126 years ago …

There was little that could surprise Muzan Kibutsuji. He considered himself supremely knowledgeable in many fields and with a razor sharp intelligence to pair with it, his predictions were often right.

He'd lived dozens of those measly human's lifecycles and had met many people. He'd allowed those who feared him to follow, and those who hated him found death at the hands of his servants.

The only thing he feared was the sun, he hated the primal terror that he'd felt each time a ray got near him. He was the pinnacle of evolution, but half the day was snatched from his claws.

His impatience with his treatments had cost him dearly, in retrospect he wished he'd kept the doctor alive for a little bit longer. But, he couldn't afford to dwell on the past. He could win with the pieces he found along the way.

He was traveling north of Kyoto when he heard it.

A sound like none he'd heard before. The only way he could verbalize it was if thousands of different types of papers were being ripped, while water boiled and fire raged. If lightning was striking and a bullfrog croaking.

It was inhuman. More than inhuman it was an inconceivable, twisted sound that would haunt his memory.

As if his feet had a mind of their own, he raced along the puddle marked path, leaping forward. As he approached, the smell of ozone, pine, and blood assaulted his nostrils. He took another whiff when a sound called from further into the forest.

"Y-yukino…" A male voice painfully croaked out.

Muzan tutted before moving forward, there was a young human male impaled by a palm tree. His eyes widened.

He didn't care about the grisly sight before him, he'd seen worse, he'd done worse, and he'd enjoyed worse.

But there was no sign of how the man found himself impaled by the tree. To do so someone would've had to have thrown him at massive speeds. But none of the other surrounding trees were damaged, nor was his position consistent with falling from a height.

Even more bizarrely, the tree didn't appear damaged. None of the branches were so much as bent. From all appearances it seemed like the tree had grown through the boy.

Hikigaya stared out at the cursed green forest around him with his single intact eye. Even thinking was agony, but he needed to find Yukino. He wanted her to be okay. He needed her to be okay. Even if he wasn't going to make it.

She could do the things that needed to be done if he died. Yukino would know what to say to Komachi and how to console his mother. She would give proper final regards from him to Yui, Totsuka, Zaimokuza, and Kawa-something.

He couldn't speak, one of the branches had pierced directly through his throat. But when the well dressed man appeared, he tried. All that came out was a disgustingly wet gurgle more animal than human.

As one black eye scrunched in pain met the reptilian slits of the first demon, Muzan smiled. The boy had something that would make him a worthy demon. The will to survive.

Muzan had never accepted that he'd die, neither did Hikigaya accept his own death.

Kibutsuji slashed his left palm with one of long sharp fingernails on his right hand. He dropped the blood onto the boys gouged eye socket.

Hikigaya shrieked in agony. His tongue was destroyed and his voice box pierced but his screams of distress were only more guttural because of it.

Hachiman thrashed within his needle filled constraints. The changes his body was outgoing far outstripped the pain of being impaled.

Snap!

His left femur broke itself and began to regenerate stronger and more durable than before.

Crackle!

The branch impaling his stomach began to disintegrate from the sheer force he writhed with.

Pop!

His back arched as every muscle tensed, stronger than ever before. It came to a point where he could arch no more. His spine was right on the threshold but his body had a mind of its own. He flexed further and his spine broke.

He could feel the vertebrae fire off into his body.

Kibutsuji smiled at the scene before walking away.

He'd sated his curiosity and sadism; at least for the moment. He had things to do.

He wondered if he would ever see that demon again.

~/~

Two hours after Hachiman was transformed …

Hungry. So hungry.

Like Sisyphus. How'd Hikigaya know that name? Was he Hikigaya? He didn't know.

He knew he was hungry and needed to eat. He scuttled toward the edge of the town on all fours like a beast, drool dropped from his gaping maw. He was so hungry.

There was people here. They had food. They were food. All people could be food. He wanted to eat food.

He was going to eat them.

The last thing this animalistic beast cared for was subtlety or stealth. He used his newly found strength to crash through a random family's front door and charge into their bedroom.

He ripped them apart piece by piece, and fed on everything inside of them. Like when Yukino and he had eaten oysters for their second anniversary.

Slurping and chewing, biting and tearing. Hikigaya ate and ate. They screamed and tried to run, but he was too fast. He chased the runners and saved the people frozen in terror for last.

By the time that he returned to his senses. The street lay littered with the exsanguinated bodies of his victims. In the center of the small town's square, lay a dead girl. Still clutching her doll to her chest.

He slowly stepped towards her while avoiding the other corpses. The horror of what he'd done sinking in. He fell to his knees and clutched her small body to his bare chest. "I'm sorry. I'm sorry. I'm sorry. I didn't know. I'm sorry. I didn't mean to. It was my fault. I'm sorry. I didn't want to- please rest in peace."

He screamed skyward.

Hikigaya didn't know how long he stayed with the body. All he knew was that the only reason he moved from his spot was the sun's scorching rays peaking over the East mountain bordering the village. Hikigaya lay her body down and hurried into the nearest house. He shut the blinds and went into a west facing room. Avoiding the danger.

In the blood stained room was the corpse of a middle aged man, his jaw ripped so wide open that he looked like a snake.

Hikigaya clasped a hand over his hand to keep from screaming and instead dragged the man into another room. He couldn't bear to look at the corpse for a moment longer.

To see the echoes of fear on the dead man's face. That man's last few moments had been agony and terror, that was how he died. That was how Hikigaya had killed him.

He didn't know what came over him. He didn't think he wanted to know how the rest of these people had died.

Hikigaya tucked himself into the family's large wooden dresser, ignoring the blood spatter atop its doors. He closed his eyes and tried to think of anything but the massacre.

His mind was filled with thoughts of Yukino. Dreams about the ring that he had hidden in the back of his sock drawer. Of how surprised he'd been when she told him she wanted him to propose to her, or she'd propose to him instead.

Small tears trailed down his cheeks as he sniffled. He muffled the cries and closed his eyes. Hoping beyond hope that he would open his eyes later and find that this had all been one horrible dream.

When his eyes did open, the sun was beginning to set and he had hardened his resolve. He didn't know what the hell was going on but there had to be a way to get back to Yukino. He just needed to find it.

He turned his focus inwards. From the blood coursing through his veins there was certain things he knew to be indubitably true; he hadn't the foggiest idea of how he knew, but the information was ingrained. The sunlight would kill him. He fed on humans, and only humans. Finally, he'd been created by Muzan Kibutsuji but his name should never be said aloud.

First things first however. He needed to get out of here. This was a relatively small and isolated town, and Hikigaya was certain that he'd killed every resident; but, when over two-hundred people aren't conducting business, someone's bound to notice.

How long would it be before a traveling trader or a concerned relative traversed the path and found the massacre. Hikigaya stood to leave. He was clad in a eviscerated pair of jeans that he stripped out of and traded for a traditional set of robes that peasant farmers commonly wore. The dead had no use for possessions.

He began to make his way out of town but stopped as he passed the corpse of the girl with the doll. Hikigaya sighed and then spat a curse. But turned back and began to drag the bodies toward the town square.

His new found strength let him carry them easily, his only limiter now being the number of corpses that he could wrap his arms around. He was sure that he could hurl them and expedite the process but decided against it. He still had some shame however, he'd fallen low; but not so low as to treat his victim's bodies like rag dolls.

He piled them like the world's most morbid game of Jenga. Once all 247 bodies were stacked together. He kicked in the door to the village store room and grabbed the barrels of whale oil he assumed were meant to last their lanterns through the winter.

Speaking of winter, what season was it? What time period was it? Was he even still in Japan?

He shooed the intrusive thoughts away from his mind and rolled all five barrels towards the town center at once. Using his now powerful limbs to shepherd them. He pushed the barrels atop the pile and then punched into them near the bottom. Letting the flammable liquid leak out onto the bodies. He took a flint he'd found on a paupers bedside table and struck it.

The single spark was just enough to start the fire. Before long the small blaze had grown to a roaring inferno, all the bodies burning simultaneously.

Hikigaya sniffed the air. He chuckled grimly. He wasn't sure what he'd been expecting, maybe a barbecue-esque scent but what he got was every disgusting burnt scent in a medley along with what smelled like burning meat.

Burnt hair. Burnt shit. Burnt people.

It was disgusting and he turned away sooner rather than later.

With the morbid task done, he turned and walked away from the village. A black traveler's cloak hiding all of him from view.

~/~

Present …

Tanjiro woke up to several beautiful girls standing over him. They talked in increasingly agitated tones.

Their voices carried slightly but the echo of the wooden room was dampened significantly by the partition curtains on each side of the bed. Massive windows let in natural light and made the room feel bigger.

Each bed was uniform and pristine, folded white linen tucked crisply underneath the mattress. The curtains were a soft purple that dampened the harsh sunlight without being suffocating. Overall the room was quite pleasant, Tanjiro thought. Though a strong alcoholic stench seemed to permeate the walls of this place.

The shortest one spoke first. "I'll handle the pervert."

The one with pigtails chuckled. "Make sure that he can still walk after. Kanao you'll be handling mr eavesdropper here."

The one with a side ponytail, smiled blankly and looked at Tanjiro. He grinned back bashfully, he'd never spent significant time with any women whom he wasn't related to. Always too busy training and before that working.

The tall slender one sighed. "I guess that I'll take the feral one."

His examiners drifted away except for the one with the pigtails. "Head downstairs and find Kanao after you get up she'll help with your rehabilitation training." She turned away briskly and began to wash something in the small sink nearby.

"It was nice to meet you, I'm Tanjiro." He called out at her retreating back. She stopped and stiffened.

"Aoi." She continued on her way like nothing had happened.

Tanjiro smiled, he hoped that they could be friends.

~/~

Inosuke didn't like his instructor. She was too prim and proper for him to get along with. Worse though she maintained the perfectly infuriating amount of condescension.

She fit perfectly with the white walls of the dojo and the cleanly manicured lawn, he did not. His boar head stuck out like a sore thumb and his voice wasn't used to the low tones people spoke with here. He didn't like this place, not at all.

Inosuke was only here because of his loyalty to Gonpachiro and his demonic little sister.

"Truly, is this all that you're capable of? Although you were a junior slayer, I expected at least some degree of competency." Yukino danced away from him as he lost once more in their game of pursuit. Her breath barely even strained.

She'd found him too hyperactive to train with the cup game so had immediately launched them into a lightning fast game of tag.

She gracefully glided back and forth. Steps light and measured. Each movement of hers was practiced to perfection.

Inosuke moved like a beast. All intuition and adaptability. At times he managed to surprise her and move in a way that she wasn't expecting but it never led to a touch. She was just too experienced.

The most humiliating part of it all was that she wasn't leveraging her superior speed. She moved at his pace to keep the exercise engaging. Yukino beat him with skill. Using flexibility and eleganct dodges to stay a step ahead of him.

When they stopped for lunch he was almost snarling in frustration. Yukinoshita spoke first. "You're very talented but you need to train more. Have you ever heard of total concentration constant?"

The boar head cocked to one side and she took that as a no.

"It's a breathing technique where you learn to maintain total concentration indefinitely. It's what separates elite demon slayers from the riff-raff." She explained without any disrespect laced in her velvet tones. Yukino did genuinely enjoy teaching. She'd wanted to be a professor before she'd been ripped across time and space.

Yukino had a domestic fantasy that she'd nursed since she was a third year in high school. Of her coming home after a long day teaching, Hachiman would be working from home on his latest novel or article as the children played outside in their small but well-tended garden.

She would greet her husband with a kiss and sniff the air to see what he had cooking. She'd take a bath and then the whole family would eat together. Yukino wanted a boy and a girl, who she could teach table manners to and listen as they rambled about their day.

She wanted to share a glass of wine with the love of her life after the children were put to bed and share in the intimacy of being close. She had imagined grading papers as her husband read, or of passionate evenings with their bedroom door locked.

Yukino wanted to hold her man close under the covers, as the heavens fiercely poured rain over their cozy home. She'd had a ring picked and had told Hachiman that she wanted to propose to him.

Then as slowly as their love had grown, they'd just as suddenly been ripped apart by the cruel machinations of fate.

She was cut out of her melancholic fantasies as Inosuke grumbled excitedly.

"Teach me how to do it. How do I learn?" He dashed toward her and pushed the snout directly into her face.

"Take a step back and then we shall begin. Enter your total concentration form and now maintain it."

"I'll get it done." He shouted exuberantly.

~/~

Zenitsu tried to sneak another peak at Shinobu as she pressed one foot down into the small of his back. "Stretch farther."

"That's as far as I go." His breath came out in a pained rasp.

"Not. Good. Enough!" She pushed with more force than her seemingly waiting body should've allowed. And Zenitsu managed to stretch a few inches farther than he had before.

Shinobu kept pushing for another minute as they gained him painstaking millimeters of mobility. The short girl only relented when the melodic ringing of a bell swept through the estate.

"Well, that's the call for dinner time." Shinobu kept him down with her foot as he tried to rise. "Either you stay here with me or you go and drink all of your spider medicine first. Am I understood?"

The pressure from her leg didn't dissipate until he'd nodded his agreement to her. "I'll drink my medicine just please let me go." He begged.

She nodded her approval and stepped back. Zenitsu rushed out the dojo door before she had the chance to change her mind.

Along the way he crossed paths with Inosuke and Yukinoshita. The two quietly made their way towards the dining room as the boar-headed youth huffed and puffed.

Zenitsu examined the volatile boy with a modicum of concern which Yukino waved off. "Don't worry about him, he's just practicing a new breathing technique. We'll meet you at the dining hall."

Yukino looked as prim as she had in the morning while Inosuke's bare skin was streaked with dirt and runners of sweat. Her blue eyes had an efficient gleam in them that Zenitsu really didn't want to test.

He moved further down the hall and ran next into a limping Tanjiro who reeked of green tea. Kanao walked beside him with the same apathetic smile that she always carried.

Tanjiro's white rehab pajamas were stained green. Kanao's hair looked only slightly mussed.

Zenitsu entered the dining room and at the head of the table, sat one of the most beautiful women that he'd ever seen. She had the same butterfly pins in her hair as Shinobu, Aoi, and Kanao. She smiled at Zenitsu in a way that made his knees weak. "Oh, you must Zenitsu. I'm Kanae Koucho, it's great to meet you."

She tilted her head when he didn't reply. Zenitsu racked his brains for something to reply with. Some way to not embarrass himself in front of maybe the most beautiful girl he'd ever even heard of. "Hi, I'm Zenitsu. You have a lively home, I mean you have a lovely home."

She giggled. "Thank you, I'd agree with both compliments. Though I must confess that my duties as a pillar call me away so often that I hardly tend to the estate. But, the kind words are appreciated and I'll extend the praise to my little sisters."

He nodded dumbly and hovered in the door frame. He only moved when a smaller body bumped into him. "Move dummy." Shinobu frowned at the younger male as Kanae gently chided her little sister. "Shinobu, be nice. It's his first time meeting a pillar."

Kanae focused on him once more. "Don't worry, Zenitsu. We're not as scary as people say. I know how the mizunoe talk, they say we're these 'big scary pillars' who are violent and angry. Most of us are pretty normal." She winked, Zenitsu blushed. "Besides, he was just talking about how beautiful the butterfly estate is. That's praise for your work."

Shinobu huffed, but a small smile wormed its way onto her face. "Good. I'm glad somebody can appreciate it." She sat at her big sisters left hand.

Zenitsu sat on Kanae's right. As the two other pairs came in. They seemed to follow the same pattern. Tanjiro sat next to Zenitsu and Kanao kneeled next to Shinobu.

Inosuke trudged in and sat next to Tanjiro while Yukino danced in like it had been pre-choreographed before sitting next to Kanao.

Finally bringing up the rear was Aoi, who kneeled at the foot of the table. "Sorry, I had to do a small surgery." Zenitsu could hear the tremor in her voice as she spoke.

"That was brave of you Aoi." Kanae smiled like a proud mother. Aoi flushed and averted her eyes.

The girls - Naho, Kiyo, and Sumi - brought out several dishes before plopping them down between various people. One of the grils sat with Kanae, another with Kanao, and the third by Aoi.

They ate quietly until Kanae asked for an update on the boys' progress.

Kanao smiled and didn't react, Kanae's smile dimmed and Tanjiro jumped in to ease the awkwardness. "We're doing the cup training right now. Kanao is super-fast but I feel like I'm learning a lot."

Kanae smiled before looking at Shinobu. Shinobu straightened slightly and took on a more professional demeanor. "My patient is approximately two-thirds of the way recovered in terms of acceptable mobility and tissue strength. He should have full range of motion by the end of the week."

Kanae nodded, less motherly and more like that of a superior. Shinobu appreciated the acknowledgment of her expertise and skill. "That's good, what about strength and stamina?"

"I can rehabilitate him to acceptable levels within three weeks."

Kanae allowed a smile to work its way onto her face and turned to Yukinoshita.

Yukinoshita cleared her throat and spoke at a moderate volume, her tone refined and a strange brand of exotic. "I deem Inosuke fit for full training. I started to teach him the foundations of total concentration - constant."

Kanae tilted an eyebrow.

Yukino rushed to explain, a small flush coloring her cheeks. "I apologize, I acted in a way that I thought was best. He seemed healthy so I tried to … well I should've asked for permission-"

She was cut off by soft giggles from Kanae. "Oh, Yukino. Never change. You're doing a wonderful job, thank you for helping us out."

The snow tsugoku pouted slightly. Pointedly looking away while aggravatedly eating her rice.

Tanjiro piped up. "What's total concentration constant?"

Shinobu answered. "It's the technique that allows you to get stronger by making total concentration levels your baseline. So each breath technique after is more dangerous because your body can focus more on that rather than maintaining total concentration. All the hashira and high-ranked slayers can do it." She smiled softly with a small dose of smug self-confidence.

"Wow, that's amazing. So you're all doing total concentration right now?" Tanjiro looked around the table excitedly but saw awkward expressions on four of the women while Aoi looked away awkwardly, her hands clenched into fists.

No one said anything but surprisingly it was Inosuke who saved the conversation. He looked at Aoi's turned-away face. "She saves pillars so if anything she's got more demon kills than anyone."

Kanae's soft frown morphed back into her usual smile. "What a wonderful way to put it Inosuke?"

The boy shrugged and returned to his food.

~/~

The days went by faster than expected. Zenitsu recovered fully and began training total concentration - constant with Tanjiro and Inosuke. He complained all the while.

Inosuke noticed that he was getting faster and stronger. The training was paying off. They shared more meals at the butterfly estate but Kanae was gone more often than present.

Yukinoshita and Shinobu were absent at least twice a week. The duties of being a high ranked demon slayer seemed ceaseless.

Six weeks passed and all the boys felt stronger than before. Inosuke adapted his newfound athleticism into his already unpredictable style and had been experimenting with techniques on Zenitsu.

He'd gotten so far that he even managed to surprise Yukino in a spar. She rolled away from his follow-up and that was when her locket came loose.

Inosuke didn't notice at first, too caught up in the fight. But when she had him at sword point, he glanced down and it was open, inside was a small sketch of a squinty-eyed man with sharp features.

Yukinoshita followed his gaze and her left arm shot up and closed the locket, before tucking it away. The ice in her gaze promised pain if he asked.

Inosuke shrugged, he wasn't a genius but he had a good guess of who that man was to her and why she joined the corps. No need to risk a beat down for a story he'd heard before.

He turned away and Yukinoshita took a moment to press her hand into her shirt and hold the locket to her heart.