Chapter Text
The only thing that ever truly consumed Muzan Kibutsuji's thoughts, beyond his relentless pursuit of the Blue Spider Lily, was the enduring phantom of Yoriichi Tsugikuni. Decades, centuries even, had passed since that humiliating, near-fatal encounter, but the memory was a festering wound in his immortal soul. The sheer, unyielding power, the casual way Yoriichi had nearly eradicated him – it was a trauma that fueled an obsessive, unending search. Muzan knew, logically, that Yoriichi had no descendants who could wield the Breath of the Sun, yet the fear gnawed at him, a constant, chilling reminder that a vestige of that terrifying strength might still exist, hidden somewhere, somehow. He had deployed countless demons, scourged villages, and meticulously scoured records, driven by a paranoia that demanded the complete eradication of even the faintest whisper of Yoriichi's legacy.
His frantic, tireless search for any remnants of that sun-kissed terror continued until a new report from Nakime. The mundane details were dismissed at first: a family living quietly in the mountains, making their living by selling charcoal. Harmless, unremarkable, utterly beneath his notice. But then, as Nakime calmly relayed the more obscure observations, a single detail pierced through Muzan's carefully constructed indifference, striking a chord of ancient, visceral dread. Their eldest son, she droned, was often seen wearing a pair of distinctive hanafuda earrings – the very same, unmistakable design that Yoriichi Tsugikuni had sported all those years ago, dangling from his ears as he wielded the blade that nearly ended Muzan's existence.
The calm façade Muzan always wore barely rippled, but a cold, calculating fury ignited within him. Coincidence was a luxury he could not afford when it came to Yoriichi. This was not a task for a subordinate; this required his direct, absolute attention. There would be no investigation, no lengthy observation. Only swift, brutal obliteration. The thought of even a distant connection to the demon slayer who had once pushed him to the brink of death was intolerable.
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“Mom! I’m going down to sell charcoal!”
“Again, honey? We have enough.”
“No, no! I want my younger siblings to have more. But I’ll be super quick. Don’t wait up for me!”
“Please do come back soon.”
“I will Mom, don’t worry!” He said as he waved while walking down the mountain.
She really thought she was the luckiest mother ever. Even though her family didn’t have much, she knew that they were rich in ways that mattered more than money. Her son worked relentlessly for his family and had a unique kind of sparkle in his eyes that can never be worn down. He was smart, kind, helpful, selfless, brave, and most of all so empathetic. He always knew when his siblings were sad and exactly how to cheer them up. After their father’s death, he took up the mantle as the man of the house and worked like there was no tomorrow.
She was hanging clothes when it happened. When tragedy struck their family. She could hear crying coming from inside.
“Nezuko? Calm down your brother. And tell Takeo to come clean up his mess.”
No answer.
“Nezuko?” She said louder, maybe she didn’t hear her.
“Nezuko?” This time there was panic in her voice.
“TAKEO? HANAKO, SHIGERU?”
She immediately dropped the clothes and hurried inside the house. The first thing she saw was Rokuta’s head on the wall. The rest of them were scattered across the floor, limbs dismembered, eyes out of sockets, flesh torn apart with gore and blood everywhere. It looked like something straight out of the horror folklore of the village.
From across the room stood a tall, slender man with blood red eyes, dark wavy hair, and dressed in a white suit. He looked at the woman with a playful expression.
“I had a little fun before killing them.” He said as if telling a secret. His voice was low and soft. She stared back at him, her eyes holding a fury only a mother’s could. “Sorry about your walls.”
All she could do gape when he made his way to her and twisted off her head.
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“Mom! I’m back! I sold charcoal to ten people too!”
His nose twitched and he could smell blood and something unfamiliar coming from inside the house.
“M-Mom?” There, or more like everywhere, was his family. The scene was an absolute horror. His chest felt constricted and he stopped breathing. He silently started crying and took heaves of air at a time. He didn’t know there was someone else in the house until he materialized right behind him.
Muzan saw the hanafuda earrings as soon as he entered the house. He planned to kill him like the rest but there was something else about him that made the air shimmer, a faint, ancient scent clinging to his spirit, stirring the unease that brought him to this house in the first place in Muzan's core. It was a ghost of the Sun, barely perceptible, yet undeniable – a lineage he had relentlessly pursued and eradicated. And beneath that, raw, untamed potential, a resilience that even in abject despair, refused to break.
"How... fascinating," Muzan murmured, his voice a chilling purr from behind Tanjiro. The boy whipped around, his face streaked with tears, eyes wide with horror and despair, then a spark of pure, desperate rage ignited within them.
Muzan watched him, a slow, predatory smile stretching his lips. He had intended to simply complete his work, but this boy... this was an opportunity he hadn't foreseen. A chance to twist a potential threat into his ultimate weapon. To corrupt the very essence of what he feared most.
“That’s too bad. Not too bad about your family’s deaths though, too bad you weren’t strong enough to save them. Too bad they won’t get to see tomorrow. Too bad your youngest brother never got to experience life. It’s just too bad that you were a burden, no a curs-,”
“SHUT UP.” Tanjiro cut him off. “SHUT UP, SHUT UP, SHUT UP!” There were a lot of things Tanjiro could put up with. When Takeo had accidentally dropped his rice ball down the mountain, he gave him his own. When nezuko had to go down to the village, he took care of their youngest brother while still doing his daily duties. But there was one thing he couldn’t put up with and that was harm done to his family. Whether it was verbal, physical, emotional, or mental. So when Muzan did all of the above to his family, he was enraged. Even worse, he insulted their honor.
“YOU DON’T KNOW ANYTHING ABOUT MY FAMILY. NOT ONE SINGLE THING. SO I’M NOT GOING TO SIT HERE AND LISTEN TO YOU SLANDER THEIR NAME!”
“Fiery and passionate. Yes, the makings of a loyal demon. You misunderstand. I merely observe. And what I observe is weakness. The weakness of your kind.”
“Demon? Demons aren’t real,” Tanjiro spat, his body trembling, not just from cold, but from sheer terror and indignation. His eyes darted around, searching for a way out, a weapon, anything.
“Oh, they are very real. And you stand before one. Look at this destruction, boy. Look at what your helplessness cost you. Do you truly believe your human strength, your tears, your pathetic rage, could have prevented this? Could ever prevent anything like this again?”
He took a slow, deliberate step forward, and Tanjiro instinctively recoiled. “I offer you more than a meaningless struggle. I offer you a truth. The truth of power. Imagine… unimaginable strength. The kind that crushes all obstacles. The kind that ensures no one you care for ever falls again. The power to seek true retribution, not just for this, but for every injustice in this fleeting, fragile world.”
Muzan extended a hand, the pale skin almost luminous in the dim light. “You stand alone now, broken and powerless. But I offer you a gift. A gift that will transcend your human limitations, that will transform your grief into a force capable of reshaping your world. You could stand above this pain. You could become truly strong.”
Tanjiro stared, his breath hitched. The words, poisonous as they were, resonated with the raw, gaping wound in his soul. Unimaginable strength? The image of his family, lifeless, flashed behind his eyes, mixing with a desperate, burning desire for power—the power to prevent this, to make them proud, to make someone pay. His rage mixed with despair, and a horrifying, seductive logic began to whisper in his mind. His trembling ceased, his gaze fixed on Muzan's hand, a dark spark flickering in his tear-filled eyes. He didn't want to give in, but the sheer exhaustion, the overwhelming grief, and the promise of absolute strength were a heavy, suffocating blanket.
Just as the barest flicker of resignation, a desperate yearning for what Muzan promised, crossed Tanjiro’s face, Muzan seized the moment. With a swift, almost imperceptible movement, his long, sharp fingernail pierced Tanjiro’s neck, and a searing, burning sensation erupted through his veins, the demon’s blood flooding his system.
As Muzan carried him into the night, Tanjiro began to stir. He felt different in a way that he could have never imagined. As he stood up, he felt a fiery warmth spread throughout his body. He walked a couple paces before running around with a crooked grin on his face. Beneath a demon moon, his eyes shone even more brightly than before.