A/N: First things first: I know there are already a LOT of Roleswap AUs out there- probably more well thought out and interesting than mine- but this is my personal take on it. The ideas for this has been rolling around in my head ever since I finished the manga, and I could not *not* write it. Kimetsu no Yaiba is a fantastic manga with fantastic characters. I thank Koyoharu Gotouge for creating them.

I took liberties with Nezuko's character. I hope that is alright. Nezuko would still get a lot of "screen time" but despite this being a Role Reversal AU, Tanjirou would still be the main protagonist of this story. It will still focus on his point of view, his struggles as a demon and as an older brother, etc., etc. At the end of the chapters, there will be a segment called "Taisho Secret", where I will put other additional (sometimes not exactly relevant) information that didn't make it into the story for one reason or another.

I will try to update weekly. I have already finished around ten chapters, though they are yet to be edited. I will continue to write it this AU as long as I derive pleasure from it. If you take the time to read it, thank you very much. :)

WARNING: This story is a little bit gay. Not too much, just a little bit. Still, if you're determined to be homophobic, get out. Thanks.

Chapter One: Cruelty

Whenever happiness is destroyed, there is always…

"Onii-chan!"

His finger twitched, ears reaching out to hear that single, teary-eyed voice. A familiar voice, one he had heard nearly his entire life, and yet for the life of him, he could not remember whose it was. His entire body ached, his nose twitching to the sickly sweet smell that made his stomach roll itself over in knots, hunger making it feel like his insides were eating itself ten times over. Something was wrong. Something was really, really wrong.

"Onii-chan, please wake up!"

The sound of struggle. Someone was trying to move his body, drag him from where he was laying face down on the snow, but whoever it was did not have enough strength to even pick him up, and the sobbing was only getting louder every second. He wanted to reach out and comfort it. He wanted to touch her cheek and tell her that everything will be alright. But even at his confused, mind-addled state, something was telling him that nothing was ever going to be alright again. They'd lost so much, he'd lost so much… all because he was too weak to protect them, to protect his entire world.

Something inside him wanted to cry. Something inside him wanted to scream. Something inside him wanted to eat, eat, eat— the ravenous hunger seeking to overtake all of his emotions, the sickly sweet scent he had smelled earlier coming back to him with a vengeance, overriding his senses, and the next thing he knew he was opening his eyes, drool spilling down his parted lips, and above him, someone gasped.

… the smell of blood.

A young girl with dark hair and pink eyes.

Eat.

His fingers twitched, long nails digging on the snow underneath him.

Eat.

"Onii-chan?" the young girl whispered. There were tear stains down her cheeks. He had never seen anyone look so despaired and yet so relieved. He wondered why. He wondered what happened to her. He wondered who she was. He wondered how it would feel to lunge at her frail form right then and there— how it would feel to bite and consume her flesh, feel her warm blood soothe his parched throat. Something about that image felt so right and yet so wrong, his mind fighting against his own body. Eat eat eat eat eat eat— his body was yelling, begging, and he was so hungry, but he doesn't want to, doesn't want to—

"Onii-chan? Can you walk? I can't— I can't carry you, and the snow is so thick, I can't use the cart… if you can't that's alright! I'll run down to the village and get a doctor! You can rest inside for a while… don't die… please hang in there, Onii-chan! I'll save you! I promise I'll save you!"

Onii-chan? he thought. Something you call your older brother. The familiar girl tried to help him up, ushering him from where he was laying down in the cold snow in front of the doorway and inside the small home where the sickly sweet smell was stronger. The girl paled as soon as she opened the dilapidated door, but she steeled herself and guided him inside, and it was then that he saw it, the carnage that was inside of what used to be a quaint little home. Corpses of people strewn about carelessly, their blood seeping through the tatami floor— Mom, Takeo, Hanako, Shigeru, Rokuta— seemingly against his will, his knees crumpled down onto the floor, tears filling his eyes as his throat let out the most agonizing sound…

And it all came rushing back.

His name was Kamado Tanjirou.

"Tanjirou, will you come inside and close the door? The cold is getting in," his mother, Kie, called out to him as she finished laying out their futon in preparation for the night. His younger siblings were already there, all changed into their sleepwear. Shigeru and Hanako were teasing Takeo about something or other, Rokuta was clinging on their mother's yukata as he usually does, but Tanjirou's mind was somewhere else, worrying over where Nezuko was at the moment, especially now that it was getting dark.

"Do you think Nezuko got lost on her way up the mountain? I'm getting worried, maybe I should go down and find her," Tanjirou replied as he followed his mother's orders, closing the door behind him as he walked back inside.

"Nezuko is a sensible girl. I'm sure she's already found somewhere to stay for the night and will be here come morning," Kie replied as she picked Rokuta up, shushing the other children in order to put their baby brother to sleep. "At the very least, I'm sure old man Saburo will not let her climb the mountain in the dark, so rest assured that she will be safe."

Tanjirou hesitated. "But…"

"No 'but's." Kie scolded. "You will stay here for tonight and not wander, alright? Especially with your injured ankle. You are not going anywhere, young man."

Tanjirou smiled sheepishly. It was bad luck, really, that as he was transferring the charcoal into his basket in preparation for his trip down the village, he stumbled and sprained his ankle against a big rock that was buried under the snow. He had tried to hide his injury from everyone, intending to continue on with his trip to sell charcoal so his siblings would be able to have a feast when the New Year arrives, but when Nezuko noticed and asked him seriously if he was feeling alright, she caught him out on his lie. Tanjirou had always been such a bad liar. He couldn't lie to save his life.

Nezuko had sighed and handed him Rokuta right then and there, proposing that they switch chores for the day. Tanjirou would take care of their baby brother and Nezuko would go down the mountain to sell their wares. At first Tanjirou was worried as he didn't want her to get tired, but she insisted that charcoal was relatively lightweight, and sure enough she didn't seem to have any major difficulty with getting the basketful of coal onto her back. He still didn't want her to go, insisting that as the eldest son it was his job to take care of things like this, but his younger sister only laughed and said:

"But I am the eldest daughter of the Kamado family! It's my job to support you whenever I can! Who could we rely on if not each other?"

He couldn't argue with that.

In the end, he bid his sister goodbye as he watched her go down the mountain path on her own. The kids were delighted to find out that they had the whole day to spend with their beloved older brother, and milked it for all its worth. He was not able to help Takeo chop up some firewood because of his injury, but it seemed he was already satisfied with him just being there to talk to. He read some stories to Hanako, promised that he'll get goodies next time he goes to the village to Shigeru, and the next thing he knew the sun was setting on the horizon, pulling the world into darkness, and Nezuko still wasn't home.

He knew his mother was right. Nezuko must be staying over at someone else's house for the night. Their village loved Nezuko, and would not let anything bad happen to her. He was sure she was safe out there, that she will be alright. So why…

Why does the darkness tonight fill him with so much dread?

"Knock knock little bunny from the little mountain… why are your ears so long?" Kie sang, ushering the little ones down onto the futon. Takeo mumbled about not needing any lullaby anymore, but he still snuggled against the covers and closed his eyes. Shigeru and Hanako were giggling softly, and Tanjirou found himself smiling as he sat down beside Kie and reached over to run his fingers through their hair.

"When I was small, my mother ate the leaves of a tall tree and that is why my ears are so long…"

Tanjirou closed his eyes to the soothing voice of his mother, humming along to the tune that Kie had used to sing even when he and Nezuko were little.

"Knock knock little bunny from the little mountain… why are your eyes so red?"

Tanjirou breathed in the scent of happiness and contentment coming off from his siblings and the scent of love from his mother. Even with the feeling of dread lingering in his heart, moments like these comfort him so much.

"When I was small, my mother ate the fruit of a red tree and that is why my eyes are so red..."

The flame of their lamp flickered. Something stank. Something from outside. Tanjirou wrinkled his nose. He couldn't place it, couldn't figure out what it smelled like, just that it was bad. It smelled like… something like—

"Knock knock little bunny from the little mountain…"

— danger.

His eyes shot open, his hand immediately reaching over to grab the hatchet from the corner, standing up as he called out, "Watch out!"

The door exploded inside, as if it was kicked with a great force from the outside. Hanako screamed. Bits and pieces of the wood debris flew towards them from the explosion, and Tanjirou wasted no time to get between the threat and his family, even with the pain that was coming from his injured ankle. Fear gripped his heart as he aimed the hatchet at the person standing in front of their doorway. It was a man wearing a western suit, staring at the family impassively with his piercing red eyes, almost glowing in the lamplight. He didn't look very thrilled to be here, in fact he almost looked bored, at least until his eyes settled on Tanjirou, those red eyes widening a little as he seemed to see something he really, really disliked. Tanjirou felt his heart pounding in his chest, the man smelled like nothing he had ever smelled before. He smelled like pure malice, pure evil, and at that moment Tanjirou was terrified of what he was going to do, terrified that he would not be able to protect his family.

"Those hanafuda earrings… interesting," the man said, almost to himself. "You look so very much like him, it is unsightly..."

"W-Who are you? What are you doing here?!" Tanjirou demanded. The man did not deign to reply. Tanjirou's grip on the hatchet tightened. He wasn't one to attack without provocation, but his nose does not lie. If the man even took one step towards his family, he would not hesitate to fling the hatchet at him with all his might.

It only took a second. The man was absurdly fast. One moment he was standing there at the doorway and then the next he was right in front of Tanjirou, his entire arm punching right through Tanjirou's chest. Tanjirou could not even gasp, he was not sure if his lungs were even functioning anymore, certain that it must have been damaged by the now gaping hole in the middle of his chest. Hanako screamed again as he fell to the ground, coughing up blood, eyes focusing on his mother as he croaked out. "M-Mom… r…. run! RUN!"

The horror in Kie's eyes was palpable, but her determination to get her remaining family away from danger won out. Quickly she was holding up Rokuta who was crying against her chest, yelling at the others to come quick and follow her, but the man was faster. In a single moment he was already in front of her, backhanding her across the face and up towards the ceiling. Rokuta fell on the floor and the man stomped on his little head and crushed him, just like that. Someone was screaming. Tanjirou eventually realized that it was him. Shigeru and Hanako looked terrified out of their wits, but Takeo was quick to take the hatchet that Tanjirou had dropped and yelled at the two younger kids, "You heard Nii-chan! Run!"

With a yell, Takeo charged towards the man, who at this point could not possibly be human. With all his strength he cleaved the hatchet onto the man's back, but all it did was damage his clothes, and the force did not even seem enough to dig into his skin. Takeo gasped, and the next moment, the man had his hand around the young boy's throat, lifting him effortlessly as he crushed his windpipe. Tanjirou could not take his eyes away as the man tossed Takeo's body like it was a rag doll. Takeo hit the wall with a loud thud, his blood spraying all over the wall. Shigeru and Hanako were against another wall, shivering in terror, and Tanjirou pleaded for them to run, please please please run— but at this point even he didn't think it would matter. The man was simply too fast. With barely even an effort he killed his two remaining siblings as well, Hanako with a kick and Shigeru with a hand through his heart, and Tanjirou screamed as much as he could scream with his weakening body, knowing that he too was going to die soon, hearing his own heartbeat wane inside his ears, anger and terror brimming inside his dying heart.

The man did not even seem perturbed, nor did he seem to break a sweat. He just looked at the carnage he had caused on the slaughtered family and turned on his feet, walking out of the house. Tanjirou wasn't about to let him get away. Ignoring all the pain he felt, he crawled over from the tatami floor and into the cold snow outside, grabbing the man's ankle, looking up at him with rage-filled eyes, yelling at the top of his lungs even as blood gurgled from his throat.

"You… monster! You won't…. get away with this…! I'll hunt you down and end you… even from beyond the grave!"

To his immense frustration, the man did not even look threatened. In fact, he looked mildly amused. Tanjirou supposed it was hard to feel threatened when the one doing the threatening was so clearly already on death's door. The man crouched down to meet him eye to eye, eyes flickering momentarily at the hanafuda earrings he had mentioned earlier, murmuring once more to himself.

"A descendant of the sun-breathers… surely would have a chance to defeat the sun someday." He lifted a single finger, the nail on his fingertip turning blue and lengthening in front of Tanjirou's eyes. Tanjirou met the man's slitted red eyes and thought he saw a hunger there, filled with wanting and greed. "Why don't we try those words of yours, little sun-breather? Would you still thirst for revenge when you've become the very being you despise? Would you even remember? I wonder."

Tanjirou coughed out more blood, his fingers on the man's ankle weakening, his eyesight faltering and blurring out.

"I'm getting ahead of myself. There is a chance you may not even survive the transformation… perhaps it would not matter."

He felt a stabbing pain against his forehead, a pinprick compared to the agony that was going on in his gaping chest. The tiny pain did not last though. Instead it started to burn, hotter and hotter, until Tanjirou was screaming himself hoarse, convulsing against the cold snow as his skin felt like it was being flayed over hot coals and torn apart over and over. It was beyond torture, beyond pain. He gasped until he can't gasp anymore, screamed until he could not scream anymore. Above him, he heard chuckling. The man was dusting off his clothes and watching. Tanjirou would not forgive him. Tanjirou would never forgive him.

"I'll leave the corpses as a present for you. You'll have quite the feast. I'm quite generous, aren't I?"

Never… ever! Never forgive!

Tanjirou forced his eyes open, committing the man's visage to memory, inhaling to remember his scent. Something tells him he would not die tonight. Something was happening to his body. Something that was not necessarily a good thing, but one thing was for sure: he would never forget this man for as long as he lived, would never be satisfied until he had torn him apart with his bare hands. This rage was scary. Tanjirou had never been this angry his entire life. It felt suffocating, like he would lose his entire self in it, and Tanjirou was not sure what was waiting for him on the other side.

Never…

As he lost consciousness, a fleeting thought echoed in his head. A small bit of solace after a night of tragedy. At the very least, there was a single person he had not lost, a single person who was not here to see this nightmare unfold.

Nezuko was safe. He had not lost his entire family. Nezuko was safe.

And as he closed his eyes and let the darkness consume him, that was all that mattered.

Taisho Secret: Like in canon, it was old man Saburo who kept Nezuko from going back up the mountain in the middle of the night. Unfortunately, one unlucky fellow got beat up pretty badly and accused because of a plate that a cat broke. Nezuko wasn't able to help him.