Chapter Text
Kokushibo stood silently. He could sense a Demon Slayer in the distance. Not a particularly strong one, most likely a beginner. He decided to kill the Demon Slayer now, so the problem wouldn't snowball into a huge problem in the future.
Kokushibo approached the forest with a calculated gait, the moonlight guiding his path. He didn't bother drawing his blade, the Slayer he sensed was weak. He entered the forest and his form disappeared into the shadows of the trees, the scent of death and demon lingering in the air as he closed in on the weakling.
Then he spotted a flicker of a green and black fabric between the trees. Soon the Demon Slayer came into view.
...When Kokushibo called the Demon Slayer young, he didn't expect for the Demon Slayer to be a teenager, a mere child. Was the Demon Slayer Corps allowing children to pick up a blade nowadays?
This caused for Kokushibo to actually halt.
A child.
A mere, weak child.
The Demon Slayer Corps was allowing children to fight. Kokushibo's eyes flashed with anger and a hint of disappointment.
"The Demon... Slayer Corp... allowed children... to take up... blades now?" Kokushibo growled, his voice filled with a mixture of anger, disappointment, and a hint of disgust. He had to admit, not a lot of things could make him loose his temper, but it was both amusing and infuriating to even think that a child so young could cut a demon's neck.
The young Slayer's appearance didn't help to ease his anger. The boy had ruffled burgundy hair, wide, dark red eyes with white pupils that appear lighter around the lower section of his irises, and a scar on his forehead. The scar was somewhat similiar to the scar Yoriichi had.
Not to mention the Hanafuda earrings that hung from the child's ears.
The child looked nothing similiar to Yoriichi, yet the memories of his brother resurfaced everytime he simply glanced at the Slayer infront of him.
Finally the young Demon Slayer spoke up. "I-I am not a child." The Slayer said, his voice trembling with fear and nervousness. He was a mere child faced with Upper Moon 1.
Kokushibo's anger flared even more upon hearing the child's words. He felt a mix of anger, annoyance, and almost disappointment. He couldn't believe that this child had the audacity to try and deny his own age.
It was bad enough that the child looked like Yoriichi, and also the fact that he was a child holding a sword and fighting demons.
Kokushibo stared down at the young Slayer for a moment before speaking, his voice icy and sharp. "Do not... lie to... yourself, boy."
The Slayer flinched briefly at his tone, but surprisingly managed to tighten his grip on his blade in determination. "My name is Tanjirou Kamado! And while I might not be an adult I still can fight demons! And I will never give up!"
The child, Tanjirou Kamado, was filled with determination, which was admirable and also foolish. While it was admirable that a human this age and in this situation could be so determined. But the child was too determined to complete his duty as a Demon Slayer, which apparently results in him not backing away from Upper Moon 1.
The child's determination caught Kokushibo off guard for a moment, he almost felt impressed by the young Slayer's courage. Even in the face of Upper Moon 1, Tanjirou Kamado refused to back down.
Admirable...
But also...
Foolish.
Kokushibo shook his head, his voice filled with a mixture of anger and respect. "You have... courage, boy... I'll give... you that... But courage... alone will not... save you from... a battle with... Upper Rank 1... or any other... demon for... that matter."
"I am aware." Tanjirou took a stance. "But that doesn't mean that I'll simply give up."
Kokushibo watched as Tanjirou took a stance, his eyes narrowing. He was impressed by the child's determination, but at the same time, he knew that he was no match for an Upper Moon.
"You are... braver than most... I'll give... you that." He took a few steps forward, his hand resting on his katana. "But you're a... fool if you... think you can... win this fight."
Tanjirou tensed a bit when Kokushibo moved and raised his sword to attack. Kokushibo dodged the child's attack with ease, barely moving an inch. He observed the child's form, focusing on his technique.
Water Breathing.
The child's technique was sloppy but he could see a hint of potential and talent hidden beneath the layer of inexperience.
"This child... possesses potential... If time and training... were on his side... he could... become quite strong..." Kokushibo noted.
The thought of such a young child possessing potential didn't sit well with Kokushibo. He had been expecting an easy kill, not a potential prodigy.
As Tanjirou continued his water breathing attacks, Kokushibo couldn't help but be reminded of Yoriichi. The way he moved and fought, his potential, it was almost like looking at his younger brother-
NO.
Kokushibo forcefully shook away the memories. He couldn't let himself be distracted by memories of Yoriichi. He had to focus on the present, on the child attacking him with all his might.
As Kokushibo dodged the attacks, he took a glance at Tanjirou's blade, and he couldn't help but notice the color - a deep, obsidian black. It was all too similair to Yoriichi's sword, which had been the same shade.
The resemblance only fed his anger and frustration. It was as if Fate itself was mocking him, dangling a reminder of his younger brother right infront of him in the form of a mere child.
A feeble child. A weak child somehow fighting demons.
Tanjirou took a step back to gather his breath and probably just wonder how he's still alive. Then he took a complitely new stance and attacked.
His breathing technique changed. He was using Sun Breathing now.
Kokushibo's eyes widened in surprise. How... How did a child possess the knowledge of the first breathing style, the most powerful and ancient one?
The sight of this mere child using Sun Breathing was a shock to Kokushibo. It shouldn't be possible. No one was supposed to be able to replicate the technique. It had died with Yoriichi Tsugikuni, the man who created the technique.
Yet here was a young boy, wearing Yoriichi's earrings, wielding a sword of the same color as Yoriichi's, and using his technique.
It was baffling, infuriating, impossible.
The changes in the air as Tanjirou breathed and wielded his sword were undeniable. Kokushibo could feel it.
It was real.
The child was using Sun Breathing, although not as precise as Yoriichi's, it was still a masterfully executed technique. Despite the flaws in Tanjirou's attacks, it was still impressive. But that only made Kokushibo angrier.
Why was this child, of all people, able to use Yoriichi's technique? Where did he learn it? How did he even learn it? Who taught him? How did this child, this child, learn the most ancient and powerful breathing style in existence?
The questions went on and on, and for once, Kokushibo was truly baffled.
Kokushibo's mind was racing with questions, his focus slipping for a split second. In that momentary lapse, Tanjirou managed to land a hit.
The child's blade tore through the sleeve of Kokushibo's kimono, but it was not the physical damage that caught his attention.
It was the fact that Tanjirou had even managed to touch him in the first place.
This child possessed a dangerous combination of talent, skill, potentional, and the ability to use Sun Breathing.
Kokushibo studied Tanjirou closely. There was no denying it. The child had immense potential. His ability to wield Sun Breathing, a style that should have died with Yoriichi, was evidence enough of that.
Yet this potential was hindered by his very humanity. His human limitations and lack of experience held him back. It was a shame in a way. Had he been a demon, with all that talent and skill, he would have surpassed even the Twelve Kizuki and made it into the Upper Ranks.
The idea of turning Tanjirou Kamado into a demon had initially been fleeting. But the more Kokushibo considered it, the more it made sense.
Yoriichi's legacy would be truly tainted if his successor, this child with such tremendous potential, became a demon.
It was almost as if Fate itself was presenting him with a chance to ruin Yoriichi's memory once and for all.
The appeal grew with every passing moment.
With a swift movement, Kokushibo drew his blade. It was the final blow. In one fluid motion, the demon aimed his weapon at Tanjirou. He swung his sword, and the blade cut straight through Tanjirou's arm.
The limb detached from the rest of Tanjirou's body with ease, leaving the child in a state of shock and pain. But despite the injury, the child somehow stood his ground, applying pressure to his bleeding limb. Kokushibo was slightly surprised by the boy's resilience.
Observing the wooden box strapped to Tanjirou's back, Kokushibo noticed it shake slightly.
It appeared there was something inside it.
Tanjirou, however, was too preoccupied with his bleeding arm to pay it any mind. Kokushibo's interest was piqued. What could possibly be inside that box?
Something from the inside kicked the door open, and a young girl jumped out. Her hair is long, black, and wavy. It reaches just below her waist, turning a flame-orange color as it passes her elbows. She has pale pink eyes with slits, a black haori ontop of a pink hemp-leaf kimono. She has a bamboo muzzle covering her mouth.
She's a demon. But for some reason she's traveling with this Demon Slayer, and seem quite angry at Kokushibo for slicing Tanjirou's hand off.
"N-Nezuko!" Tanjirou cried out. So her name was Nezuko? Were they siblings? They looked somewhat similiar.
Nezuko let out a growl and clenched her fists, her veins popping up from sheer rage.
Kokushibo recalled Muzan mentioning something about them needing to kill a traitor demon other than Tamayo. A young girl with a pink hemp-leaf kimono and a red-and-white-checkered obi. This girl was the demon that somehow escaped Muzan's control.
Muzan's order echoed in Kokushibo's mind, reminding him that Nezuko Kamado was to be eliminated.
However, nothing had been said about Tanjirou.
The idea of turning Tanjirou into a demon was more and more appealing to Kokushibo.
Suddenly, Nezuko lunged at him, her leg raised high for a powerful kick. Yet, her weakness was palpable. She was a weak demon with minimal human consumption.
So the demon girl really stood no chance when Kokushibo raised his sword and took care of the problem. One second Nezuko is bringing her leg down to possibly kick Kokushibo's head off, and the next her body is severed in two.
As Kokushibo effortlessly dispatched the demon girl, Tanjirou let out a panicked cry, calling out his sister's name.
In his distress, Tanjirou momentarily forgot about Kokushibo or his severed arm that was still bleeding and the fact that he had nothing to defend himself with.
Tanjirou's concern for his sister outweighed any considerations for himself. It was a endearing and somewhat admirable trait, albeit a little reckless and foolish.
Nezuko's lower half was far away from her upper half, and the force of her upper torso being slammed to a nearby cliff caused a large boulder to fall on top of her. So she's now stuck there and will perish when the sun comes up. She's unable to lift the heavy rock off of herself due to her other hand being underneath it as well.
Kokushibo turned his gaze back to Tanjirou, who was now visibly panicked. The loss of blood and the mounting pain were taking their toll on the child.
Tanjirou was starting to wobble, struggling to maintain his balance as he leaned heavily against a nearby tree, looking like he was about to lose consciousness at any moment.
With a swift movement, Kokushibo stepped towards the weakened Tanjirou, who was desperately trying to stand, his back leaned against the tree.
As Kokushibo approached, Tanjirou instinctively flinched and stumbled back, visibly afraid.
It was the first time during their entire exchange that Tanjirou's eyes had held a trace of fear, a stark contrast to his previously defiant demeanor. Yet, Kokushibo could spot a hint of worry. Worry for his sister. Despite his fear of what might happen next, he was still worried for his sister more than worried for himself.
Admirable, but not helpful to the two siblings. Kokushibo was quickly infront of Tanjirou and the next thing the boy did was cry out in pain when Kokushibo stabbed his sword through the boy's torso to pin him to the ground and keep him from moving.
As Tanjirou gasped for air to try and stop the bleeding, like that would help him, Kokushibo dug his claws into his palm, drawing out blood. Tanjirou's eyes widened in horror as he realized that Kokushibo wasn't going to kill him, instead he was going to turn him into a demon.
Despite Tanjirou's attempt to turn away, Kokushibo was having none of it. He dug his fingers into the boy's jaw, forcing his mouth open, and held his head firmly in place. Tanjirou's eyes widened in panic, his body trembling in fear of the inevitable.
Tanjirou managed to weakly grab onto Kokushibo's wrist, but he wasn't able to do anything else and was helpless to do anything when the blood poured into his mouth.
Then Tanjirou Kamado was no longer human.