Prologue: Mercy

Japan has always been a land of countless stories and legends. Tales of yokai that trick men, women, and children for play or for malice, whispers of oni that come in the night to feast on the flesh of the unsuspecting. Stories of gods and demons, of spirits and sages, and of immortals and monsters.

Some of those tales are pure fantasy, some hold grains of truth, and still others are almost completely accurate.

This is a tale of demons, and those who slay them. A tale of immortals, and the cost of their lives. A tale of a legacy, a name, and a Fang to be bared against the howling dark.

This is the tale of the man once known as Sekiro, the One Armed Wolf, and of the boy who would become his disciple.

-x-x-x-x-x-

The noise of metal scraping against wood echoed through the night, filling a small patch of woods surrounding a dilapidated temple with its quiet, rhythmic cadence. Most nights, the only beings present to hear the noise were the various animals that lived on Mt. Hiei.

However, this was not most nights.

Usually, demons avoided Mt. Hiei almost instinctively. However, through a mix of greed and reckless confidence, the demon named Kiba managed to ignore the deep, pervading unease oozing through his being and climb the mountain.

Pale skin seemed to almost shimmer under the moonlight, and long tresses of blond hair blew in the faint breeze as Kiba ascended.

'All those superstitious fools think that there's some kind of spirit up here; I bet those Demon Slayers hid something up there that they don't want His Excellency to find!' Kiba let out a low chuckle, the sound like stones clacking together. 'If I bring it to him, I'm sure to receive his favor!' He flexed his fingers with barely restrained glee. 'Twelve Demon Moons, here I come!'

In the next instant he was gone, a faint puff of displaced air and dust the only indication that anyone had been there in the first place.

Swiftly and silently did he ascend the mountain. No leaf was left disturbed in his wake, no branch was left broken, no sleeping bird was woken. For in truth, Kiba was bare inches beneath the weakest of the Twelve Demon Moons; membership of Muzan Kibutsuji's elite was nearly within his grasp even without this attempt to curry favor.

After all, Kiba wasn't just powerful, he was clever. He picked his prey carefully and never stayed in one place for too long. Never hunted the same kind of prey for too long. And most importantly, he never fought fair.

Had Kiba been right, had this been a secret hideaway of the Ubayashiki legacy, he likely would've been offered the opportunity to slay the bearer of the Lower Moon Six title and take his place.

Unfortunately for Kiba, he couldn't have been more wrong. Perhaps he'd let his power go to his head, perhaps he'd accumulated enough bad karma as a demon to attract the gaze of a vengeful spirit, perhaps it was simply bad luck. Who could say? All that mattered was that he chose poorly...not that he knew it yet.

After about a minute, Kiba paused in his ascent and cocked his head. His demonically enhanced hearing could just barely make out a faint scraping sound, one he recognized. In his human life, Kiba had been married to a wood carver, a kind woman who made her living creating statues and charms for tourists.

Of course, Kiba didn't really remember much of this, due to the demonic blood coursing through him. All the same, a faint flicker of memory surfaced just long enough for him to recognize the sound of wood being carved.

'Hmm, climbing is hungry work. It couldn't hurt to stop for a snack. Plus, sunrise should be soon; might as well kill two humans with one stone.'

An inhumanly wide grin split Kiba's face, revealing fangs far too long to fit in the mouth of any human. He flexed his fingers again, and a pair of thin, flat bones erupted from his palms, continuing to grow until they were each about a meter in length. He wrapped his fingers around the blades, the bone molding to his grip perfectly.

He darted through the trees silently, his blades held low to his sides as he ran, until abruptly he emerged from the trees. Before him stood a small, dilapidated temple. Hell, it barely qualified as a temple; it looked more like a live-in shrine, really. Of more note was the absolutely staggering number of hand-carved Buddha statues that surrounded the building in ever-widening, concentric circles. The only part of the clearing that was bare of statues was the path up to the entrance of the shrine.

However, Kiba's mind was not on the pitiable state of the grounds, or the innumerable host of carven offerings. No, there was but one thing occupying his mind, one sole sensation consuming the very fiber of his reason.

The smell of blood.

The blood was old, very old. The kind of faint iron tinge that would linger in a clinic or a morgue; the scent of an old wound. Normally, such a scent wouldn't have much of an effect on a demon as old as Kiba.

But this was not normal blood.

Drool poured from the corners of Kiba's mouth like a waterfall. In that moment, nothing else mattered. Power, Muzan's favor, even his own life; all were forgotten in the face of an overwhelming, ravenous hunger. If he couldn't drink every last drop of that heavenly ichor, he would die.

Kiba charged into the temple, not noticing that the sounds of carving coming from within had stopped.

Then, all was silent.

-x-x-x-

The man who had, many eras past, been given the name "Sekiro" set the small, bloodstained carving knife down and turned to regard the severed head on the steps of his retreat. The severed head that was even now snarling at him, trying in vain to command its body to strike him down. Fortunately, the kick that had followed his decapitating blow had sent the demon's body flying across the clearing to be impaled through the torso on a broken tree branch.

Time truly had not been kind to him, Wolf reflected as he absently brushed at the tattered rags he wore. A cut that would have once been so clean that no blood would have touched the blade was instead a jagged, cruel wound unbefitting of the skills pounded into his flesh by Owl, and the monks of Senpou Temple would have wept in shame at the inefficiency of his followup, were they still around in this era.

Three centuries with few opponents, and none of a level that could challenge him, had left him lacking a means of honing his skills. Wolf gazed at the demon that had made its way into his home. This one was the strongest yet, and even he had been dispatched with ease. A hand that had no right to be as youthful as it was dipped into a weathered satchel and came out with a small clump of thin, pink, faintly glowing pieces of paper.

As Wolf sprinkled the divine confetti onto the snarling demon head, he closed his eyes and quietly offered a prayer.

"May you find in your next life the peace that was stolen from you in this one."

As pink flames consumed the head and body of the demon that was once Kiba Himeji, he felt no pain. A tear escaped his eye, going untouched by the divine flame as it burned away the corruption gnawing at the roots of his soul.

'Akano...forgive me, my love.'

Whether the vision of his wife that appeared before him was merely a construct of his dying mind or was him seeing into the Pure World, none could say. But as he died, as the blessed flames freed the surviving shards of his human soul from Muzan's cursed blood, Kiba Himeji knew peace.

For a time, Wolf simply stood there in the door of his temple, breathing in the night air. A burning sensation in the stump of his left arm brought him back to his senses, and he retreated back inside.

As the first rays of the sun's light peeked through the trees, the sound of wood being carved could be heard once more.

-x-x-x-x-x-

Kiyoshi was cold. It seemed there wasn't the slightest flicker of warmth in his entire body...but even against that frigid backdrop he could feel an endless, vicious cold creeping up his arm, robbing him of all of his senses save one. How could this happen? It was like a nightmare…

That man...like it was nothing to him, he had killed Kiyoshi's mother and devoured her in front of the boy's eyes. There had been no blood, oddly. No viscera stained the fine wooden floors of the room, not a single scrap of human flesh remained to taint the mountain of fluffy pillows the smiling man reclined on.

Even as frozen evil cut open a gash in his hand, Kiyoshi's sight vanished, leaving behind a faint afterimage of the lavish shrine they'd been called into.

His sense of smell and taste were the next to go, tearing from him the bitter scent of incense and the flavor of the pork bun the man had given him, which had already become as ash in his mouth.

When the ice began creeping through his veins so too did his sense of touch fade, though the all-consuming cold remained.

Finally, his hearing was stolen. No more could he hear the sutras from the monks that lived here in this serpent's den, nor could he hear the fervent prayers of those enamored with this man's false glory. The last thing he heard was the man—no, the monster whisper five words to him.

Thank me if you survive.

But nothing that the demon could do to him could steal his final, sixth sense. His mother's family, the Ametsuchi clan, had in the past been a clan of sorcerers and spiritualists, of monks and mediums. But in the modern era, their services had become less and less wanted, and the once-great clan fell to obscurity.

And now… Now Kiyoshi was the only Ametsuchi left alive, and quite possibly the only person left in the world able to sense Chi.

(This assumption was far from the case, in truth, but Kiyoshi had no way of knowing this at the time.)

Kiyoshi had met many people in the years he and his mother traveled, and had learned to "close" his inner eye; even petty grudges made a person's Chi uncomfortable to sense, to say nothing of actual hatred. But now he was wishing he'd toughened up and tried to get used to the discomfort, because if he had, if he made a practice of keeping that eye open…

He'd have never let his mother come within a mile of this abomination.

Looking at the monster's aura was like being caught in a blizzard made of frozen acid. It was a thousand times worse than the ice creeping up his arm. Mercifully though, he soon fell unconscious, his young body and mind unable to cope with all the abuse that had been heaped onto them.

-x-x-x-

The first thing Kiyoshi noticed when he woke up was that he could feel again. The second thing he noticed was the pain. It was a dull, throbbing ache in his lower arm, a far cry from the icy agony that had been creeping up the limb before. He shifted in the futon—

'Futon?'

That was when he noticed the third thing. As he cast about himself in confusion, he took in the room. It was sparse, almost bare, with but one sliding door and little furnishing beyond the futon he laid in and a small chest of drawers in a corner. Yet, in spite of its smallness, there remained an aura of care, of warmth about it. A far cry from the lavish room that they—

Kiyoshi froze, memories coming back like a clap of thunder.

Indeed, he was no longer in the shrine where he and his mother had stopped to rest for the night. No longer at that place where his mother had been...had been...!

He began to hyperventilate, a brick of panic and grief pressing down on his chest as he struggled to sit up. A brick that only grew heavier when he tried to feel around him with his left hand, only for him to touch nothing, to feel nothing from that hand. He looked down at his hand, and saw empty space where it should have been.

Kiyoshi screamed. It took minutes for his voice to give out, and all that was left afterward was silence and tears.

-x-x-x-x-x-

Yes, indeed. This tale will be one fraught with sorrow and loss, of pain and fear. But so too will it be a tale of hope and determination, of strength both outer and inner, of outlasting the dark to reach the dawn. A tale of demons, and those who give them the only mercy they can. A tale of a sculptor and a doctor, both so very tired in their age, but who continue on nonetheless. A tale of a boy, orphaned by a demon, raised by a sculptor, trained as a shinobi and called to be a Slayer of Demons.

This is the tale of the boy who would be known as Sekiko, the One Armed Fox, and the path he shall take through this era.

AN: Another day, another plotbunny. I watched Kimetsu no Yaiba and fell in love instantly, and once I binged the manga, I knew I had to cross it with Sekiro. This is the result. I hope you all enjoy!