Disclaimer: I do not own Sekiro: Shadows Die Twice nor do I own Demon Slayer: Kimetsu no Yaiba. Credit for the cover page goes to tatsuya (pixiv id: 418816).

A/N: I have a question. Why is it that no one, except for two other people (as of writing this note), thought it'd be a good idea to write a Sekiro x Demon Slayer X-over? I'm genuinely curious. It's been a year since the game was released and only two have been made, and there are so many things the two have in common:


-Breathing styles/techniques (minor, but it's there)

-Demons (and to an extent, Shura)

-A relatively dark atmosphere

-A supernatural theme

And then some. The two were practically made for each other! Granted, one of the two other Sekiro X-overs is a oneshot but that's neither here nor there.

Ah well. Here's my take, I suppose. Or rather, this is my tribute to Sekiro's incoming 1st anniversary.

The Root: PT 1

It had only been a passing rumor, but for him, it could not be ignored.

The Demon in man's flesh observed the wartorn panorama that was once the thriving lands of the Ashina clan. He watched the red warriors of the Interior Ministry – samurais of the Tokugawa Shogunate – cut down the remnants of Ashina's own, who amounted to no more than ailing old men, wounded soldiers, and inexperienced ashigaru's barely fresh out of training. Famed resilience or not, Ashina could still succumb to numbers. Quantity over quality and Tokugawa had quantity. He would ask where the fit and strong ones of Ashina were, but one of his position could care less about them.

Then… he turned his attention to the Demon that was wildly wrecking the outskirts in front of Ashina's castle gates, massacring contingents after contingents of Tokugawa's warriors without care. In a feat that was completely unlike him, the Demon took some time to marvel at the sight, amused and almost awed by what he was witnessing.

So much Bloodlust.

So much Hatred.

So much Resentment.

Not once did the Flames of Wrath that it swathed abate, only consuming everything it touched. The screams emanating from those exposed to it were nothing more than cathartic. He had yet to realize the karmic debt accrued by the one who would come to be known as the Demon of Hatred. For now, he only knew that aside from ingesting his own revered blood, there were other ways for mortals to become a Demon.

…He would have to return to that Demon later.

A faint whisper of a distant memory he had long forgotten flowed through his many brains. He struggled for a moment to make sense of why he was recalling it now… then it hit him. One particular person crossed his mind which made him remember why he had not thought of entering Ashina until now.

Ashina Isshin.

The Demon had once approached that human in an attempt to turn him over as he had with the brother of Yoriichi – now named Kokushibou – who had information on other human warriors that were potential threats to Demons and was responsible for letting him know about Isshin in the first place.

The withered old human had simply laughed, called him a likeness of "Shura", and sliced him down without him knowing.

Then slashed him.

Then stabbed him.

And administered all manners of killing that could be done by the sword.

It did not matter to Isshin what form the Demon took, whether it be a monstrous behemoth with countless limbs, or a multitude of skulking, venomous snakes agile in their slithers, he sliced him with punity, almost as if he knew exactly where all of his hearts and brains were. And, knowing that he could not kill him, he made do with making a mockery of him instead by slashing him apart countless times, even using his own Blood Demon Art against him at one point, until the sun rose.

Isshin was not a Demon Slayer. He was a Sword. He was utterly unpleasant and Muzan had no desire to be in his presence again after that disgraceful night. He did not need anything or anyone that could mock his authority.

It finally made sense why he stepped into Ashina after so long. Isshin had passed away. The clan was no longer in its Golden Age. The Tokugawa shogunate had immediately assaulted the land in force upon news of Isshin's death and made quick work of its remaining forces.

Which led to now.

Normally, he would ignore rumors conjured up by humans and demons not even worth his attention or even acknowledgment. After all, why should he care for their existence? The only thing that was worthy of being acknowledged was he and himself only.

But this rumor… it was too much of a coincidence to be dismissed…

The land that attracted the gods' attention, Ashina was called. Specifically, it was only a small patch of land within the Ashina's land, but supposedly there laid the very materials that were sought by many who pursued longevity and immortality. That had warranted the attention of the Interior Ministry who wanted them for themselves. For him, however, such a description could be the residence of the very thing he desired for so many centuries.

The Blue Spider Lily.

Eventually, he compromised with himself.

It was only a rumor and nothing more or less, but there was still much to do in such a place. The doctor that administered that treatment so long ago, back in the Heian period, could not have been in a single place all the time. He had to have gone to many places to acquire the skills and materials to turn one like himself into the progenitor of all Demons. It had almost been a millennium since and still, nothing came across the many eyes he had scattered across all of Japan. He was becoming impatient and disappointed in the ones he created, so having something to do may ease his mind even a little.

It did not hurt that there could be some who were resentful enough for him to convince into becoming powerful Demons. And the more Demons for him to take advantage of, the better.

And so, with a smile full of promised violence, Kibutsuji Muzan walked forth under the pale moonlight to claim his destiny.

His rightful destiny as a truly Perfect being.

Upon the slopes of Mount Kongou lied Senpou Temple. Once, it was a hermitage dedicated to walking the virtuous path of devotion through strong fists and strict discipline. Once. Now, its occupants strayed from Buddha and fell to depravity. Seduced by the prospect of immortality, they abandoned the path to nirvana in favor of degeneracy beyond what the common man could imagine. Perhaps they convinced themselves that immortality was another path to breaking away from the never-ending cycle of rebirth.

Perhaps in a sense, they were right in immortality being an end to that cycle. One could not continue through a cycle if they did not die in the first place, right?

It did nothing to absolve them of the sins they committed to achieve the Undying state.

A shinobi sat cross-legged within its innermost sanctum, near the chamber that housed the last survivor of the Divine Children of Rejuvenation, Senpou's deviant project and magnum opus. He was no ordinary shinobi – though it was a given that no shinobis were ordinary, to begin with. Among others, however, he was given the special – even exalted – task of safeguarding the Divine Heir of the Dragon.

He was only known as Wolf. It was the only name he was known by. Sekiro was his other name but it had been given to him to Ashina Isshin, who was a grandfather to everyone who served him or caught his interest.

And he… Wolf had chosen his own code to follow. And that code dictated that his liege would be protected at all cost. That was why he grew suspicious when his own Lord kept some choice words to himself regarding Immortal Severance.

He had confronted the other person who knew of what would come if his Lord's goal was achieved: Emma. The doctor who assisted him and Lord Kuro throughout their journey from beginning to end. She revealed to him the daunting truth. For Immortal Severance to be achieved, the Divine Heir must be "beheaded" after ingesting the Tears of the Dragon with the Mortal Blade.

In other words, Lord Kuro had to die.

Wolf had been horrified by the revelation and agreed with Emma in finding another way without hesitation.

He did not want to kill his lord but he also wanted to honor his wish. Thus, with the gentle doctor's help, he sought out alternatives and found one in the form of notes and journals left behind by Lord Takeru – the previous Divine Heir – and Lady Tomoe, who had unknown relations with the former. The answer lied in the flower of the Everblossom. The tree in question, however, had perished three years prior and was no longer accessible in the present time.

Afterward, Emma had been forlorn and hesitant to reveal something. What that something was, he did not know. Even when he confronted her at the Sculptor's temple, she did not want to tell him until he pressed her for it. So she told him. She told him that in order for the Divine Heir to be purified with the Everblossom, those oathbound must die in their place, for they shackle their master to the mortal realm.

In other words, Wolf must die in his Lord's stead.

He had accepted that fate without question. He would gladly surrender his life if it meant that his liege would live. That was why he entered the memory of his late father, confronted an Owl at his prime underneath the burning Hirata estate, and slain him a second time.

It did not stop Emma from holding hope that he would find another way.

It did not stop others from wishing for him to live.

He had only returned to Senpou's innermost sanctum to say his goodbyes to the Divine Child of Rejuvenation, only to find that she had disappeared. He found her in the Hall of Illusions, speaking to the other Divine Children who had passed. She gave him her own solution to his dilemma. One entirely different from the ones Emma and Lord Kuro had arrived at; a conclusion that was arrived at by a regretful High Priest and passed down in the hopes of atonement.

Instead of severing the ties of immortality, the Dragon's Heritage would be taken home instead. That way, neither Lord Kuro nor he would need to die and the greed and suffering that were inadvertently brought forth by the Divine Dragon would die away with time, just as though immortality was severed. Lord Kuro and he would live, and his Lord's will would still be fulfilled.

Compared with the two other choices, it was clear what Wolf's decision would be.

So now he sat in meditation before a Sculptor's Idol, a ceremonial mask of the Okami warrior women adorned on his head, waiting as the Divine Child of Rejuvenation finished conducting the cradling ritual. The journey ahead would be long, he predicted. Neither he nor his new charge knew where the Divine Dragon's home was, only that it was in the west. That was why he would take this time to commune with the idol to restore himself back to his peak as a master shinobi, or perhaps even further.

Still, there was something in the back of his mind that nagged at him for forgetting something. It was not related to the Dragon by any means, but-

A sudden shift in the wind stirred him from his meditation and alerted him, his previous thoughts quickly cast aside. He jumped from his cross-legged position and turned, the Shinobi Prosthetic immediately gripped onto Kusabimaru, his constant companion since that fateful night, and his eyes focused sharply on the sudden appearance of an uninvited guest.

A man… something, he immediately rectified, loosely clothed in a kimono. Not Interior Ministry. Not remnants of the late Ashina. Not anything he was familiar with or had a fleeting epiphany of. But that thing was undoubtedly a threat.

What did it want?

Violence. Malice. There was no hint of compassion in that falsehood of a countenance. The scent of blood oozed and permeated from the wretch smiling at him, indicating an earlier slaughter committed by its hands. The degenerate Senpou monks' blood? Plausible. A breathing pattern so inhumanly erratic that Wolf immediately deduced that a monster, a Demon, taking the form of a human was standing in front of him. How many lives had been lost by its hands, aside from the population of Senpou? How many were ruined?

Faintly, he recalled the late Isshin recounting a moment – over an adequate number of servings of Monkey Booze, no less – in his early life slaying Shura, or at least something very much like it. Was that what was standing before him now?

Something in his mind uttered in the negative. He ignored it.

Whatever it was, it was not allowed to come any further.

Kusabimaru was drawn and raised firmly. Wolf calmed, his breathing controlled. His body, tempered and energized by the five esoteric texts that he found or was given through his journey, became taut.

All of his focus was etched upon the Demon. Nothing distracted him. Not the sudden emergence of the wind, not the sudden tumult of the water seated about the sanctum, not the faint light emitting behind him within the Divine Child's temple, and especially not the Dancing Dragon Mask on his face.

"Shinobi." The aberrant sneered at his resistance. "If you value your life, you will step aside."

Its voice uttered heresy. The Prosthetic's strings creaked.

"You shall not touch my liege," he whispered as the monster approached.

"You shall not pass."

A/N: As I said, the two are practically made for each other. Is it because there is no proper story that can be written? Well, I'm here to disagree and this is my proof.

This is Part 1 of the prologue arc. Wolf and Muzan fight against each other in the arc that binds the two worlds together. Expect changes to the canon story because of this meeting. Also, expect the prologue arc to be finished by the time anniversary rolls around.

P a treon. com (slash) DarkAkatsuk1