blood. A deep fury, an unrestrained one, was brimming within the Hashira, one that he was ready to unleash.
The Hashira's eyes were locked on to Saeto's, his hands trembling as he remembered his fallen comrades. But he failed to notice that behind him, two of his fallen comrades suddenly got up. Their eyes were hollow and lifeless, and yet, they stood there, grabbing their fallen swords. Like puppets, they leaped towards the Hashira, with uncontrollable tears falling from their eyes.
Just as the two puppets now entered striking range, the only surviving slayer, a Kinoe, quickly warned Rengoku. "Ren...gok...u sama! Behind you!"
The Hashira quickly turned behind, his emotions betraying his actions. And upon seeing the teary eyes of his companions, along with their contorted bodies, the Hashira went into a trance.