Chapter Text
The boy is not his brother.
It might have been over four hundred years, but Kokushibou would never mistake this child for Yoriichi. He may have long forgotten the faces of his parents, his wife, his children, but not his twin. Never his twin.
His little brother had been a titan amongst men ( monster , Muzan's cells inside him babble in terror), loved by the world and blessed by the gods. His face had been clear and still like a lake, rarely disturbed by emotions, and for all of his strength and skill, Yoriichi had walked the earth like a silent ghost, as though afraid to leave any footprints in the sand. Always trying to make himself smaller than he really was, longing for that peaceful, simple life where he was nothing more than a man, a brother and husband and father. The only times he showed his true might was when he came face to face with a demon.
In all other aspects of life, though, Yoriichi had been soft, gentle, nearly delicate.
There is nothing delicate about this boy; his hands are rough with scars and calluses, the result of a life of hard work making charcoal and providing for his family. His body is short and lean, speaking of one-too-many missed meals, but there’s still a subtle strength in the way he brings down the axe on the wood chunks, how he shoulders the heavy basket and travels up and down the mountain with his burden every other day.
He is not loud, exactly, but certainly excitable enough, not afraid to make himself heard. Willing to join in on the younger children's games when not busy being the man of the house. His face is a study in human emotion, displaying every thought and facet imaginable, the depth of his feelings nearly breath-taking to see. Upper Moon Two could use some pointers.
But apart from a few surface similarities, the child doesn't even really look like Yoriiichi. The eye shape is all wrong for one, and the color is too dark. His face's bone structure is completely different from the refined, aristocratic features passed down their noble bloodline. Even the mark on his face is wrong; instead of that flame-shaped birthmark, there’s only a burn scar marring the left corner of his forehead.
There is nothing of Yoriichi in this boy, nothing but the hanafuda dangling from his ears.
(Nothing but that same empathy, that same unbearable kindness, the disgustingly soft look in his eyes when he looks at him-)
The boy’s name is Kamado. That’s what the villagers at the foot of the mountain call out when he comes to sell his charcoal.
Kamado Tanjirou.
And Kokushibou has to wonder.
As far as he's aware, Yoriichi had no children. His first marriage had been an ill-fated, short-lived affair, the wife dying together with their unborn child. Kokushibou's own descendants might still be running around somewhere, but the Kamados are definitely not them.
It’s possible, he supposes, that Yoriichi could’ve had a child later in life and decided to hide them in this forgotten corner of the world. It would certainly fit his brother.
And it would also explain why, everytime Kokushibou looks at the boy, he sees his twin. In spite of all the differences, the doubts and impossibilities, Kokushibou sees Yoriichi.
He sees Yoriichi in the way the boy does everything in his power to lessen the burden on his mother, the way he consoles his younger siblings when they hurt themselves playing. He sees Yoriichi when the boy takes off his outer layers in the freezing snow so his youngest sister won't go cold, when he sneakily returns half his portion of dinner to the pot so his family will have just that bit more.
Yoriichi, Yoriichi, Yoriichi.
Their meeting, if it could be called that, had been a complete coincidence. His Lord had sent him to scout this mountain, having caught whispers of the appearance of a beautiful flower that only bloomed at its peak. Though the information was potentially valuable, it wasn't the first of its kind, and certainly not promising enough to warrant a visit from the Demon King himself.
So he had sent Kokushibou after it, since, in his words, "not like you've been doing much else these days".
A statement he somewhat resented. He may not have found Ubayashiki's hideout, but neither had anyone else. Regardless, here he is now, doing Akaza's job for him and investigating this newest rumor of the blue spider lily.
Only to then stumble across Kamado Tanjirou.
A scouting mission that should have lasted only a few days at most stretches into nearly a week. Kokushibou lingers around the family's hut, barely being forced to move thanks to the clouds and the trees’ dense foliage providing cover from the sun.
He hides in their shadows, watching Kamado Tanjirou live that peaceful, simple life his little brother dreamed of.
And ever so slowly, a part of Kokushibou, the one that still remembers the name Michikatsu, that holds onto the broken pieces of a crudely carved flute hidden in the folds of his kimono, begins to yearn .
It startles him, the sheer intensity of this need. Kokushibou has not truly desired anything apart from perfecting his swordplay in literal centuries. The fact that here and now he has come into contact with something - someone - capable of invoking such a reaction from him should be a matter of concern. It should make him uneasy, prompt him to turn around and leave this mountain with the intent to never return. Or better yet, make him step forward and simply erase what caused him to feel this.
Kokushibo does neither. He rests his back against the tree behind him and waits for the sun to sink over the horizon. Never once do his eyes (all three pairs of them) move away from the boy.
He’s not the only one watching.
Kokushibou. His master’s voice has not sounded this wrathful since the end of the Sengoku Era. What is the meaning of this?
This, being the ghost of Yoriichi trudging through the knee-high snow while laughing and pulling a cart where three of his giggling siblings sit.
My lord, the Upper Moon greets before pausing when it dawns on him he has nothing else to say. What could he say that would explain or excuse the impossible sight before them? Both him and his master had worked so diligently, after all, to make sure that everyone who knew of the Breath of the Sun died before it could be passed on. To make sure that any vestige of his younger brother was wiped away from the face of the earth.
Clearly, something had been overlooked.
Clearly, comes that venomous voice. But you will be making up for this failure, won’t you Kokushibou? Kill them all.
Especially that boy.
And for the first time in centuries, Kokushibou… hesitates.
The next second he is hunching over in agony, every cell in his body rebelling and screaming at him, blood pouring from his eyes and mouth.
You dare, Muzan spits in fury. After everything I gave you. You would deny me now?
“I-“ the demon coughs, bracing himself against the tree trunk. Breath, Kokushibou orders himself. In and out . He ignores the blood dripping from his face. “My lord, it's just…”
It just… feels like such a waste.
The thought makes Muzan pause in delivering his punishment. The pain recedes just long enough for him to sift through Kokushibou’s jumbled thoughts, pausing at the idea that had been quietly brewing in the back of his mind for days now.
Since the first time he caught sight of Kamado Tanjirou, to be precise.
What a ridiculous idea, his lord scoffs. There is derision there, so much scorn that it would burn a lesser man.
But he doesn’t say anything else. He doesn’t repeat his previous order, doesn’t punish Kokushibo anew for daring to think such a thing. Kokushibou knows his master, has become adept at navigating his moods and whims through the years. So he waits, keeping his mind blank, his breath steady.
In and out. In and out.
Finally, after a small eternity, the King of Demons speaks again.
Test him. Find out if he inherited more from that man than those earrings.
And if he has?
Bring him to me. Let me decide if desecrating that man’s legacy will be worth the hassle.
Muzan’s presence in his head disappears as suddenly as it arrived, and Kokushibou’s mind is his own once again, or as much as it’s been since he accepted his lord’s offer so long ago.
He had been eager then, almost hopeful, certain that good things - better things - awaited him in the near future. On that roof under the moonlight, he had seen the shape of his dreams take form and crystallize, tasting them on the tip of his tongue.
They had tasted like blood.
Before the sun rises again, Kokushibou is certain; he will taste it again tonight.
Tanjirou feels like he’s going mad.
It’s been a week now. A week since he was last able to sleep peacefully, where he didn’t look over his shoulder every time he stepped out of their home. A week of frazzled nerves and jumping at shadows, feeling eyes staring at the back of his head.
A week of smelling blood in the air.
Was there a bear hunting in the mountain? A bear that wasn’t able to hibernate? It wouldn’t be the first time. Or maybe there is someone out there, hurt?
These thoughts refuse to leave his mind, lingering at the edges and taking a front row seat every time his eyes turn to the forest. It doesn’t take long for his family to notice something’s wrong with the eldest son.
Even little Rokuta notices the changes with his big brother. That night after dinner, long after most of the family has gone to sleep, he crawls away from their mother’s side and into Tanjirou’s lap, looking up at him with big red eyes.
“Nii-chan, don’t be sad.”
Tanjirou laughs, shoulders losing some of their tension.
“I’m not sad, Rokuta,” he tells his youngest brother. “Just worried.”
“Worried?” He tilts his head like an adorably confused bunny.
Resisting the urge to coo over him, Tanjirou pats his head instead, thinking over the best way to explain it. “It means I’m a little scared.”
Rokuta sits up straight, chubby face blazing with all the determination of a four years old. “Nii-chan, don't be scared! I will protect nii-chan!”
The laugh that bursts out of Tanjirou is a joyous, warm thing. His arms come up to gather Rokuta in his arms, cuddling the child closer to his chest. “Thank you, Rokuta. I feel much safer now. But do you want to know a secret?”
Wide-eyed, Rokuta nodded. In the most serious tone he can muster, Tanjirou says “It’s the older brother’s duty to look after his younger siblings. So if you’re ever hurt or afraid, just call me, okay? No matter what, Nii-chan will always come for you.”
Just then, a draft blows through the open window and Tanjirou’s spine goes taut.
The smell of blood is nearly overwhelming.
It’s here.
Oh, gods, it’s here.
“Nii-chan?”
Slowly, Tanjirou nudges Rokuta off his lap. In a gentle but firm tone of voice, he tells him “Go back to okaa-san, Rokuta.” Then he reaches out to the person sleeping next to him, shaking Nezuko awake.
“Onii-chan? Wha…” She asks blearily, rubbing at her eyes. There must be something on his face, for the moment she focuses on it her expression loses any sign of sleepiness, becoming stiff with tension instead. Worry bleeds into her next words. “What’s wrong?”
“Wake up okaa-san and the others,” he whispers, lifting a finger to his mouth. “And be very, very quiet.”
His eyes turn toward the door to their home.
“There is something outside.”
There’s a monster-
As Nezuko hurries to obey him, Tanjirou moves as quickly and silently as he can towards their kitchen, in search of their biggest knife. For a moment, he curses himself for leaving the axe outside. Never again, he promises, resolutely ignoring the thought that there might not be a next time.
By the time he stands in front of the door, fingers closed around the knife's handle, his whole family is awake and watching him anxiously.
Tanjirou points towards the back door, signaling the escape route to be used if things get dire, trying to send them a reassuring smile. Before he can even open his mouth though, there’s a knock on the door.
Absurdly, the first thing to cross his head is how unexpectedly polite.
Then fear floods him, because he had been prepared to fight off a wild animal. Had hoped that the thing prowling outside was a hungry bear. His father had taught Tanjirou how to handle such beasts.
He doesn’t know how to handle the type of monster that knocks on their door wearing a human face.
It gets worse though; it speaks.
“I know… you are awake,” it says. The voice is male, calm, even, sounding almost apathetic. The words fill the air slowly, as if he is pondering and deliberating over every syllable. No matter how hard he tries, Tanjirou can’t find a single trace of violence or bloodthirst hidden in them. By all accounts, it should be reassuring, but it only makes the terror in his gut deepen.
“Come out.”
Tanjirou’s grip tightens around the knife’s handle.
“Come out… or I will come in.”
His mother makes to move towards him, hand outstretched to hold him back. “Tanjirou-“
He moves faster. In the space of a few heartbeats, Tanjirou is out of the house, firmly closing the door behind him, before his mother can even finish her sentence.
The moment Tanjirou lifts his head to see what kind of yokai has come to haunt his family, he realizes two things.
The first, he was right; it really is a monster. He’s so glad he didn’t give it an excuse to barge inside his home.
The second: Tanjirou is going to die tonight.
There’s no question about it; it’s an unchangeable, immovable truth. If he runs, he dies. If he fights, he dies. There’s no chance of survival, only the hope that he can last long enough to give his family time to escape.
That calms his nerves. His hands, that he hadn’t even noticed were shaking, gradually stop. Tanjirou bends his knees a little, preparing to move at any second, keeping the knife held out in front of his body defensively. He has a goal to work towards now.
He must protect his family. As the eldest son, the oldest brother, he cannot allow them to come to harm. That was the duty his father passed down to him along with his earrings. Tanjirou is about to go meet him in heaven. He will do so with his head held high, secure in the knowledge he did his duty.
The monster tilts his head, looking mildly intrigued.
“Interesting… your fear… has nearly disappeared completely. I wonder… why?”
The being that speaks these words could have stepped out of his worst nightmares, Tanjirou thinks. A tall and strong man, with a sword hanging from his waist, he could almost be confused with those samurai of old, who roamed the land in service of their liege lord.
The illusion shatters as soon as you get a glimpse of his face.
Flame-like marks crawl across the left side of his face and his right chin, but those are nothing compared to the rest. Eyes, six of them, take up residence on the creature's face, from high on his forehead down to his cheeks. They are a vivid, sickening yellow, glowing in the darkness, surrounded by blood-red sclera. The middle pair bears kanji characters instead of pupils; 上弦 and 壱.
Upper Moon One.
What are you, Tanjirou almost blurts out the question, only to swallow it back. It’s obvious in hindsight. Hasn’t he grown up listening to his grandma’s and father’s tales about the monsters who came out at night, hungry for human flesh?
But those were stories. Just scary tales to keep children in their beds.
They weren’t supposed to be real.
“What do you want?”
Tanjirou is proud of the way his voice doesn’t shake.
“I am curious. Does the name… Tsugikuni Yoriichi… mean anything to you?”
The question stumps him. Out of everything Tanjirou expects, being asked if he knows some stranger isn’t anywhere near his list.
The demon reads the confusion in his face. “I see… Unsurprising. It's been… so many years.”
Tanjirou tenses in preparation when the demon’s hand falls on the hilt of his sword.
“Boy,” he calls. “If you want to live…
Fight me.”
***
Not for the first time, Tomioka Giyuu curses himself.
They had received reports of a strong demon being sighted around the area over the past week, so powerful in fact there were suspicions of it being one of the Twelve Kizuki. So naturally a Hashira was sent to investigate.
Either the demon is one of Muzan’ Kizuki, Giyuu doesn’t know. What he does know is that it can cover its tracks exceptionally well. There are no trails of bodies and destruction to follow, no destroyed families or wailing survivors. And while this is, of course, a good thing, it makes Giyuu feel more nervous that when he does find the demon, something awful will happen.
He’s right.
He’s been wandering the mountain for most of the night when his ears pick up the sound of fighting. The clash of steel on steel, the screams of children.
He bursts inside the clearing, nichirin blade at the ready, only to pause in shock at the sight before him.
That’s an Upper Moon.
Not just any Upper Moon, but Upper Moon One, judging by the kanji carved into his eyes. The strongest demon in existence, second only to Kibutsuji Muzan himself.
And he is… smiling.
“Good, good,” he praises the screaming man- no, the boy, that’s a child - while sidestepping a knife stab, only to have to dodge again to avoid being nicked by a swinging axe. “You have potential. Untrained, untapped… but it’s there.”
Behind the knife and axe-wielding boy, he can see another one, even younger, laid out on the snow and missing an arm. There are more bodies spread out on the ground ( too slow, too slow, you’re always too slow- ), and Giyuu can’t tell if they are alive or not. He forces himself not to look at them closely enough to find out. He can’t afford anymore distractions. Right now, there’s for sure one person still alive.
No matter what, Giyuu will save that boy.
Breath of the Water, First Form: Water Surface Slash.
“This doesn’t concern you, slayer. Stay out of it.”
He doesn’t blink. His eyes never once leave his target. So he really has no excuse not to see the demon move but the obvious: Upper Moon One is just that fast.
One moment he is rushing towards the demon, blade poised to take off his head; the next, his back meets a tree, the impact enough to crack the bark beneath him and punch all breath from his body. He can feel no less than three broken ribs, one of which might be digging dangerously close to his lungs. Added to that, there are deep slashes gouged on his side from the demon’s claw, which spill an alarming amount of blood.
He has lost his grip on his sword ( how pathetic can you get ) and watches as it goes flying in the direction of-
The boy. The red-haired, desperate boy.
He doesn’t hesitate. He lets go of the kitchen knife, catching the sword mid-air, barely pausing in his momentum as he hurls himself at the demon who slaughtered his family, screaming in rage.
If he had any breath left, Giyuu would have shouted at him to run.
But then the boy does the impossible; the untrained, clearly civilian child, instead of waving and slashing the sword around like Giyuu half-expects to happen, moves into an unfamiliar stance and performs what is clearly a Breath Technique.
For a moment, Giyuu swears he sees the specter of flames. It’s enough to shock him.
Upper Moon One clearly shares the feeling, because the move actually catches him; or, rather, it would be better to say that it manages to graze the sleeve of his kimono.
Even the boy looks surprised at this success.
It doesn’t last long.
The next second, the boy is on his hands and knees, sword forgotten on the snow as he coughs and gasps, lungs desperately trying to gather air.
Of course, a distant part of Giyuu’s mind notes. He hasn’t been trained in the proper breath techniques, his body can’t withstand the sudden pressure.
He won’t be able to walk for the next hour, at least, much less run.
That boy is dead. I failed him.
(Again)
Giyuu tries once again to rise, only to fall back against the tree, blood gushing anew from the wound on his stomach. Total Concentration Constant might have slowed the bleeding down some, but if he doesn’t get treatment soon, Giyuu has no illusions about the odds of his survival.
Meaning, they’re quickly reaching zero and heading towards the negatives.
“I knew it. You are… his child,” Upper Moon One announces. “My lord… did you see?”
‘My lord’? … wait, does he mean-
The demon inclines his head as though listening to a voice on the wind. Then he sheaths his sword and picks up the boy by the throat, lifting him until they are at eye(s) level.
Giyuu once again tries to rise, bracing himself against the tree and cursing his weakness with more vitriol than usual.
“Rejoice… Kamado Tanjirou. You’ve been chosen… to stand among the greatest.”
Kamado Tanjirou gurgles, nails digging into the hand holding him up, trying to claw it away.
“Nakime, take us back.”
The sound of a biwa cuts through the night as shoji doors appear out of thin air, clearly the result of a Blood Demon Art.
And Giyuu knows that if he lets Upper Moon One drag Kamado through these doors, something worse than death will be awaiting that boy.
Ignoring his body’s warnings to stay still, he lurches forward, prepared to do whatever is necessary to stop what’s about to happen.
But Giyuu-
Giyuu has always been too slow, especially when it counted the most.
For a split second, he meets the boy’s - Kamado Tanjirou’s - eyes.
Their hands reach out for each other.
Please. Help me.
The tip of their fingers brush.
Ah. What kind, sad eyes.
The shoji doors slam shut between them.
His family is-
He failed.
Tanjirou… couldn’t keep them safe.
They are all-
“What are you doing?! Get back! Takeo, get back!”
“I won’t leave you!”
Takeo rushing at the demon, axe in hand, only to lose his whole arm and be sent flying.
“Takeo! Onii-chan!”
“Nekuzo, don’t-!”
A flash of claws and his sister is face-down on the ground, hot blood seeping into the snow around her.
“Don’t you touch my children!”
A choked “Mom-!”
Again.
“Okaa-san! Onii-chan, onee-chan! She’s hurt, kaa-chan is hurt-!”
Hanako.
“Stay away from us! Go away! Leave us alone!”
Shigeru.
“ONII-CHAN!”
Oh, god, Rokuta.
They are all- they-
“Is it done?”
“Yes, my lord.”
“What about the slayer?”
“He might survive… if he receives medical attention. Considering how remote the location… it's unlikely.”
“Hmm. Let me see it then. Show me your prize, Kokushibou.”
A clawed hand grips his hair and forces his head up, up, up, until he’s staring at a man- no, a demon, another one, with plum-red eyes, slit like a cat’s.
The demon looks down at him like he’s the scum of the earth, worse than trash. One of his hands comes to grip his jaw, sharp nails cruelly digging into his flesh and drawing blood.
Tanjirou barely blinks.
His family is-
“How disgusting. You really do look like him.”
A moment of silence passes.
“You clearly know the Divine Breath too, even if you’re incapable of using it to its full potential. Certainly nothing like that man. I wonder… it would be wonderful, wouldn’t it, to see that Breath corrupted by a demon’s Blood Art? Wouldn’t it be nice, having the complete set? Sun and Moon, both kneeling at my feet…”
A considering, more thoughtful pause.
“… It would feel like poetic justice, wouldn’t it? Right here and now, I can end that man’s legacy in the worst possible way imaginable. He must be rolling in his grave, knowing what’s about to happen to you…”
The hand gripping his face tightens, and somewhere in the midst of his grief, Tanjirou realizes that something very bad is about to happen to him.
His brain has difficulty believing it. What more could happen? What’s worse than his family-
His family-
The demon leans down until his mouth brushes the shell of Tanjirou’s ear. “I look forward to seeing what kind of demon you become, Kamado Tanjirou.”
There’s a hand on his chest. In his chest, piercing his heart -
“You will serve me well.”
And then there’s nothing but fire .
***
“He will be your responsibility from now on. Be sure to keep him in line, Kokushibou.”
“Of course, my lord.”
***
When Tanjirou opens his eyes, he is greeted by such a beautiful sight he nearly collapses to his knees.
That’s dad. And mom. And his siblings.
They are there. They are right there.
“You guys are all-!”
Dead.
He stops. Looks around.
There’s a river between him and his family.
He stands on a desolate, sandy riverbank, everything behind him swallowed by darkness.
On the other side of the river, the world flourishes into verdant pastures and blue skies. His family is there, laughing and smiling without a care. Tanjirou can see his father, healthier than he remembers, wrap his arms around his mother’s shoulder. His mother, who smiles brightly, joyful in a way she was never able to quite be again since the death of her husband. There is Nezuko teaching Hanako to make flower crowns and Takeo chasing Shigeru around in circles, the two shrieking with laughter.
They look so happy.
He wants to go. He wants to join them. He takes a step forward-
“You can’t go there yet.”
Tanjirou freezes. That voice. That voice, he knows that voice, it-
No. No, this one is… softer. Kinder.
Sadder.
When he turns around, there’s a red-haired man staring back at him. His face is twisted in a heartbreaking expression as he looks at Tanjirou.
“I’m so sorry, child.”
The man is crying. For me?
“It’s my fault. You and your family had to pay the price of my own weakness.”
“I don’t understand. W-who are you? What’s happening to me?”
He can feel it now, if he concentrates. That liquid fire running through his veins, burning him alive. Distantly, he hears someone screaming. It takes him a moment to realize it’s himself.
What’s happening to me?
“Your body is changing. When you wake, you will be a demon.”
A demon.
Six eyes staring hungrily at him, Upper Moon One branded over them. Another pair of eyes, plum-colored and slitted but equally hungry, equally monstrous, with a serpent’s voice whispering poison in his ears.
You will serve me well.
“No,” a choked sob escapes his mouth. “No, no, please, I can’t- let me go- I have to go- my family, they are there, they are right there -“
“But Tanjirou. Where’s Rokuta?”
“ONII-CHAN!”
It’s like the ground disappears beneath him. Tanjirou falls to his knees on the gray sand, staring first at this man and then at his family on the other side. Numbly, even though he already knows what he will find, he begins a headcount. There’s his father, his mother, Nezuko, Takeo, Hanako, Shigeru…
Where is Rokuta?
A hand falls on his trembling shoulders. “You cannot go there yet, Tanjirou. Your brother is still waiting for you to come back.”
“Nii-chan will always be here, to love and keep you safe.”
That’s what he said to Rokuta. No matter what, Tanjirou would always be there for him.
But I failed. I left him alone. Left him behind.
If I cross this river, who’s going to take care of him?
“What do I do?” Tanjirou whispers. “Mister, what do I do?”
He sounds like a child. Feels much like one too, too small and afraid to face the world. He wants his dad, Tanjirou realizes. He wants Tanjurou’s arms around his shoulders, wants to smell that familiar fragrance of burning pine and medicinal herbs.
It’s not his father’s arms that pull him into a hug, but the feeling of safety that engulfs him is the same.
“You must be strong,” the stranger tells him, holding him tight even as Tanjirou nearly rips his kimono with the force of his desperate grip. “The path ahead of you will be filled with hardships. You won’t remember this, your human life, for a long time. And they will try to keep it that way, to keep you ignorant, submissive. They will try to tempt you, Tanjirou. You must not give in, no matter how hungry you get. If you do, then it’s over. Kamado Tanjirou will die. Your little brother will die. You must not eat .”
Tanjirou sobs. The fire in his veins is getting closer, hotter. He can feel it rushing at him now, a kind of agony that he couldn’t have imagined in his worst nightmares. Consuming him. Changing him.
“You still have a duty to fulfill. Find Rokuta. Get your memories back. Only then will you be able to fight against these chains. Once you do… you need only dance.”
“Wha-“
A scream cuts off his next question. He loses control of his body, not falling to the ground only by virtue of the hands still holding on to him. Even as Tanjirou shrieks and struggles, the man doesn’t let go of him.
The world around him is getting darker. He can’t see his family on the other side of the river anymore, and that hurts worse than the magma bubbling inside him.
“Listen to me, Tanjirou,” the man grabs his head, forcing him to look into his eyes. They are kind. And so, so sad. A part of Tanjirou wants to soothe away the sorrow in those dark eyes. And he still doesn’t know the man’s name. He hadn’t asked. How rude of him, his mother would give him an earful later…
“When it gets to be too much, go to sleep.”
Dreams? Yes, that sounds lovely. He really wants to go to sleep now. To have good dreams, somewhere where that doesn’t hurt and his family is safe and happy…
“Your family loves you. You can forget everything else, but never that. You are loved, Kamado Tanjirou.”
He feels so warm…
“Now wake up.”
***
When are you going to wake up?
It’s been over a day.
Twenty nine hours since he slaughtered the boy’s family. Since he brought him to the Infinity Fortress and deposited him in front of his master.
Twenty nine hours since Muzan gave his blood to the child, who, after spending a small eternity writhing and screaming his throat raw, had fallen silent and still.
Had the boy been a demon slayer, trained in breathing techniques, it would explain the delay in the transformation, but Kokushibou had tested him himself. The boy was capable of some bastardized form of Sun Breathing, but he clearly hadn’t received a swordsman’s training. There were no signs of such.
So then, could it be that the boy’s will is just that strong? It had happened before, people who abhorred the prospect of being demons so much that they would perish before the transition could be completed, even though their bodies had already acclimatized to Muzan’s cells.
If it is so… then that means that Kokushibou has spent the last day sequestered away in one of Nakime’s rooms for absolutely nothing, babysitting a corpse.
It means that he will never get the chance to see how much stronger the child could grow with the proper guidance and training. That he will never see the boy’s eyes - those familiar, expressive red eyes - open again.
What a waste.
And Kokushibou had been so looking forward to it, too. He won’t deny there had been a certain… anticipation, a guilty pleasure of sorts, at the thought of seeing someone so alike that little brother of his, brought down, brought low enough as to become a demon, to serve the man Yoriichi had dedicated his life to kill. When the idea had first crossed his mind back in that mountain, Kokushibou had been so overcome he had lost control of his breathing.
It felt almost… sacrilegious, to think of tainting his brother’s legacy like that. But what a beautiful, tempting daydream it made; to see Yoriichi’s descendant, if not the man himself, becoming the thing he was sworn to hunt and destroy. To see him reduced to something so utterly inhumane, crouched over a body, mouth and hands red with blood…
Are you watching, Yoriichi? Do you weep for this lost child of yours?
Abruptly, Kokushibou remembers the first and last time he had seen tears track down Yoriichi’s face.
“ Brother, this is heart-wrenching.”
Something rips, and when Kokushibou looks down he sees his claws have shredded through the tatami mat.
Ah, he feels sick again. Even dead and gone, Yoriichi always manages to drag the worst out of him.
“But not this time,” he says to the room at large, as though his little brother is present and able to hear him. “There’s nothing you can do now, Yoriichi.”
I win this time, Yoriichi.
Even if, after everything, the boy dies; even if Kokushibou has to get rid of the rotting corpse by the end of the day - he will have won. The last remnant of his cursed, beloved brother will die together with the child, until the only place Yoriichi lives at all is in Kokushibou’s own memories-
A whimper breaks him away from his thoughts. Slowly, with a deep sense of excitement stirring inside him, Kokushibou looks down.
Bright, blood-red irises greet him through a sleepy daze, shot through by golden filaments originating from the slitted pupil. Like a sunburst , Kokushibou thinks. How appropriate.
That’s far from the only difference; the injuries from their altercation (it can’t really be called a fight) have long since healed, as did the hole in the boy’s chest from where Muzan had injected his blood, but that’s to be expected. Kokushibou can see, through the Transparent World, the way his master’s cells run through the new demon’s body, giving the final touches here and there. Strengthening bone and sinew, facilitating healing and stopping aging, making this boy more powerful than he could ever hope to be as a man in his prime.
But the inner happenings of the boy’s body are not as interesting as what’s happening outside. Before Kokushibou’s very eyes, slayer marks - can they even be called slayer marks like this? - creep like vines all over his skin. The burn scar the child sported on the upper left side of his face changes; darkening and twisting like a living flame, eating its way downwards, over his eye and across the bridge of his nose. More marks appear in his forehead, forming a crown of flames. They grow and spread, running down his cheeks to his jaw and disappearing beneath the collar of his haori.
There’s an odd sort of delight as Kokushibou studies these marks, their meaning clear as day. Pride and exhilaration well up inside him as he watches the former human blink his eyes open to a new life.
His brother’s living, breathing legacy: a demon.
I won , Yoriichi.
“M-mister? Who are you? Where are we?”
Kokushibou raises an eyebrow, studying the new demon. His voice comes out dry and parched, and though he seems confused, there is none of the mindless hunger he expects. Already, the child is proving himself different. Unique.
Resentment stabs at him. Yoriichi was always special too.
“What do you remember?” he asks shortly as he watches the boy get to his knees.
The silence that follows is damning.
“…I don’t… I can’t remember, I-I think…” the boy stutters to a stop. “… I don’t remember anything.”
Kokushibou looks at the fidgeting child, letting the silence grow. While some memory loss is the norm, total amnesia is uncommon. Among the Upper Moons, only Daki and Akaza have absolutely no memory of their human past, though he has long suspected the martial artist is more affected by it than most.
Nonetheless, this leaves Kokushibou in a conundrum. Should he reveal what little he knows about Kamado’s past? Who would that benefit? Certainly not the young demon in front of him, looking lost and afraid as he stares up at the Upper Moon as though he holds all the answers in the world.
The look feels strangely familiar. Did his own children look at him like that, once upon a time? He can’t remember.
( Yoriichi did. Yoriichi looked at him like Michikatsu was his whole world, like there was no bigger or brighter star in the sky -)
“We are… in the Infinity Castle,” Kokushibou finally says once it looks like the boy will actually start crying. For some reason, he doesn't want to see these tears. “Our lord… allowed us to stay here… as you recuperate from the transformation.”
“Transformation?”
Doesn’t he even know what he is now?
“Our lord…. has given you… a gift. He has made you into a demon… granting you power and eternal life. Be grateful,” he tells the child sternly.
The boy nods automatically before pausing and looking up at him almost… hopefully?
“And do you or your- our lord,” he corrects himself at Kokushibou’s glare. “Does he know who…. who I am?”
Kokushibou weighs the pros and cons of telling him, before ultimately deciding against it. The human Kamado Tanjirou is dead and gone. He will not be coming back.
Like Kokushibou himself, this boy has been reborn under the moonlight. The demon before him deserves a new name, to go with his new life.
"Your name is Hikage."
The newly-named Hikage mouths the word to himself. The confusion has not left his face, if anything it has only grown, his subconscious mind understanding this name is unfamiliar, but that’s easily overshadowed by the relief at finally having something of his own when he has lost everything else.
Then Hikage turns back to him, demonic eyes almost innocent in their curiosity.
"And who are you, sir?"
For a long time, Kokushibou says nothing. And then-
"Others… call me Kokushibo... but you will call me Aniue."