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Sins of the Moon

Summary:

Muichirō Tokitō lives by mission alone, his world reduced to fading memories and scribbled notes. But when a routine investigation into a shape-shifting demon leads him to a town plaza at midnight, the Mist Hashira is confronted with a face he doesn’t recognise, but his blood does. Taking the form of a majestic swordsman, the demon awakens a chilling mix of fear and reverence. Ready or not, the Mist Hashira is about to confront the progenitor of his bloodline.

And come face-to-face with his past.

Notes:

To anyone who has read, or is currently reading Slayer of the Moon, please don’t be confused. That story was created as a gift for my friend VB, who co-wrote Chapters 1 through 7 with me and continues to contribute ideas while helping oversee the story as a whole.

Over time, though, I’ve grown deeply attached to the premise and found myself envisioning it differently. While the core idea for Slayer of the Moon originated with me, some of its events were shaped by VB’s input.

With their permission, I’ve decided to write my own version of the story. To be completely honest, I want this take to lean fully into a Muichirō-centric perspective. Where Slayer of the Moon explored multiple characters’ arcs and motivations, this version will narrow its focus and centre much more firmly on him.

There will be many differences. For example, Obanai won't be sharing the spotlight with Muichirō here. In fact, I don't think he will be appearing that much.

I won’t be using the same narrative style of a chronological, present-tense timeline interwoven with scattered past-tense memories. That approach belongs to Slayer of the Moon, and I’d rather not repeat it here.

This story also won’t take place in the Swordsmith Village; it isn’t as restricted in setting as the original.

You don’t need to read Slayer of the Moon to understand this fic. They're very different stories anyway.

This story stands entirely on its own.

Chapter 1: Plaza

Summary:

A demon reminds Muichirō of a fragment of his past.

Chapter Text

 

"Do you honestly think that colour matches Muichirō-dono’s skin tone? Stupid! Idiot!"

Muichirō hadn’t been listening to the conversation, but those sharp words caught his attention for a fleeting second.

Who is she berating this time? Muichirō lifted his gaze to see Ginko, his Kasugai Crow, cawing at a flustered Kakushi. The man was frantically trying to select an outfit for Muichirō. Because today, apparently, he wouldn't be wearing his usual Demon Slayer uniform.

Who told me that? he wondered. Ah, probably Ginko. That would make sense.

He sighed and pulled a small notebook from his sleeve. To anyone else, the scribbled notes inside would seem nonsensical, but for Muichirō, they were vital triggers for his drifting memory. It was a practical method; if someone were to snatch it, they wouldn't be able to make sense of his current mission anyway. To be safe, he burnt the pages as soon as a task was complete.

According to his notes, he had to board a train. That was what the drawing of a locomotive meant, right? Why else would he have drawn it? It wasn't as if he had any particular interest in trains.

"His nagagi should be made from the finest silk, do you hear me? This is Muichirō-dono we’re talking about!" Ginko shrieked. "And the haori! How many times must I tell you? Cloud patterns! Idiot! What in the world is that hakama?!"

Ginko was a crow, but she had massive lungs for such a small bird.

I honestly don’t care... Muichirō thought. But since he didn't care enough to say it, he remained silent.

He looked down and wiggled his socked toes. "Maybe I’ll wear zōri instead of geta," he murmured, but it was enough to stop Ginko’s rant mid-sentence.

"Of course! Whatever you wish, Muichirō-dono!" she chirped. Then she turned back to the attendants, her voice returning to a deafening roar. "You heard him! Get the best zōri you have! Move!"

The three Kakushi scrambled in a panic, searching for footwear that would satisfy the crow’s demanding tastes.

Why was I upset this morning?

Muichirō's mind drifted, turning over the question without any particular urgency.

Sword. A kid. A box.

Oh.

A swordsman with a box strapped to his back had confronted him, interrupting Muichirō's training with a long, pointless speech. Still, Muichirō had gotten what he came for; he had shattered the mechanical battle doll’s armour and claimed one of its sword-wielding arms for himself.

Truthfully, he hadn't needed to go that far. Training with the doll would have been enough. But that face... He'd wanted to destroy it so much that he hadn't cared about consequences or who might end up hating him for it. The annoying kid with the hyottoko mask certainly hated him now. 

But it had made Muichirō feel lighter, even if only for a little while, and that was enough.

None of it mattered anymore. He had been there for a reason... though he couldn't quite recall it. If he was no longer there, if no one was pestering him, and if it wasn't written in his notebook, it meant the mission was complete. That was all that mattered.

 

🎴


Two strange things had happened that day. 

The first was the sight of a tall, six-armed figure with its back turned to Tanjirō. Upon closer inspection, however, he realised with a start that it was just a doll. Still, it was unsettling.

The second thing was something he found impossible to accept: a Hashira slapping a child.

Tanjirō knew of the Hashira, at least by their names, and understood they could be stern. However, he hadn’t expected such blatant harshness from a member of the Corps. Compelled by a desire to protect the boy, who wore the traditional hyottoko mask of the Swordsmith Village, Tanjirō rushed in, shouting for the Hashira to release him.

The rescue attempt had failed miserably. Even as Tanjirō clamped his hands around the Hashira’s wrist, the Hashira remained unmoved, holding the child by the collar.

That, Tanjirō decided, was the third strange thing. As he recalled, this Hashira, Tokitō Muichirō, was smaller and thinner than Tanjirō. His pale, round face remained an expressionless mask, and his hazy blue eyes were vacant.

It had been an embarrassing encounter, and Tanjirō found himself hesitant to recount the details to Nezuko. She tilted her head, as if trying to understand how her older brother had been so easily overpowered by someone younger and smaller.

"The thing is, he shouldn't have done it," Tanjirō muttered, unsure if he was trying to convince Nezuko or himself. "And yes, I interrupted his training, and yes, I gave a long speech…according to him. But it still wasn't right."

Tokitō hadn't been wrong; swordsmiths don't fight and cannot kill demons. But as Tanjirō saw it, no swordsman could fight without the Nichirin blades these smiths provided.

Tokitō hadn't bothered to listen to any of that before knocking Tanjirō out. Come to think of it, that wasn't the first time Tokitō had disciplined him physically. During the trial to decide Nezuko’s fate, Tokitō had flicked pebbles at him. Those flicks had hurt more than most people's fists.

Was the Mist Hashira truly that much stronger, or did he simply know where to concentrate his strength? Despite the friction between them, Tanjirō found himself wanting to learn from him.

 

🌫️


 

The locomotive was every bit as massive as Muichirō had expected. Its glossy black body stretched so far that even if he craned his neck, he couldn't see where it began or ended. The passenger cars, however, were still built of wood. It seemed Nippon hadn’t quite caught up with Western technology yet, despite what people claimed.

Speaking of the West: two men in Western-style uniforms were blocking the entrance to their assigned car. One was tall and bearded with sharp, angular features. He explained that there had been a string of thefts on the line, and as a result, every passenger had to be searched.

How exactly that was meant to help, Muichirō couldn't work it out, partly because the man's accent made him difficult to follow. It was obvious he hadn't grown up here. Why a Western man was working in Nippon was a question Muichirō had no interest in pursuing.

The other man, shorter and clearly Nihonjin, repeated the requirement in a Kamigata accent. Or was it called the Kansai accent now? Muichirō must have read something outdated. 

Searched thoroughly. Did that mean they'd be expected to undress in the open, in front of everyone? How absurd.

"Who do you think you are?" Muichirō said.

Out of the corner of his eye, he saw the three Kakushi accompanying him exhale in collective relief. Clearly, they weren't trained to handle this kind of confrontation.

"What gives you the authority to order me to strip in front of strangers? My haori is worth more than your entire existence." 

Ginko, perched on his shoulder, let out a sharp harrumph of agreement.

"It’s just protocol," the shorter man said. He had a soft chin and round cheeks that were flushing with embarrassment, unlike his tall companion, who continued to look down his nose at Muichirō. To be fair, Muichirō was small, and the Westerner was tall even by foreign standards. But the man stared as if he were looking at a bug. "Besides, you won't have to strip. We just need to frisk you.”

"Absolutely not!" Ginko cut in. "Don't you dare lay your filthy hands on my Master, you pig!"

"Pig?!" The Nihonjin flinched. "Sir — Ma'am — please, would you control your pet?"

She’s not a pet, Muichirō thought. He opened his mouth to speak, but Ginko beat him to it.

"Pet?! How dare you! I am a respected member of—"

Muichirō reached up and clamped his hand over the crow’s beak before she could divulge anything classified.

"What she is trying to say," Muichirō said, looking at the tall man, "is that we will cooperate, provided you do not use your hands. One of the attendants I am travelling with is a woman. Is respecting a woman’s boundaries not a concept where you come from?"

The tall man stiffened and scoffed. "Where I am from, democracy is the norm. Men and women are equal. The working class and the aristocrats are the same." His moustache twitched. He took Muichirō for a pampered young lord based on the quality of his silk clothes.

"Everyone is equal where you're from?" Muichirō said, his tone unchanged. "Then tell me… could a cleaner, someone from the working class, simply walk into a high-end restaurant, order whatever they liked, or actually be let through the door?"

"That's not what I—"

"No? Then how can you claim that everyone in your country is treated equally? Either equality exists without conditions, or it doesn't exist at all."

The bearded man opened his mouth to retort, but the Nihonjin cut him off. "Someone dressed like you, accompanied by such well-clothed attendants, surely cannot be a thief. You may go... Ma'am. Sir." He stepped aside, and Muichirō walked past without a word.

He could hear the bearded-moustached man grumbling behind him. But he was on board now, so why would he turn around and keep exchanging words with someone that ignorant?

As it turned out, Mister Moustache was not their only problem.

As Muichirō and the three Kakushi entered the car, they were greeted by passengers who avoided their gaze. He noticed a woman dressed in a high skirt tied just below her bust and a brown jacket with long sleeves.

"Another gaijin," Ginko murmured close to his ear. "I recognise that dress. She's from Chōsen."

The woman's clothing was interesting, more so than the bald infant in her arms, who looked both angry and miserable at the same time.

Two rows behind her sat another pair of gaijin. These two were shorter than Mister Moustache, which meant Muichirō wouldn't have to strain his neck quite as much.

Still, when they stood, they were taller than he. Of course they were.

Just like the men on the platform, they wore railway uniforms.

"Tickets, please," said the one with a flat, drooping face. He looked like a blobfish. Muichirō couldn't fathom why the man was smirking at him.

"Here," said the first Kakushi, pulling four tickets from his breast pocket. Muichirō thought of him as Man One, since he couldn’t be bothered to remember all three names. "And here is the permit for the crow." He produced a document explaining Ginko’s status as a service animal.

Blobfish punched a hole through each ticket, then his smirk stretched wider as he read the permit. "This is quite funny."

"What’s so funny about it?" Ginko demanded, her wings tucked at her sides like arms akimbo.

Blobfish startled. "Y-you can talk?"

"I'm a crow. Of course, I can talk."

"But you talk like a person... You know what? Never mind. I can see why you’re needed, since your owner is mute."

Muichirō tilted his head. "Do I have to?"

Blobfish and his companion laughed. The second guard, a lanky man so thin that Muichirō wondered how he remained upright, stepped forward.

"Your friend there," Stick-man asked, looking past Muichirō’s shoulder at the third Kakushi. "What’s her name?”

Muichirō glanced back at Lady. She was the only female Kakushi in the group, and despite being covered, her build made her gender obvious.

"I don’t know," Muichirō answered. "You’ve punched our tickets and read the permit. Would you mind letting us pass so we can sit down?"

Stick-man’s eyelid twitched. "I was just being polite. It’s polite to ask a lady's name, isn't it?"

Muichirō wasn't sure if that was true, but he was sure that Lady was trying to disappear behind Man Two.

"I’m not sure she feels comfortable," Muichirō said. "So, let us through."

Blobfish unslung a rifle from his back and levelled the muzzle at Muichirō's face. "You run your mouth as if you can do whatever you want," he sneered. "Shame. You're pretty enough, but your voice is too deep for that face. Is that natural, or are you putting it on because you think you're better than us?"

Muichirō felt a dull ache behind his eyes. The logic was missing. Why were these railway workers asking such useless questions?

Sighing, Muichirō stepped forward until his forehead pressed against the cold metal of the muzzle. He felt Ginko stiffen on his shoulder, though she held her ground. Behind him, Lady and Man One began to plead for him to stop.

"Go ahead," Muichirō said. "Shoot."

Blobfish’s eyes widened before he let out a jagged laugh. "Now I don’t care if you’re a man or a woman. I’m going to have fun with—"

Muichirō’s hand shot up. He wrenched the rifle from the guard’s grip and spun it around, pressing the muzzle into the man's own chin.

"I wonder what it would feel like if I actually did it," Muichirō mused, his thumb clicking the hammer back. "It doesn’t take much effort, does it? Even a coward can shoot from this range.”

Muichirō pressed his finger to the trigger, regarding Blobfish through the front sight. In his periphery, he caught Stick-man reaching for his own rifle.

"Go ahead," Muichirō said, without moving the muzzle an inch. "By the time I'm done with him, I can shoot you just as easily."

Stick-man's hand stilled.

The sound of whimpering pulled Muichirō’s focus back to the present. He looked around and realised the entire car was watching them in terrified silence.

Not good. I let my patience snap.

"Master, please... don’t do it," Man One pleaded.

Muichirō had no intention of pulling the trigger. He wasn't going to shoot a civilian; that would be a grave violation of the Demon Slayer Corps' code. However, he relished the expressions on the faces of Blobfish and Stick-man. Some people needed a harsh reminder that carrying a weapon didn't make them untouchable.

"I was just joking," Muichirō said. The corners of his mouth didn't even twitch. "See? Ha. Ha," he added, completely flat.

With a few blurred movements of his fingers, he stripped the rifle of its detachable parts and pocketed the bullets. "Here you go."

Before the second guard could even blink, Muichirō was standing beside him. He snatched Stick-Man’s rifle and dismantled it just as effortlessly as he had the first. He handed the useless pieces back to the stunned men and walked towards his seat.

 

🌫️


By the time they reached their destination, Man One, Man Two, and Lady were still visibly shaken. Though they kept their mouths shut out of respect for his rank, their discomfort was written in their stiff postures.

Except for Lady. As they stepped onto the station platform, she spoke up softly. "Tokitō-dono... thank you for standing up for me. I appreciate it." She kept her gaze fixed on the ground.

Muichirō frowned. Had he done it for her? He tried to reach back into his memory to find his original motivation, but the effort made his head ache. He shrugged and kept walking.

It was late afternoon. The sky was bleeding into a deep, bruised orange, a signal that night would soon conquer the horizon. And with the night came the demons.

Under normal circumstances, the three Kakushi wouldn't accompany a Slayer. Their role was to handle the clean-up after a mission was finished. But Muichirō was a Hashira, and a Hashira capable of killing multiple demons at once could afford to bring them along.

These three had also been the ones to speak with the locals days before his arrival.

As Ginko was now recounting to him, the report described a demon that took on the face and body of whoever the victim either loved most or hated most, whichever would make them hesitate to strike. More often than not, it chose the face of someone already dead. The grief was enough to root a person in place until it was too late.

That said, it hadn't been confirmed as a demon. A human killer was still possible. Until he knew otherwise, Muichirō had to wait and watch.

The sightings were most frequent in the town plaza. As night fell, the markets closed and the streets emptied, leaving the square a ghost town.

"If it really is a demon, I doubt it will show up here tonight," Man Two remarked. "The folks in this town are convinced it's a serial killer. They've all locked themselves indoors."

Muichirō looked at the empty stalls. These people didn't believe in demons. He found himself wishing, briefly, that they were right.

"Or perhaps it will show up here, dragging a new victim, thinking the coast is clear to eat in peace," Muichirō said. "Either way, we have a week to investigate. We wait."

The three Kakushi nodded in sombre agreement as the last of the sun dipped below the rooftops.

Ginko preened Muichirō's hair as the night stretched on. They were well hidden behind the tall buildings, the three Kakushi growing restless beside him.

If they found it boring, they were lucky. Boredom meant they would live another day. As for Muichirō, he would have preferred it to be over already.

As if the world had heard him, he sensed movement before he saw or heard anything.

In the middle of the empty plaza, a man was stumbling backwards, eyes fixed on a dark alley, his entire body trembling. His knees gave out, and he hit the ground, landing hard. "P-please," he said, barely holding together. "I have a family."

They always say that, Muichirō thought, watching without moving. Why did humans bother? Whatever was coming for them clearly didn't care. If it had cared, it wouldn't be coming for them at all.

A low growl rolled through the plaza, and the industrial smell of the area gave way to blood. Beside him, he felt Man One, Man Two, and Lady go rigid. They wanted to run, but fear or duty or some combination of both made them stay.

From the shadows came a large figure. Muichirō had expected something feral, animal-like. Instead, what emerged looked like an ordinary woman with long, unkempt raven hair. Were it not for the writhing shadow writhing behind it, it might have given even him a moment's pause.

"What's wrong?" the demon said, moving towards the man, one hand outstretched. "Don't you recognise me?"

Muichirō’s fingers tightened around the hilt of his sword, but he paused.

The man stopped shaking. He looked up at the demon, tears streaming down his face, and instead of pulling away, he let it touch his cheek. A smile broke across his lips.

He could feel the confusion radiating from the three Kakushi, and beneath it, the unspoken question: why aren’t you doing anything?

Why indeed. Curiosity, perhaps. He was meant to observe before acting and report back what he found, although in practice that was Ginko's duty, given how unreliable his memory was. And besides, it was one man. He didn't appear to be anyone significant. If he died in the course of gathering information, nothing of consequence would be lost.

"Sui…" the man breathed, pressing his face into the demon's hands. "How… how are you alive?"

Ah. So the reports were accurate. The demon had taken the face of someone this man had loved. A wife, judging by the way he kissed its hands. Or someone equally close.

It made Muichirō frown. Why were humans so willing to be deceived? If his wife were dead, what did he think had happened? That she had simply returned?

"I'm sorry for leaving you," the demon said softly, drawing the man into its arms, his head against its chest. "I didn't know how much pain you were in."

If she were allowed, Ginko might have screeched at the blatant trickery. Muichirō, however, had seen enough.

In a single, blurred leap, he cleared the distance. Before the demon could tighten its grip, his blade hissed through the air. The demon’s arms flew upward, severed, as a brilliant arc of blood sprayed across the pavement.

The demon’s scream should have brought Muichirō satisfaction, but the scent emanating from the wound made him pause. He knew instantly that this wasn’t the main body; through a Blood Demon Art, it had manifested a mere shell.

He scanned the shadows. Perhaps he should have remained hidden and observed longer. Sure, the man would have died, but that was just one life. However, since he had already revealed himself, he might as well finish it.

“What have you done? You hurt my Sui!” The man scrambled up, eyes blazing and fists clenched. He was drenched in sweat, his breath coming in ragged hitches. “Apologise to her!”

Strange, Muichirō thought. Despite the man’s explosive emotion, his gaze remained glazed. If he were just being tricked, he would have rushed to this "Sui" to stem the bleeding. Instead, he was charging at a Hashira.

Hypnosis. Muichirō sighed. Why did humans always have to complicate his missions?

“Don’t hurt him, my love. I can take care of myself,” the demon purred. In a sickening blur of flesh, its severed limbs knitted back together.

“But Sui—”

“I said I can handle it!” The demon flung the man aside with a backhanded strike. Had Muichirō not moved, the man would have been crushed against the nearby stone wall.

Using Total Concentration Breathing to bolster his speed, Muichirō caught the man mid-air. He concentrated his breathing into his arm, swept it around the man's waist, and killed the momentum.

He swiftly carried him back to the three Kakushi. “Get him out of here,” he commanded.

Lady acted without hesitation, pressing two fingers to the pressure point at the man’s neck, which caused him to go limp. Whether he would remember any of this by morning was irrelevant.

Muichirō turned back to the demon, sword ready, when it spoke again.

“I never thought we would meet again." Its voice had softened into something almost wistful. "It's a shame our reunion had to happen somewhere so unworthy of us.”

Muichirō didn’t respond. He wouldn’t allow an inferior creature to ruffle his composure. Above him, Ginko let out a sharp scoff.

“Ginko, leave,” he ordered. This should be an easy fight, but he wanted her out of the crossfire. The crow hesitated, her worry palpable, but she eventually took flight.

“You still have her? Crows do indeed live for a long time.” A faint, haunting longing traced the demon’s tone. For a heartbeat, its form flickered, settling into the shape of a woman. Its hair smoothed and gleamed, black and silky. Its lips deepened to red. An elaborate kimono replaced the rags, and a pin with ginkgo motifs appeared at its temple. It had become the most beautiful woman Muichirō had ever seen.

Something stirred in Muichirō’s chest. Had he met someone who looked like this image? He must have; the demon wouldn't have chosen this face otherwise. But who had she been to him?

It doesn’t matter, he told himself. He had no memory of her, and he would not let a phantom stay his hand.

“Mist Breathing, Second Form: Eight-Layered Mist.”

Ignoring the gnawing need for answers, he drove eight slashes into the demon. To his surprise, the demon didn’t evade. Instead, it surrounded itself with large shards of mirror that materialised from nowhere, and every strike landed on glass instead of flesh. The shards shattered, but was that enough? This wasn’t even the demon’s main body.

He had to end this. 

“Mist Breathing, Fifth Form: Sea of Clouds and Haze.”

He shifted his grip, focusing his strength into his legs to deliver a high-speed, zig-zagging assault. But the demon transformed again. This time, it took the shape of a man.

He was majestic, a warrior of immense stature. His long, spiky black hair was tipped with red and tied in a high ponytail. His purple eyes were intense yet unnervingly calm. His purple nagagi kimono spoke of high status, but it was his presence that struck Muichirō.

Muichirō’s knees trembled. Deep within his subconscious, a primal terror collided with a lingering sense of awe. His breathing became frantic; his heart hammered against his ribs like a trapped bird. His blood seemed to hum in recognition.

Who is he? Why am I—

Muichirō closed his eyes and took a deep, steadying breath. No. Regardless of who this man had been, he would not be a puppet to a demon’s tricks. He was a Hashira. It was his duty to slay demons, not to be paralysed by memories that refused to surface.

“Mist Breathing, Third Form: Scattering Mi—”

“Stand down, my child.” The deep, resonant command chilled Muichirō to his marrow.

Muichirō realised he had been too arrogant. He had judged the hypnotised man for his weakness, but now he found himself in awe of a face he didn’t even recognise, his soul vibrating with a terrifying respect. Someone from his past had looked like this; whoever this man had been, he had left an impression so deep that not even the loss of Muichirō's memories had erased it.

But as the fear peaked, a cold, sharp clarity settled over him.

“You should put your sword down and come to me,” the demon said.

That command snapped Muichirō out of his reverie. Yielding was not in his nature. A new emotion surged, intense as erupting lava, dizzying and hot. It made his vision sharpen to a point.

“Mist Breathing, Sixth Form: Lunar Dispersing Mist.”

He leapt higher than his own height, soaring over the rooftops surrounding the plaza. When his blade met the demon, he cut without hesitation. Surprise crossed the demon’s face, and a part of his mind recoiled from the sight. He would never have looked like that.

As Muichirō landed, the demon’s body split vertically, beginning the slow crumble into ashes.

“I thought it would make you hesitate,” the demon rasped, its voice dissolving with the rest of it. “I thought I could finally talk to you again. Why... Why would you strike your own family? I thought you loved him...”

It was a demon, so of course it was lying. That was the only logical conclusion. Yet, Muichirō’s heart ached with a truth his brain couldn't process. The hatred in his chest burnt hotter.

"Perhaps," Muichirō said to the ash and the empty plaza. "I don't remember him. If he exists, I’ll kill him myself." He watched the last of the ash scatter. "Don't ever take his face again.”