Notes: Whoops, it's me after nearly half a year later. I haven't written a story in forever, my brain is still active and wants to write more. help me.

anyways, please enjoy the story!

—|[0o0]|—

Muzan Kibutsuji was an abandoned orphan, left on the side of the road to starve to death when he was taken in by a reluctant family. He was a sickly boy ever since he was young, the illness was unknown to doctors as they couldn't help him whatsoever. The illness rarely bothered him, it only ever gave him a slight cough from time to time.

He had a peculiar gift that made him different from the others, the gift of enhanced sight. He was able to see things that no one else could. For example, he can see even the smallest muscles move. He knows whenever someone makes a mistake, what emotion someone is going to make and when someone is going to move. He can also see the aura of living beings, whether or not they are present and for him, each aura is unique, although he himself doesn't know-how.

However, Muzan wasn't going to let this ability of his bring him down. He had a life full of opportunities in front of him, and he wasn't going to ignore it.

He decided to work alongside his "father" and farm.

He worked with ease in the fields, his "family" helped him gather enough funds to buy his own house near the mountains which helped him continue farming. He invited his "family" to live together. Through his job, he managed to meet the woman he would later marry and cherish for nearly a decade.

His wife was a headstrong person, her strength came through her words as she had even tamed a person as perfect as him. The two helped move in his wife's parents, his mother, and father-in-law who were ecstatic to see their daughter get married to someone like him. The small act of kindness went a long way as Muzan managed to open his heart a little and respected them as much as he could. Even if he were impeccable, he had to admit that even his elders were slightly better than him.

After nearly a year after the couple had married, they were blessed with two children. One was a daughter while the other was a son. The parents decided to name them Yuki and Ryouichi respectively.

The two children grew up over the years, as their age grew, their personalities developed. They were both currently twelve.

Yuki was a kind-hearted individual who helped her mother out whenever she needed it. She helped prepare meals, clean laundry and most importantly, support her family. She helps to comfort her brother when he comes back from long journeys to the market alongside their father.

Ryouichi had a heart of gold as he would help others whenever they looked or felt down. He would typically help his father with selling their plentiful crops to the nearest town, walking for a day or two to their destination and back. He's quite spoiled by his sister, always being given the most attention whenever he announces he's arrived back home.

Muzan was quite happy that throughout his thirty-two years, no such thing had decided to ruin his perfect life. There was no such thing as a burglar, famine, illness or blemish that had existed in his world. His world was ideal.

He had his house, he had his family and he had his whole life planned out all in front of him. No one could possibly take this away from him.

As long as the heart inside him continues to beat, he will continue to strive for his world. That's what he had said before, now and after.

Therefore, he knew that somehow he was prepared for anything. He knew that going alone to sell his crops was a good idea.

Ryouichi was looking at him fondly with a sad look in his eyes. The boy's hands were curled into a weak fist, he was protesting what his father was doing.

"Father. Why aren't you letting me come with you?" He asked as Yuki was peering over her brother's shoulder, noticing his lingering sadness.

Muzan looked over his shoulder, his comforting stare making his son feel his sorrow being lifted from his shoulders.

Muzan was never wrong. He knew that he didn't need Ryouichi to help him sell this week due to the amount of money they already had. Plus, it was snowing quite heavily during this time of the year. After all, it was New Year's Feast in just a few days. He couldn't take his son with him.

"You have to get ready for the feast. I won't let you skip out on something as important as this," Muzan answered as his son seemed content with his reply.

It was just for two days. They'll survive and he'd be back right on the holiday.

There's nothing wrong.

Ryouichi smiles brightly as Yuki waved.

"See you dad!"

"Goodbye, father!"

Muzan gave the two a nod and started his trek towards the nearest village.

He wondered if his wife were able to make some of her kuromame* for the feast.

—|[0o0]|—

The smell was putrid.

Muzan wasn't sure what the smell was exactly but it was horrid. It was as if he were in a butchery mixed in with rusted iron shavings. He'll be damned if he were able to hold in his disgust.

He looked around, when he was walking back to his house, he had encountered a peculiar old man whom he was familiar with. He had frequently helped to repair any of his tools to farm.

The man had told him to hurry back home as he had told him there were blood-thirsty demons roaming around the night.

Just the idea of demons made Muzan snort. There was no such thing as a demon. Demons were nothing but some figment of some brain-dead idiot's dream.

But maybe he wasn't wrong. That's what he thought as he stopped suddenly when looking at his house entrance.

He saw someone lying on the ground, near the altar where they all had prayed at. It was his mother-in-law. Her face was on the floor, he couldn't see her breathing. There was some type of liquid that she was surrounded by.

Muzan quickly went over to her side but slipped and fell on the mysterious liquid. He tried to growl but it remained in his throat. He just realized what he had slipped in.

This smell was what he noticed when approaching his house.

It was the smell of blood.

He wanted to desperately vomit.

Muzan frantically wiped the blood off his face and hands, helping his mother-in-law sit up. Her throat had been slit, her eyes rolled up to her skull and her mouth wide open as if she were going to scream in fear. Her skin was ice-cold.

She was dead.

Muzan closed her eyes, not willing to see the terror. Suddenly the thought of everyone else flashed through his mind. He had to make sure everyone else was safe.

He left the body behind, going through the different rooms in the household. He screamed his wife's name in fear, she couldn't die. She had to be alive. She had to.

There was blood splattered everywhere he went. It scared him. It threatened his world.

As he ran around, he found the corpse of his parents in Yuki and Ryouichi's bedroom. They laid on the floor, his father with a hole in his chest as his mother had her face torn to shreds. And just outside the room was his father-in-law who had met the same fate as his mother-in-law.

They were all cold.

Were they protecting the children?

Muzan quickly went through the closet or any other hiding spot he could possibly find. They weren't anywhere in the room.

Muzan could see something from the corner of his eyes, the faint lingering aura that not only shocked him but also filled him with guilt.

It wasn't the attack of some wild animals after all. It had the shape of a child, they were short and had the visage of something horrid. It stood near his mother, with their hand on the wall.

How could his family die to a mere child? Were they a demon? Was the old man right?

Demons usually hunt for humans while in the night. You'd best be back to your home as soon as possible.

He didn't want to double-check as he left the room, murmuring the last good-bye to his elders.

He then made his way to the kitchen. It was a mess. It was just as much of a mess as the house. There was food that was still being cooked in the pan on the cold stove, a knife stuck in a ball of cabbage, thinly sliced meat and festive decorations on the walls that hangs by a thread. But nothing could distract him from the fact that the corpses of Ryouichi, Yuki and his wife lay right in front of him.

He saw the aura again in the kitchen, this time it seemed to be choking someone, a single hand lifting someone up. He could only assume it was one of the kids.

Ryouichi was slumped over as his wife and Yuki were lying on the floor like everyone else he had met so far.

Their lifeless eyes looking down on the ground, his wife's body was thrown on top of Yuki. He assumed she did it to protect their daughter.

Ryouichi was holding a knife, it had no blood on it. Whomever had attacked his family wasn't harmed whatsoever.

Muzan gagged. It was too much. The idea of everyone who was family to him passed away was overwhelming.

He touched Ryouichi's hand, it was cold. He had his torso slashed beyond repair.

He then kneeled towards his fallen wife, she had a hole in her stomach and a slash on her neck. She was cold too.

He felt his hands shaking when he rolled his wife's body aside, her beautiful face on such a bloodied and mangled body. He then made his way to Yuki.

Yuki looked surprisingly fine. She didn't have any injuries when Muzan took a glance at her. He noticed there was blood that had matted her hair as he gently picked her up and examined her head. She had the back of her head slammed onto the ground. Blood still leaking from her head.

Wait…

Muzan picked up her limp hand with a spare hand as he laid his daughter's head on his lap. He didn't believe it.

She's still warm.

—|[0o0]|—

Muzan wrapped his daughter in his cloak, hoping that the warmth of the thin fabric could keep her alive. He gave her a piggyback ride down the mountain, trying to get to the nearest clinic or doctor as quickly as possible.

It was night, the darkness would normally make it impossible for anyone to navigate through the forest. But not him. His eyes could see through all of that, he never really acknowledged this peculiar ability of his. The ability to see things that others cannot.

This aura he had seen earlier in the kitchen and bedroom, that was what he saw. The killer.

That burgundy red aura, it took the form of a child. It was faint but he saw it. He saw what he saw.

What he had seen in his house was a demon. A man-eating demon that the old man had told him about. They roam around at night for their prey, bloodthirsty and hungry.

But why didn't the demon eat his family? That was what's so out of place.

Muzan shook his head, he didn't have time to think about that. He had to think about Yuki.

He looked back, looking at Yuki's resting face. There was blood smeared across her face and her hair was a mess. If he could, he would've taken the time to clean her up but now's not the time.

It was snowing heavily. The snowflakes melting when they met with his skin, the wind blowing harshly making Muzan hesitate when taking another step. He might be blown away.

His legs were tired from running. The nearest village was still a few miles away, he just returned from there a few hours ago. If he did it hundreds of times before then he can do it again. He'll do it for Yuki.

Because she was his daughter. And he won't let anyone take away anything from his world again.

"Grrr…"

Muzan trudged on, thinking the sound was nothing but a figment of his imagination. There couldn't be anyone else in the woods other than him and Yuki. But it was night and that could mean demons could possibly attack him.

"Graggh!"

The father turned around to be met with a guttural scream as he felt his body slip and his legs grow weaker. Yuki suddenly thrashed around. He collapsed and slipped off a cliff.

FWUMP!

The journey down was a rough one as Muzan nearly hit his head on a tree branch, the scratches and wounds he'd suffered stung. He managed to land in soft snow despite it all, with only minor injuries.

He groaned as he pushed himself up from the comfort of snow as he stood up slowly. He looked behind him, Yuki wasn't there.

"Yuki!" Muzan cries out. The name rang out but no response.

As he attempted to cry her name another time, he was suddenly interrupted by a voice foreign to him.

"You named this demon?"

Muzan turned to his left, he met eyes with dull blue orbs who had his hand on his daughter's arms. The father felt his heart being ripped out of his chest.

Demon?

The person who spoke was a teen with black hair, sporting a haori with two different patterns on both the right and left sides. He saw with clarity that the cloth was hand-stitched; the right side was dark red as the left was yellow and green, in a complicated diagonal-checkered pattern. In his right hand was a katana, shining blue as it gleamed under the moonlight. While in his left hand, it was occupied.

The mysterious man had a tight grip on Yuki as she twisted around, growling like a feral cat. She tried thrashing around, to her frustration she couldn't free herself.

"Let go of her!" Muzan cried out, a rush of emotions fueling his body. He rushed forward, blind to what happened next as he felt something gut him in the stomach. He dropped to his knees as he gasped for breath. His eyes saw what happened.

He's so fast!

The swordsman hit him using the butt of the katana he held. He didn't even loosen his grip on Yuki while doing that.

"Are you dense? I expect you to know better than to protect something like this," the other said as he looked down on Muzan, trying to sit up. "Do you know what this is? This is a demon." The man then fluidly moved his blade up to Yuki's neck, the katana barely making contact with skin. "I am a Demon Slayer, it's my job to exterminate their kind."

"Don't kill her! She hasn't hurt anyone! She isn't even capable of hurting others, not even her own family!" Muzan retorted. He clenched his fists as he glared at those blank and empty blue eyes. "My family was killed by someone else, possibly another demon! I saw someone else at the scene, they're to blame!" Muzan then growled. "If anything, I don't know why Yuki is acting like this! Maybe it's because you're holding her captive! Yuki would never eat anyone!"

"This is simple. Her wounds were exposed to demon's blood," the teen countered calmly as he kept his blade steady. "This is how man-eating demons multiply, so it's most likely the demon who killed your family spilled their blood onto your daughter's wounds."

"That doesn't mean anything!" Muzan shouted. "My daughter hasn't eaten anyone! What makes you think she'll do that to me?"

The swordsman frowned slightly. "Because I've seen demons eat their families, regardless of their previous bonds, eat them because they wanted to. They are naturally bloodthirsty and will kill whenever. Your daughter will most definitely kill you as well if I set her free!"

"How would you know anything about her?!" Muzan managed to stand back up, fiercely bared his teeth. "I know I can save her! There has to be a cure to turn her back into a human! So I'm begging you!" He never begged before. "I'm begging you to not kill her, to let her live and to prove that she won't hurt nor eat humans! I know she's not above killing because I'm her father! So please," Muzan then desperately stifled back a sob. "I beg of you to let her live."

For the first time in his life, he had begged. He never begged for anything up until now. He was begging for his daughter's life. He knelt and bowed his head touching the cold freezing snow.

Human or not, it was a life that was going to be reaped for no reason. And he wasn't going to let that happen.

"Don't you dare beg! I could've killed you and your daughter whenever I could and yet you still beg to live?!" The dark haired swordsman shouted. "How ridiculous! You say that as if you're strong but in reality you're just a weakling with no other options but to beg! Let's say if you did find a way to find your daughter a cure to turn her back into a human? But what if it's only in the hands of a demon lord? I highly doubt that someone like you is able to be respected by them with this story of yours. And I don't expect you to respect them back either with that attitude of yours!"

"So I'll tear the cure right out of their hands then!" Muzan yelled.

"What if you can't?! How will you even protect your daughter in this state?" The teen then gripped tighter, making Yuki howl. Her hazel eyes were looking at Muzan, her cat-like slits for iris looking at him as if he were prey. Her hair was down except for one loose ponytail on the right side of her hair. Her yukata was ripped, her sleeves ruined and her sash was bloodied.

The teenager then readied his katana as he had no more words to say.

(If only I had come sooner.)

SHINK!

Before Muzan could protest any further, the teenager plunged his blade into the left shoulder of Yuki.

"Gyaagh!"

"Yuki!"

Before Muzan knew it, he threw a rock as hard as he could towards the boy; hoping it would distract him. The boy easily blocked the rock with his hilt. Another rock was thrown but dodged once more.

Yuki growled angrily as her body began to contort, her limbs growing longer and physically growing taller. Her arms were bigger, they couldn't be restrained by one meager hand no longer as Yuki twisted around and kicked the boy away.

The swordsman regained his composure as he stood tall, in a battle stance. His katana steady as he saw the demon rush forward Muzan's kneeling figure.

Crap! The swordsman rushes towards the demon. He'll be eaten if he doesn't get away!

He readied his blade for the kill until–

"Grah!"

He stopped suddenly, to be met with the demon spreading her arms out in front of her father. Her fangs bared in anger and her eyes piercing in the cold weather.

It was as if she was protecting the man behind her–

No. She was protecting the man behind her. She was protecting him from the blade in which he almost swung to kill.

Yuki would never eat anyone!

.

.

.

So what he said was true. She might be different from the others.

Yuki, threatened by the still blade, leapt towards the swordsman. Her long nails ready to attack and her fangs bared.

Perhaps he should give them the benefit of the doubt.

WHACK!

—|[0o0]|—

Muzan was shocked as the man in front of him hit his daughter in the neck, immobilizing her as she fell into the snow. Muzan hurried to pick her up, hugging his daughter. Yuki's body shrunk back into the body of a twelve year old.

The father looked up angrily at the swordsman for an answer. The teenager merely looked somewhere else, sheathing his blade back into his saya*.

The teenager took something out of his haori, Muzan frowned as he carefully analyzed what the boy would do next.

It was a piece of bamboo. The boy threw it towards Muzan who caught it, curious.

"Put that on her mouth, make sure she always has it on her," the swordsman said as Muzan nodded as he was then also given a string of ribbon.

He took to work as he tied the bamboo around Yuki's mouth, double-checking if she was biting on it.

"So, do you trust her?" Muzan asked tentatively, as he picked up Yuki in his arms. The snow was faltering but the wind picked up.

The teenager had no comment as he started walking away into the thickets.

"Look for an old man named Urokodaki Sakonji who lives at the foot of Mount Sagiri." The teenager said as he turned around. "Tell him that Tomioka Giyuu sent you. It seems like a good time for you to hurry out, it's dark and the sun doesn't seem like rising right about now. Demons can die when exposed to the sun, so don't take your daughter when the sun is out."

"Thank you. You said you were a Demon Slayer right?" Muzan asked. "I want to find the demon who did this to my family and kill him! I'll become a Demon Slayer!"

The now identified boy, Tomioka, seemed content with Muzan's words as he turned back around and walked into the darkness of the mountain.

And Muzan was alone again with Yuki. Muzan ran his fingers through Yuki's hair, her light brown hair tangled with knots. He could feel his tears trickling down his cheeks as he hugged Yuki even tighter.

He never felt this way before. This feeling of hatred and vengeance.

And the rage just kept piling up.

—|[0o0]|—

Yuki opened her eyes. Her hazel eyes glancing around the area, turning around to see the man that she was protecting.

If only she understood why he was crying when he saw her open her eyes.

—|[0o0]|—

Definitions:

Kuromame: A dish consisting of sweet black beans.

Saya: The scabbard of a katana.

—|[0o0]|—

Notes: I would just like to say thank you so much for reading this mess of a fic. I have no idea what went through my head during the time I wrote this fic because I just woke up in the middle of the night and thought: "what if muzan swapped with tanjiro and his unnamed daughter swapped with nezuko?" It's really weird trust me.

I've decided to give Muzan's daughter a name: Yuki. I know it isn't creative but I tried.

I'm also very sorry that I didn't get to describe what the Kibutsuji family looked like in this fic. To clarify: Muzan's wife and daughter looks the same as they looked like in canon. And in the manga flashbacks, Muzan had pretty long hair so I'll be implementing that into his looks in the fic.

I'll probably try to draw what the family looks like, digitally, hopefully.

Anyways, I'd like to thank you all once more for reading! If you have any questions, please ask them! I'd be more than happy to answer them!