Demon Slayer: Dragon Hashira#1+2+3: Yukimura Kaidō, A New Identity, The Kamado Family

Hey everyone!

I hope you’re having a wonderful day. The new fanfic is finally here! If there’s anything that needs tweaking, please let me know. For now, just sit back and enjoy!

As usual, I’ll be doing a bulk upload of this fanfic this weekend. I’m also on the lookout for some great fanfics, like Naruto, for example. If I find anything good, you’ll see it here!

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"I will fulfill my duty! No one here is going to die!"

"Flame Breathing, Final Form!"

"I am the Flame Hashira, Kyojuro Rengoku!"

"Ninth Form: Rengoku!"

"Destructive Death: Annihilation Type!"

"Rengoku-san!"

"Ring ring ring—incoming call!" A long white-haired young man sat hunched in front of his computer, a lollipop tucked in his cheek. He glanced at his phone screen—the caller ID read "Mom"—and hit the spacebar to pause the anime before answering.

"Hey sweetie, I'm getting off my morning shift soon and picking up your sister. Could you run to the market and grab some groceries for dinner? You know Reika absolutely loves your cooking!"

My adoptive sister's name is Reika. She's about to graduate middle school—hard to believe it's been almost ten years since she joined our family. That crying little girl who first walked through our door has grown into a beautiful young woman.

If it weren't for my sister and that one close friend of mine helping me through everything, I'd probably still be that pathetic, confidence-lacking coward I used to be.

"Sure thing, Mom. I'll head out in a bit. You and Reika be careful on your way home, okay?"

"Will do! Um, honey... you'll be alright on your own, won't you? I mean, considering your—"

"I'm fine, Mom. It's been years. I'm used to it by now."

"Alright, that puts my mind at ease. Just be careful out there too!"

"Got it, Mom!" After hanging up, I shut down my computer and grabbed my jacket.

The moment I reached for the door, my phone rang again.

"Ring ring ring!!" The second I heard that ringtone and saw "Monkey" flash across the screen, I knew exactly who it was. I couldn't help but crack a smile as I hit accept.

"Hey, Monkey. What's up?"

The voice on the other end immediately erupted: "Damn it, did you change my ringtone again??"

Monkey's real name is Hayato. He's got the most straightforward personality you'll ever meet, and he's one of the very few people I consider a true friend.

Back in middle school, I was the quiet kid who barely spoke. Add in my feminine features and timid personality, I became an easy target—bullying, mockery, even beatings. I took it all in silence, never fighting back, just enduring it all. Hayato was the only one who treated me like an actual friend, always having my back.

Because our personalities were complete opposites, we somehow clicked. We'd game together on holidays, hit up barbecue joints for grilled skewers. Hayato knew my family situation, so he'd always snatch the bill before I could even reach for my wallet.

Eventually, I realized Hayato wasn't like everyone else. He genuinely saw me as a friend.

Then came the incident—a school violence situation that cost me my left eye and forced me to drop out before even finishing middle school.

"Anyway, forget all that. You free tonight? Wanna squad up? And get this—I've got two cute gamer girls joining us! Hehe, hehehehe! ( ͡° ͜ʖ ͡°)"

"I can smell the desperation from here. What kind of perverted fantasies are you cooking up now?"

"Hey, I'm a refined gentleman with impeccable taste! Besides, these girls are just a little lonely, and I'm simply offering them a place where they belong! ( ´ ▽ ` )"

"(ಠಠ) You shameless bastard, you're just thirsty as hell. Whatever—I don't have time for this. I need to grab groceries and make dinner. Can't make it tonight. Just watch yourself out there. I heard the organ traffickers up north are running low on kidneys!"

"Come on, I'm not thirsty—I'm just giving them a home! Fine, if you're busy, we'll do it next time. Guess I'll have to comfort these two lonely hearts all by myself tonight! (˘ω˘)" After chatting a bit more, we hung up.

I stepped outside and walked for a while until I reached a traffic intersection. The light turned green, and that's when I saw it—a small truck, completely out of control, barreling through the red light straight toward a woman crossing the street.

"Watch out! GET OUT OF THE WAY!" But it was already too late.

The truck closed the distance in seconds. Without thinking, I lunged forward and shoved the woman out of harm's way.

The impact sent me flying dozens of feet through the air. My head slammed against something hard—the world blurred, and through the haze, I could barely make out the woman I'd saved running toward me...

"Stay with me! The ambulance is almost here! Don't fall asleep—whatever you do, don't close your eyes!"

...

Several hours later, inside the hospital.

"Doctor, how is he??"

The doctor's expression said it all. "I'm sorry. We did everything we could. His head trauma was severe, and his lung was punctured. He won't make it through the night."

"What?? That's impossible! Doctor, isn't there anything else you can do?"

"If there were another way, I’d do everything I could to save him. But... he doesn't have much time left. You should go see him. He seems to have something he wants to say to you. If you can... spend these final moments with him."

The woman's voice came out hollow. "I understand. Thank you, Doctor."

...

Inside the hospital room, she stared at the young man who'd saved her life—now lying in a bed, never to see another sunrise. Her heart twisted like a knife was carving through it.

"Cough cough... Hey there. Could you... cough... tell me your name?"

"My name is Tachibana Sumiko. What's yours?"

"I'm Yukimura Kaidō. Cough cough..."

"You seem like... someone important. Sumiko-san, could you... cough cough... do a few things for me?"

"Tell me. Whatever you need—if it's within my power, I'll make it happen."

"Thank you, Sumiko-san. Please... tell my mother... I'm sorry for all the trouble I caused her. I never got to... fulfill my duty as her son. I've saved up some money over the years—it's in the drawer... under my computer desk. Please tell her to use it... to take care of herself and my sister. And... tell my sister that her brother was useless... I couldn't protect her the way I promised. I won't get to see her... in a beautiful white wedding dress... walking down the aisle. Finally... cough cough..."

"Stop—don't talk anymore! You need to rest. The doctor said you need rest to recover." Sumiko's voice cracked with urgency.

"I know what's happening to me. You don't need to hide it."

"One last thing... tell my best friend I'm sorry... I can't keep gaming with him anymore. And I hope... he doesn't end up like his old man... always in the doghouse..."

"Alright, I promise. Everything. Now please, just stop talking and rest."

BANG!

The hospital room door burst open.

"Brother! Are you okay?? Please don't scare me!" Reika gripped her brother's hand tightly, her eyes swimming with worry and fear.

"Kaidō, how are you feeling? Tell me if anything hurts! This is all my fault—if I hadn't asked you to go out, this never would have happened!" His mother looked at her son, heartbreak written across her face.

"Mom... Reika... I'm sorry." A single tear rolled down his cheek before his eyes closed...

"LIAR! You're such a liar, big brother! You promised to protect me—you promised you'd marry me! Why did you lie?? Wake up right now, or I'll never forgive you—never!" Reika sobbed.

"Doctor! Doctor!" His mother's desperate cries echoed into the hallway...

"Don't worry. I, Tachibana Sumiko, will take care of your family. I won't let them suffer—I swear it." Sumiko's silent vow hung heavy in the air.

...

[Ding! Compatible transmission target detected. System binding initiated... Binding successful!]

[Constructing transmission space... 10%... 30%... 60%... 100%... Construction complete. Initiating transmission... Transmission in progress... Transmission successful...]

[Ding! Host detected in soul state during dimensional transfer. Reconstructing physical body... Reconstruction complete. Initiating soul fusion... Fusion successful! Host detected in weakened state. Transferring host to safe location!]

[Ding! Transfer complete!]

[Ding! Creating new identity for host... Identity creation successful!]

[Beginner's Package has been placed in System Space. Host may open upon awakening!]

"Hey, miss! Wake up! Are you okay? Come on, wake up!"

"Big brother, I think she passed out. We should take her home—there's so much snow falling. We can't just leave her here!"

"Yeah, let's carry her back together."

"Who are they? Where am I??" The thoughts flickered through Kaidō's fading consciousness, but the fog was too thick—he couldn't voice them aloud.

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"Big brother, is the white-haired miss still unconscious?"

"Yeah, it's been almost two days now. There aren't any wounds on his body, so he probably went through some kind of shock—that's why he hasn't woken up yet. And Nezuko, he's a guy, not a girl!"

"Wait, what?? Σ(￣□￣lll) Are you serious, big brother?? But he looks exactly like a girl!" Nezuko glanced at the white-haired young man lying on the tatami mat—delicate features, long white hair, and an elegant white robe accented with crimson.

"I'm sure. I could tell by scent, and Mom found out when she was adjusting his clothes..." Tanjiro's face flushed red as he trailed off.

When he first saw this white-haired person, he'd thought it was a girl too. He'd even asked Nezuko to help wipe his face with a hot towel...

Wait. The realization hit him like a lightning bolt, and Tanjiro whipped around to face his sister. "Nezuko, when you were wiping his face with that hot towel earlier, you didn't... you didn't..."

Nezuko: "Didn't what?"

"You know... you didn't wipe anywhere else, right??"

Nezuko: "Anywhere else? No, I just wiped his face. Big brother, what other places are you talking about?" Her confusion was genuine at first, but then her mind caught up.

Other places? Besides his face, that would mean...

The moment she understood what her brother was implying, Nezuko's face turned beet red.

Even someone as innocent as Nezuko could figure out what he meant.

"Big brother, you're terrible!" Nezuko puffed out her cheeks indignantly, glaring at him.

"No, that's not—I didn't mean it like that! What I meant was—"

"Tanjiro, Nezuko, has the child woken up yet?"

Tanjiro and Nezuko: "Mother."

The person who entered was Kie Kamado, mother to the siblings.

Tanjiro: "Not yet, Mother. I think he experienced some kind of trauma, which is why he's still unconscious."

Nezuko: "Mother, big brother was being awful! He asked me if I'd..."

"If you'd what?" Kie asked.

"He asked if I'd... if I'd..." Nezuko's voice grew quieter and quieter. Just thinking about what her brother had implied made her too embarrassed to finish the sentence.

"Alright, Nezuko. Tanjiro didn't mean anything by it. Why don't you both go get ready—dinner will be ready soon." Kie gently patted Nezuko's head.

Nezuko: "Okay."

Tanjiro: "Understood."

...

"Where... am I?" Kaidō's eyes slowly opened as he sat up, taking in his surroundings. A wooden house, simple yet warm.

Something about this place felt strangely familiar, though he couldn't quite place why.

[Ding! Host, you're awake.]

"Who's there?? Who's talking to me??"

[Host, I am the Demon Slayer System. I exist within your consciousness. You can communicate with me mentally through your thoughts.]

"Demon Slayer System? You're... a system?" Understanding dawned on Kaidō instantly. He'd read plenty of web novels before—he knew systems were essentially golden fingers for transmigrators.

"Systems are standard equipment for anyone who crosses worlds, which means that I'm... wait a second!"

He immediately addressed the system mentally. "System, wasn't I already dead?"

[Correct, Host. You died on Earth. Your mother and adoptive sister have already held your funeral.]

"Then what's going on with this body? I feel perfectly fine."

[Because Host arrived via soul transmigration, this body was reconstructed by the system. However, it functions identically to a normal human body and requires training to strengthen. Your soul was weakened during the fusion process with your new body, which is why it took nearly two days to complete.]

[Additionally, the reconstructed body is identical to your original form from when you were alive.]

...

After spending some time communicating mentally, Kaidō finally understood what this [Demon Slayer System] was all about.

His soul had been transported here through an interdimensional gateway constructed by the system. This world was the Demon Slayer anime he'd watched countless times back when he was alive.

The Demon King Muzan Kibutsuji, who created demons to search for the Blue Spider Lily in his quest to become the perfect, ultimate being.

In a world overrun by demons, there existed an organization called the Demon Slayer Corps—an entity not officially recognized by the government, though they frequently collaborated behind the scenes.

The system had also created a new identity for Kaidō in this Demon Slayer world—Ryūjin Kaidō.

"Listen, System, couldn't you have given me a better surname? 'Ryūjin' sounds like something out of a bad edgelord fantasy."

[Ding! This name was selected based on games the host played while alive. If Host dislikes it, the system can modify it. Based on anime you've watched, such as your favorite character Kurumi Tokisaki, or Kasuga...]

"Stop, stop, stop! If you keep going, everyone's going to start making weird faces. Fine, Ryūjin Kaidō it is."

Yukimur—no, Ryūjin Kaidō—accepted the name without further argument.

System: ???

Kaidō: "...This feels weird."

[Host, you still have an unclaimed Beginner's Package. Would you like to claim it?]

"Beginner's Package? Yeah, claim it."

[Ding! Congratulations! Host has received: Body Enhancement Serum x1, Total Concentration Breathing: Constant, Dragon Breathing First Four Forms, and 100,000 Yen.]

The Body Enhancement Serum was self-explanatory—it strengthened the body, improving physical attributes and resilience.

Without hesitation, Kaidō drank the serum. A warm sensation spread through his body, a current of heat flowing through his abdomen. Within moments, he could feel power coursing through every fiber of his being.

Total Concentration Breathing: Constant was one of the prerequisites for becoming a Hashira. He hadn't expected to already possess the ability to maintain the breathing technique twenty-four hours a day.

"Dragon Breathing First Four Forms?" Kaidō examined the breathing technique's name.

Dragon Breathing, First Form: Dragon's Breath — Upon activation, dramatically enhances all attributes including attack speed, movement speed, attack power, and strength. The enhancement scales with the user's own capabilities.

Dragon Breathing, Second Form: Dragon Claw — Single-target attack. Leap into the air and strike downward with a vertical slash, tearing through the enemy like a dragon's claw.

Dragon Breathing, Third Form: Divine Dragon's Tail — A forward horizontal slash creating a wide fan-shaped area of effect, sweeping away all enemies in front like a dragon's tail.

Dragon Breathing, Fourth Form: Coiling Dragon — Use your weapon to guard defensively, creating a protective barrier centered on yourself, blocking attacks from all directions like a dragon coiled around a mountain.

Kaidō also discovered that the First Form could be stacked with the other forms, though he'd need to test it himself to understand the full effects.

"The system only released the first four forms. Looks like I'll have to develop the later forms on my own. Wonder what they'll be like?"

"As for the 100,000 yen, in this world that makes me practically a small-time tycoon—enough to change the circumstances of several families."

"Ah, you're awake! Father, Mother—the white-haired person woke up!" Nezuko called out to her parents.

Several children and two adults entered from outside. Though Kaidō had already confirmed certain things in his mind, seeing them in person still caught him off guard.

"You're awake, child. How are you feeling? Is there anywhere uncomfortable?" Kie Kamado asked gently.

"Big brother, you finally woke up!"

"Who are you people? Where am I?"

"My name is Kamado Tanjiro. This is my sister, Kamado Nezuko, along with Hanako, Takeo, Shigeru, and Rokuta. This is my father, Kamado Tanjuro, and this is my mother, Kamado Kie."

"My sister and I found you collapsed in the snow in the mountain forest, so we carried you back. You've been unconscious for nearly two days," Tanjiro explained.

"My name is... Ryūjin Kaidō. Thank you for saving me."

(PS: Kaidō is quite similar to Rimuru Tempest, except with white hair!)

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"Thank you for saving me. My name is Ryūjin Kaidō."

Nezuko: "Ryūjin Kaidō... what an unusual name!"

Tanjiro: "Nezuko, don't be rude!" He turned back quickly. "I apologize—my sister can be a bit blunt. Please don't take offense."

"None taken. Your sister's adorable. I like her." Kaidō's smile was genuine.

Watching Nezuko kneeling beside him, Kaidō couldn't help but reach out and gently pat her head, murmuring almost to himself, "If only my sister were here too... but I've already..."

The gesture caught Nezuko off guard—her face flushed red, though she didn't pull away.

Tanjiro's nose picked up a wave of melancholy emanating from Kaidō, but underneath it lay something else—something he couldn't quite identify or put into words.

"Sorry, I didn't mean to make things awkward." Kaidō withdrew his hand quickly.

"If you don't mind, you're welcome to stay with us for a while," Tanjuro Kamado said with a warm smile.

"Yes, please stay! The children seem to have taken quite a liking to you already," Kie added.

Takeo: "Yeah, big brother! Stay with us! You can play with us, and I want to hear your stories!"

Hanako: "Please stay! Your hair is so long and beautiful—can you teach me how to style mine like that?"

...

Kaidō looked at the family surrounding him, their voices overlapping with genuine warmth. Something deep in his chest loosened. "Thank you all—Tanjuro-san, Kie-san, Tanjiro, Nezuko, Hanako, Takeo, Shigeru, Rokuta. I'll be in your care for a while."

Despite their simple lifestyle, the Kamado family radiated warmth.

His thoughts drifted to his own mother and adoptive sister, to his best friend Hayato. How are they doing now?

...

Seven days passed living with the Kamado family. During that time, Kaidō maintained a careful routine—aside from daily life with the family, he carved out time each day to practice Dragon Breathing, steadily increasing his proficiency.

He often helped Tanjiro chop wood and make charcoal, occasionally joining him on trips down the mountain to sell their wares.

While Kaidō could easily give them money to improve their situation, he knew their humble, honest nature wouldn't allow them to accept it.

So instead, he helped with their work and sometimes brought back treats for Nezuko and the younger children after selling charcoal with Tanjiro.

When Kie tried to refuse, Kaidō simply said, "The children are still growing. Better food will help them develop properly."

Tanjiro: "Kaidō-san, you're not really that much older than me, are you?"

Kaidō: "I'm thirteen—two years older than you. Doesn't that make me your older brother?"

'If you knew my actual age from my previous life was twenty-five, I'd be your uncle, not your older brother.'

Thank god for the system creating a new body for him.

But that wasn't even the worst part. Why did the system have to shrink him when it reconstructed his body?

'In my previous life, I was at least five-foot-nine. Now? I'm stuck at barely five feet. I swear the system did this on purpose. System, you're on my list...'

System: [Host, I can hear you. Host has a thing for lolis.]

Kaidō: "..."

System: [Host collected numerous loli posters.]

Kaidō: "(ಠ_ಠ)"

System: [Host's computer contained...]

Kaidō: "You know what? This height is perfect. No need to change it. Besides, modifications always come with a price, so let's just leave it as is!"

System: [As long as Host is satisfied.]

Kaidō: "(¬_¬|||)"

Tanjiro: "Kaidō-san, are you alright? You look pale—are you feeling sick?"

"I'm fine, really. Just remembering something from the past. Don't worry about it—it's getting dark. We should head back. Nezuko and the others are probably waiting for us." Kaidō quickly changed the subject.

Though Tanjiro found the exchange odd, he didn't press further. The sky was indeed darkening, and once night fell, wild animals would emerge from the mountain forests to hunt. Better not to risk it. Without another word, he hurried to catch up with Kaidō.

.....

Time passed swiftly. Before long, Kaidō had been living with the Kamado family for half a month.

During this period, the system hadn't issued a single task or given any notifications—as if it had fallen dormant. But Kaidō knew better. The system was never that simple.

"Over the past two weeks, I've been practicing Dragon Breathing whenever I could. I've successfully developed two new forms."

Dragon Breathing, Fifth Form: Violent Tempest — Rapidly swing the blade forward, unleashing a barrage of sword strikes. The sheer brutality of consecutive slashes depends entirely on the user's strength and can generate anywhere from dozens to hundreds of blade projections.

"At my current level, I can unleash about fifty sword projections. If I stack it with the First Form, I can push it to nearly ninety."

Dragon Breathing, Sixth Form: Tornado Maelstrom — Area-of-effect attack. Spin rapidly with yourself as the center point, creating a vortex of blade energy through high-speed rotation. (Think of it like Yuzuru's technique from Date A Live.)

"According to the timeline, Tanjuro dies when Tanjiro turns twelve—roughly six months from now. The Final Selection on Mount Fujikasane happens once a year, which means I have less than five months left to prepare."

Kaidō's internal monologue took on a darker, more analytical tone.

"I know how the story is supposed to unfold, but if I intervene carelessly and alter the plot, I might trigger a butterfly effect—leading to an entirely different outcome."

His mind turned to the tragedy awaiting the Kamado family.

"One year after Tanjuro's death, the Kamado family is attacked by Muzan Kibutsuji. But I've always had doubts about that."

The question gnawed at him like an itch he couldn't scratch.

"Was it really Muzan who slaughtered Tanjiro's family? Given Muzan's cowardly, paranoid nature, would he truly risk attacking the Kamado household personally?"

The circumstances of their deaths had always struck Kaidō as strange.

When Tanjiro returned home, he found only corpses—no signs of consumption. Ordinary demons wouldn't leave bodies behind. They'd devour everything.

And why does everyone assume it was the Demon King just because Nezuko turned into a demon?

Muzan had no logical reason to target this specific family. He typically operated in bustling urban centers, not isolated mountain villages. If he were hunting down the inheritor of the Sun Breathing technique, he would have learned about it through his subordinates—yet not a single demon throughout the entire story ever mentioned Muzan being responsible for the massacre.

If revenge were his motive, he'd be searching for the wielder of the Hanafuda earrings. Given Muzan's paranoid nature, he'd only strike after confirming the location of the Sun Breathing user. Barging into the Kamado residence on a whim wasn't his style.

Furthermore, Kokushibo—Upper Rank One—had explicitly stated that he and Muzan had already eliminated all known descendants of Yoriichi Tsugikuni's breathing techniques. In Muzan's mind, there should have been no one left to take revenge against.

Another detail stood out: all the Kamado family members were left as whole corpses.

When Muzan killed—whether human or demon—he never left intact bodies. During the purge of the Lower Ranks, every demon except Enmu was obliterated without a trace. When a servant discovered Muzan wasn't human, that person was instantly reduced to pulp.

Why would such a violent, brutal entity leave every single victim as a whole corpse?

So who was the real culprit?

Whoever it was possessed the ability to create demons—meaning they had access to Muzan's blood, and not just a small amount. They had combat capabilities far beyond normal humans and could replicate the attack patterns of demons.

Who fits these criteria?

After eliminating Muzan as a suspect, Kaidō's mind sifted through the possibilities: the Twelve Kizuki, Tamayo, or—however absurd it seemed—the Demon Slayer Corps itself.

The Twelve Kizuki could be ruled out first. While they possessed the ability to create demons, they lacked motive. Creating demons required Muzan's explicit approval, and since Muzan remained unaware of Nezuko's existence, they were off the list.

Tamayo could also be eliminated. She had been turned into a demon by Muzan without her knowledge, devouring her own husband and children in the process. Her hatred for Muzan ran bone-deep. Had she not encountered Yoriichi Tsugikuni, she never would have escaped Muzan's control.

While Tamayo could transform humans into demons, she always asked for consent first—as she had with Yushiro. She was a demon fighting for humanity's sake. There was no way she'd slaughter an innocent family.

That left the third possibility.

The Demon Slayer Corps.

The very idea seemed ludicrous. Demon slayers and demons were supposed to be mortal enemies, sworn to destroy each other. But even if the probability was one in ten thousand, it wasn't impossible.

Because in Kaidō's eyes, the circumstances surrounding the Kamado family's deaths were far too suspicious to ignore.