Demon Slayer: Dragon Hashira#13/16: Fighting Three Hashira, I Am the Dragon Hashira, Kaidō's Identity, and a Very Sus System, Demon Slayer Mark & Its Side Effects, Kaidō's Demon Training Regimen

"The Master has arrived."

A young man emerged, supported by the two white-haired girls. As he stepped under the eaves, Kaidō finally got a clear look at him—Kagaya Ubuyashiki, current leader of the Demon Slayer Corps.

The Master whom all the Hashira served had severe facial disfigurement above the cheekbones, and both eyes were blind. In his youth he'd been handsome, but progressive illness had gradually ravaged his features.

The same disease left him constitutionally frail—he couldn't even swing a sword ten times. Yet he possessed natural leadership qualities and a magnanimous heart, speaking with calm warmth and treating everyone with courtesy.

His voice and the rhythm of his movements had a way of putting people at ease—a gift possessed only by those capable of moving the masses.

He valued his subordinates deeply, memorizing the life story of every fallen Demon Slayer. Before his condition deteriorated to the point where he could no longer walk, he'd visited the graves of fallen Corps members daily.

Every member of the Demon Slayer Corps respected him like their own father—even the hot-tempered Wind Hashira, Sanemi Shinazugawa.

"Good afternoon, my beloved children." Kagaya's voice had an almost hypnotic quality that lifted the spirits of everyone who heard it, making their heads feel light and pleasant.

'So this is Kagaya Ubuyashiki. His voice really does have that effect—makes you feel relaxed, almost floaty.'

"Hey! You bastard—why aren't you kneeling before the Master??" Sanemi's roar shattered the peaceful atmosphere.

Kaidō simply bowed slightly at the waist. "My apologies. My family's teachings forbid kneeling to anyone—we only kneel to our parents. I hope you'll understand."

"You piece of—" Sanemi started forward, fists clenched.

Kagaya raised his left index finger to his lips, signaling for silence.

Sanemi froze mid-step and dropped to his knees, though fury still radiated from every line of his body.

"I understand. I've told my children they don't need to do this, but they kneel of their own free will, so I respect their choice. Just as I respect yours." Kagaya's tone remained gentle. "After all, my ancestors had dealings with your family. I'm aware of your traditions."

"Thank you." Kaidō bowed again in gratitude.

The system must have connected my new identity to the Ubuyashiki clan's history. That works out—at least my background is covered.

"Today's Hashira meeting has a single purpose: I wish to make Ryūjin Kaidō the tenth Hashira, and I hope all of you will recognize him."

"I refuse." Sanemi was first to object. "I won't acknowledge anyone who doesn't respect the Master."

"I don't care either way. I'll forget about this soon anyway." Muichiro's tone was completely flat.

"I'll follow whatever the Master decides!" Mitsuri chirped.

"Either way works for me." Giyu's contribution was characteristically minimal.

"If he can prove his strength, I'll recognize him." Rengoku's voice boomed across the courtyard.

"Exactly! As long as he can flamboyantly demonstrate his abilities!" Tengen agreed enthusiastically.

Rengoku's proposal won unanimous support.

Kagaya turned toward Kaidō. "The Hashira of the Demon Slayer Corps possess formidable strength, earned through hellish training and countless battles. The choice is yours. Whatever you decide, I will respect it."

"I accept the proposal. No objections."

"Good! Then I'll go first. Listen up, kid—becoming a Hashira isn't some walk in the park. I won't be holding back!" Sanemi stepped forward as the other Hashira retreated, leaving ample space for combat.

Several meters separated the two fighters. Kaidō lowered his fox mask over his face—the gesture had become habit by now. He shifted his right foot forward slightly, right hand gripping the greatsword on his back, settling into combat stance.

Sanemi's left hand closed around his scabbard, right hand on the hilt. Battle-ready.

"Wind Breathing, First Form: Dust Whirlwind Cutter!"

Sanemi exploded forward in a high-speed assault, leaving rotating wind blades in his wake—blades sharp enough to carve through solid ground. The attack came with a devastating shockwave.

Kaidō's response was immediate. He drew his greatsword.

"Dragon Breathing, Second Form: Dragon Claw!"

He launched himself upward, bringing the blade down in a devastating vertical slash—like a dragon's talon striking prey.

Since this was only a sparring match, Kaidō didn't stack the First Form enhancement.

"SHIT—!" Sanemi felt the power behind that strike and immediately raised his blade to block.

But blocking it completely was impossible. Kaidō's greatsword weighed over a hundred pounds. He'd consumed two Body Reinforcement Serums and trained relentlessly in his spare time. His current strength was several times what it had been.

BOOOOOOOOOOOOOOOOOM.

Sanemi flew backward, feet carving furrows dozens of meters long across the courtyard. But years of combat experience kicked in—he recovered quickly, already adapting.

"Wind Breathing, Eighth Form: Primary Gale Slash!"

He surged forward and spun around Kaidō in a circular slashing motion, unleashing a powerful spiral of wind blades designed to shred the target from all angles.

"Dragon Breathing, Seventh Form: Eight-Directional Blitz!"

Kaidō became a whirlwind, his greatsword carving through the air with blinding speed. Eight separate blade projections shot outward simultaneously, nullifying Sanemi's attack.

Each projection carried significant destructive force. After canceling the Wind Breathing technique, they continued expanding outward, forcing Sanemi to abort his advance and leap backward to escape their range.

"What a flamboyant guy—he's actually matching Sanemi blow for blow. Hell, he's got the advantage!" Tengen watched the exchange with obvious appreciation.

"Do I even deserve to be called his senpai?" Giyu muttered to himself.

"Wind Breathing, Fifth Form: Cold Mountain Wind!"

A wide-area attack—massive rotating wind blades launched from above. Sanemi had once used this technique to counter Giyu's Water Breathing Seventh Form.

After countless exchanges, Sanemi was getting frustrated. He unleashed this large-scale assault directly at Kaidō.

"Sanemi, are you insane?? STOP!" Tengen shouted.

"Dragon Breathing, Fourth Form: Coiling Dragon."

Kaidō immediately switched to a defensive technique. He gripped the sword handle with both hands, planting the blade's tip into the ground. A translucent barrier formed around him, blocking the attack completely.

Then, without missing a beat: "Dragon Breathing, Third Form: Divine Dragon's Tail!"

The horizontal slash expanded into a massive fan-shaped wave of cutting force—like a dragon's tail sweeping everything before it.

Sanemi flew backward again, hitting the ground hard. His Nichirin blade shattered from blocking Kaidō's strike.

Defeated...

"What's the situation?" Kagaya asked.

"Shinazugawa-sama couldn't block Kaidō-sama's attacks. He's been defeated." Hinaki Ubuyashiki reported.

"Thanks for the match." Kaidō drove his greatsword into the ground and walked over to Sanemi, extending his hand to help him up. He bowed apologetically.

"Hmph." Sanemi grabbed Kaidō's hand and pulled himself upright. He wasn't happy about losing, but he'd acknowledged the kid's strength. He rejoined the other Hashira without another word.

"Young man, you're strong! I'd like to test myself against you as well!" Rengoku stepped forward, voice booming with enthusiasm.

"Let's do it."

Perfect—the system quest required defeating any three Hashira. Rengoku would be number two. He'd figure out the third opponent afterward.

They established distance. Kaidō drew his greatsword, gripping it with both hands. Rengoku's hand moved to his hilt, settling into stance.

After several seconds of eye contact, Kaidō attacked first.

"Dragon Breathing, Eighth Form: Serpent's Pierce!"

He charged straight forward, greatsword cutting through the air in rapid succession, unleashing blade projections. To the watching Hashira, it looked like a serpentine dragon launching itself forward—unstoppable momentum given physical form.

"Flame Breathing, Fifth Form: Flame Tiger!"

Rengoku thrust forward, his strike taking the shape of a burning tiger—massive and devastating.

CLANG!

Their weapons collided. The shockwave exploded outward, forcing even the Hashira to brace themselves.

They all knew Rengoku's strength intimately. Among the nine Hashira, he was second only to Stone Hashira Gyomei Himejima.

Yet here was someone—a rookie who'd joined the Corps less than a month ago—matching Rengoku blow for blow without losing ground.

Clang! Clang! Clang!

Steel rang against steel in a relentless rhythm.

"Flame Breathing, First Form: Unknowing Fire!"

Rengoku dodged Kaidō's strike, leapt backward, then rocketed forward with explosive speed—closing the distance in an instant to deliver what should have been a finishing blow.

"Dragon Breathing, Sixth Form: Tornado Maelstrom!"

Kaidō spun with his greatsword extended, becoming a human cyclone. Tornado-like blade projections spiraled outward from his position.

"Flame Breathing, Fourth Form: Blooming Flame Undulation!"

Rengoku immediately adapted mid-strike, switching techniques. He spun in place, unleashing a vortex of flame slashes designed to counter wide-area attacks.

The battle intensified. Kaidō showed no signs of fatigue—if anything, the fire in his eyes burned brighter with each exchange.

This was exactly the kind of experience he needed. When he eventually faced powerful demons, he wouldn't be helpless.

But the system quest demanded completion. Time to end this.

"Dragon Breathing, Second Form: Dragon Claw!"

The downward strike came too fast to dodge. Rengoku had no choice—like Sanemi before him, he raised his blade to block.

BOOOOOOOOOOOOM!

Rengoku flew backward, feet carving through dirt before he managed to stop himself several meters away. His blade was planted in the ground, and he used it to pull himself upright.

"I've lost! Young man, you're incredibly strong—I recognize you completely!" Rengoku's voice rang out as powerfully as ever, completely unbothered by defeat. He sheathed his sword and stepped aside.

"Senpai, I'd like to spar with you. How about we settle it in one exchange?" Kaidō turned to Giyu.

"Giyu, you're not going to recognize him just because he's your junior, are you? If that's the case, you really are unlikable." Obanai's voice dripped with sarcasm.

"I'm not unlikable..."

Giyu stepped forward, stopping a few meters from Kaidō. He drew his blade. "Show me what you've got, junior brother."

"Let's do this, senpai."

Once again, Kaidō struck first. "Dragon Breathing, Fifth Form: Violent Tempest!"

He swung his greatsword forward in rapid succession, unleashing nearly a hundred blade projections—violent, consecutive strikes, each one carrying significant destructive power.

"Water Breathing, Eleventh Form: Dead Calm."

Giyu's original technique. He entered a state of perfect tranquility, like the surface of still water—and every attack that entered his blade's range was nullified.

Almost all of Kaidō's blade projections were neutralized by Dead Calm. But the sheer force behind them still managed to tear Giyu's uniform in several places.

'As expected of Giyu Tomioka—his self-created Eleventh Form is incredible. It negated almost all my blade projections.'

"I've lost." Giyu sheathed his sword and returned to the formation.

"Thank you for the match." Kaidō removed his fox mask, hanging it from his head.

"What's the current situation?" Kagaya asked.

"Kaidō has defeated three Hashira. His strength has been recognized." Kanata reported.

"Ryūjin Kaidō, my beloved child—you've proven yourself. Will you become the Demon Slayer Corps' tenth Hashira?"

"I will."

"Have you decided on your title?"

"I use Dragon Breathing, which I created myself. So my title is Dragon. I am the Dragon Hashira."

"Then from this day forward, you are the Demon Slayer Corps' tenth Hashira. Your title: Dragon Hashira."

Kaidō bowed deeply. "Thank you, Master. I will use this blade to slay every demon."

The Demon Slayer Corps' tenth Hashira: Dragon Hashira. A swordsman who'd joined less than a month ago.

The Hashira meeting would continue, but Kaidō had exhausted most of his stamina during the three consecutive fights. Kagaya excused him from the meeting, telling him to rest.

"Rengoku-san, could I maybe crash at your place for a day? I don't know where else to go, so..." Kaidō hadn't even finished the sentence before Rengoku's booming laugh cut him off.

"Of course! Come rest at my home, young Kaidō! We'll have plenty of time for more sparring! Hahaha!"

"Oh my, why not come to the Butterfly Mansion instead? After the meeting ends, I can give you a proper examination. I heard you were injured fighting that Lower Rank demon—we should make sure you're healing properly!" Shinobu's smile was as sweet as poisoned honey.

"No problem at all! Young Kaidō, go rest and recover. When you have time, come visit my home—I'll give you a proper welcome! Hahaha!" Rengoku strode off to the meeting, still laughing.

"Well then, I'll have a Kakushi escort you to the Butterfly Mansion."

Shinobu summoned one of the black-clad Corps members before heading to the meeting herself.

"Dragon Hashira-sama, please follow me."

"Thanks. I appreciate it."

"Not at all—it's my duty." The Kakushi's thoughts raced beneath the mask. 'Dragon Hashira is incredibly strong, yet so kind and humble!'

...

<><><><><><><><>

Hashira Meeting

"You are this generation's strongest Hashira-level swordsmen—Gyomei, Kyojuro, Sanemi, Giyu, Tengen, Muichiro, Obanai, Mitsuri, Shinobu, and Kaidō, who joined us today. I believe it won't be long before Muzan Kibutsuji meets his end at the hands of this generation's warriors." Kagaya's voice carried absolute conviction.

"Master, regarding the Dragon Hashira—what kind of person is he exactly? He's young, but his strength is formidable." When Sanemi asked this question, his tone was logical and measured, completely lacking his usual explosive temper.

"Regarding Ryūjin Kaidō, I've learned his history... His family is exceptionally powerful, and his ancestors once had connections with the Demon Slayer Corps."

Kagaya paused, letting the information settle.

"However, internal conflict tore his family apart. Civil war erupted, and he lost both parents. The family sent assassins to hunt him down. According to our investigation, Muzan Kibutsuji was involved in orchestrating this tragedy."

The Hashira listened in silence.

"Eventually, Kaidō escaped and wandered as a fugitive. By chance, he encountered a merchant vessel and stowed away, which brought him here."

Kagaya's expression grew somber. "Sanemi, the pain and sorrow he's endured isn't something someone his age should have to bear. So if you have time, I hope you'll all reach out to him, talk with him."

"But I didn't sense any hatred toward demons from him," Sanemi said.

"Every human heart contains both light and darkness. When everything is hidden away, the more peaceful things appear on the surface, the more turmoil lies beneath. Even he will have a breaking point someday." Kagaya's tone remained calm.

"I understand." Sanemi's thoughts raced. 'So you're just hiding it all. If those traitors from his family were to die...'

Kagaya seemed to read Sanemi's thoughts. "Sanemi, you must never do that. His family was powerful enough that even Muzan Kibutsuji couldn't oppose them. And they're all gone now."

"What?? Even Muzan couldn't handle them? Then why don't they exist anymore?"

"Greed. Greedy people always pay the price eventually."

"Yes, sir."

The Hashira fell into contemplative silence after hearing Kagaya's explanation.

...

Butterfly Mansion

Following the Kakushi's guidance, Kaidō arrived at the Butterfly Mansion. Aoi Kanzaki came out to greet the visitor, and after hearing the Kakushi explain this was on Shinobu's orders, she led Kaidō to the rear courtyard to rest.

At that moment, Kaidō was reviewing the identity information the system had created for him. The more he read, the more depressed he became, his eye twitching non-stop.

"System, what the hell is this backstory you gave me? Why is it so melodramatic?? Family conflict? Exile and wandering?? And you tied it to that bastard Muzan—that effeminate piece of garbage boss??"

[Ding! If Host is dissatisfied, the system can rearrange the identity. However, everything will reset from the beginning.]

A cross-shaped vein popped on Kaidō's forehead. But after thinking for a moment, he let it go.

He was just a visitor to this world. Once the quests were complete and his Interdimensional Energy hit one hundred percent, he'd leave. Why get worked up over the details?

"Forget it. I'm just passing through anyway. No need to rearrange anything."

[Understood.] The system went silent.

"Let's check the quest rewards."

[Ding! Quest Complete: Defeat Any Three of the Nine Hashira to Prove Your Strength. Progress: 3/3]

[Rewards: Enhanced Mental Reinforcement Serum x1, Custom Demon Slayer Corps Uniform (Enhanced), Interdimensional Energy +7%]

[Current Interdimensional Energy: 30%]

"Another step closer to going home! I'll use the Enhanced Mental Reinforcement Serum tonight." He turned his attention to the Corps uniform—and immediately, two more cross-shaped veins appeared on his forehead.

"System, I have every reason to suspect you're a complete degenerate."

The Corps uniform the system provided was actually pretty stylish—a black-striped white hoodie, long enough to reach his knees given his height. The inner layer was a long-sleeved, high-collared white robe that, according to the system description, was breathable and maintained perfect temperature year-round.

The boots were high-tops that reached halfway up his calves.

All of that was perfectly normal.

What wasn't normal were the pants—denim short-shorts that barely extended past his hips, complete with leather garter straps around the thighs.

The entire exposed-leg aesthetic had a distinctly... questionable vibe to it.

[Ding! Please rest assured, Host—the system is operating normally and absolutely does not have any ulterior motives regarding Host's exposed legs. Please trust this system! (´▽`ʃ♡ƪ)]

Kaidō wanted to rage. Wanted to unleash a torrent of profanity. But after a moment, he resigned himself to helplessness.

After calming down, he decided there was no point arguing. He still needed the system to get home, and it was just clothing anyway. Why make a fuss?

Yeah. Really. No reason to make a fuss.

He found a wooden post, carved the characters [DEMON SLAYER] into it, drew his greatsword, and proceeded to hack it to pieces.

Meanwhile, the [Demon Slayer System] was trembling somewhere in the digital ether, feeling like something was very wrong but unable to pinpoint exactly what. That didn't stop it from continuing to admire Host's appearance, though.

System: [(￣▽￣)~] Whatever's happening, it doesn't interfere with enjoying the view.

"Why do I feel like someone's staring at me...?" Kaidō muttered.

...

That Evening—Butterfly Mansion

"So... do you really have to watch?"

"Oh my, of course I do! I need to examine you properly!"

"But is it really necessary for me to take my shirt off?"

"I'm only asking you to remove your upper clothing so I can check your injuries. It's not a big deal—I'm not making you strip completely naked."

"There's no need. Really. I'm not injured!"

"Oh? You're blushing. What are you afraid of? Just let me take a look."

"...Fine."

Kaidō removed his shirt, allowing Shinobu to conduct her examination.

"You know, you look so small, but your body is surprisingly well-developed. Ufufu~" Shinobu held her stethoscope with barely concealed amusement, clearly enjoying teasing him.

"Don't~" Kaidō's face turned bright red.

"Alright, alright, I'll stop teasing you. Your body is basically fine—no major issues."

She tilted her head, studying his forehead. "But what's this mark? It looks so unusual. Is it a tattoo? And your eyes—why do you have heterochromia like Obanai?"

"It's better if you don't know." The Demon Slayer Mark reduced lifespans to a maximum of twenty-five years. His own mark was system-provided and had no side effects, but if Shinobu learned about marks in general, she'd probably try to unlock one herself—especially since she still wanted revenge for her sister.

Besides, he hadn't activated the mark during his sparring matches with the three Hashira. If he had, the other swordsmen nearby might have resonated with it and awakened their own marks. That could trigger a butterfly effect and drastically alter the timeline—an outcome he absolutely wanted to avoid.

In retrospect, earning their recognition without activating the mark was probably for the best.

As for his eyes—the Phantom Eye was a system reward. Even if he explained, Shinobu probably wouldn't believe him. Better to say nothing.

Shinobu didn't press the issue, though she couldn't shake the feeling that the mark on his forehead was somehow different. She just couldn't articulate how.

"I've had Aoi prepare a room for you. Get some rest." Her smile never wavered—the mask she wore to imitate her late sister, hiding her true self.

"Thank you."

...

Back in his room, Kaidō retrieved the Enhanced Mental Reinforcement Serum from his system inventory. The liquid was deep crimson, like fresh blood.

He opened it and drank without hesitation.

Immediately, intense vertigo slammed into him. His head felt like it weighed a thousand pounds. It was as if his soul had been ripped from his body and was being whipped—agony beyond description, a hundred times worse than the first Mental Reinforcement Serum.

"Ngh!" Since he was in the Butterfly Mansion, Kaidō didn't dare make noise and disturb the others. He bit down hard, enduring in silence. Cold sweat poured down his face, soaking his clothes.

"It hurts... but if this is what it takes to go home, I'll endure anything."

He didn't know how long it lasted. The enhanced serum's effects were too powerful. Eventually, Kaidō couldn't hold on any longer and passed out.

...

The Next Morning

Kaidō woke feeling refreshed despite the ordeal. Remembering last night's suffering, he swore never to go through that again.

But the benefits were undeniable—his mental strength had skyrocketed. His thoughts were clearer, his willpower more resolute.

"What's that smell?" Something reeked. After sniffing around, he realized the source was himself—specifically, the dried sweat coating his body.

"Oh god, I stink! That has to be from sweating buckets during that nightmare last night. How the hell did I not die of dehydration?? I don't know whether to feel lucky or cursed."

He immediately left the room, found Aoi, asked where the bath was, and went to clean himself up.

"That's so much better. Nothing beats a good bath!" He changed into the system-rewarded uniform. Despite his earlier complaints, it was actually pretty comfortable.

"CAW CAW! Dragon Hashira Ryūjin Kaidō! Master summons! Master summons! CAW!" Kuroha swooped down and landed on his shoulder.

"Got it." Kaidō strapped on his greatsword, positioned his fox mask on his head, and headed out with Kuroha.

...

"Morning, everyone!" Kaidō arrived at the courtyard where the Hashira had gathered and greeted them with a smile.

"Good morning, young Kaidō!" Rengoku's voice boomed as enthusiastically as ever.

"Yo! What a flamboyant outfit! Truly worthy of someone as flamboyant as you!" Tengen grinned.

"Tengen-san, you're looking pretty flamboyant yourself today! Forget riches or glory—being you is the only thing worth envying!"

"Hahaha! I love that line!" Tengen burst out laughing.

"Mitsuri-nee, Obanai-san, you both seem to be in good spirits today!"

"Mm." Obanai was always happiest when he was near Mitsuri.

"Oh my! Kaidō-kun, good morning! That outfit is so adorable!" Mitsuri beamed.

"You flatter me, Mitsuri-nee. You look beautiful today!"

'He called me beautiful! Ah~ I'm so happy! I want to hug him so badly!' Mitsuri's internal monologue was working overtime.

After greeting the other Hashira, Kaidō stood beside Giyu, waiting for the Master's arrival.

"The Master has arrived." Hinaki and Kanata spoke in unison.

"Good morning, my beloved children." Supported by the twins, Kagaya approached the assembled Hashira.

All ten Hashira bowed—except Kaidō, who simply bent at the waist. Since Kagaya had explained Kaidō's backstory yesterday, none of the others took offense.

"Seeing the Master in good health brings this subordinate genuine joy," Sanemi said formally.

"Kaidō, did you rest well last night?" Kagaya asked gently.

"Thank you for your concern, Master. Everything was fine."

Kagaya smiled and nodded. Then his expression shifted slightly.

"Kaidō, my child—would you be willing to tell everyone about the mark on your forehead?"

"?!"

<><><><><><><><>

"Kaidō, my child—would you be willing to tell everyone about the mark on your forehead?"

"??"

The Hashira's curiosity was immediately piqued. They'd all assumed Kaidō's dragon-shaped marking was just a tattoo, like Tengen's face paint. But hearing the Master bring it up suggested something far more significant.

Their eyes turned toward Kaidō in unison.

Kaidō wasn't particularly surprised that Kagaya knew—after Shinobu had examined him, she'd reported the unusual mark to the Master. She'd sensed something different about it, something that wasn't quite a tattoo, though she couldn't articulate exactly what.

Kagaya had then asked his wife, Amane Ubuyashiki, to investigate. After a night of research, she'd uncovered records from the Sengoku period describing swordsmen who'd manifested similar marks. Unlocking these marks dramatically amplified the bearer's abilities.

Furthermore, when one person awakened a mark, others nearby would resonate and unlock their own. However, the records contained no information about how to trigger the marks—only one chilling detail: every marked swordsman died before reaching age twenty-five.

Understanding how Kagaya had discovered the mark's existence eased Kaidō's confusion. But it was immediately replaced by hesitation.

He'd hoped to keep this secret indefinitely. His plan had been simple: unlock his own mark, help eliminate all the Upper Ranks and Muzan, then disappear before anyone figured it out.

Then again, maybe this was inevitable. In the original timeline, Tanjiro had been the first to manifest a mark, and after investigation, everyone eventually learned how to trigger them anyway.

Kagaya seemed to sense Kaidō's internal conflict. "If you'd prefer not to share, that's perfectly acceptable. It's your right to keep this private. Whatever you decide, I'll respect your choice."

Kaidō took a breath. "Master, if this information can help everyone, I'll gladly share it. I'm happy to assist however I can. But..." His expression grew serious. "You're aware of the consequences of unlocking the mark, aren't you?"

His own mark was system-granted and carried no penalty. But everyone else? They'd be trading years of life for power.

"Yes. According to the records, every swordsman who unlocked a mark died before reaching twenty-five."

Kagaya's words sent shockwaves through the assembled Hashira. They looked at Kaidō with a complex mixture of sympathy, sorrow, and hope—hope that he might reveal the secret despite his shortened lifespan.

If unlocking marks increased combat strength enough to kill Upper Ranks, most of them would gladly accept a shorter life.

"What's with those looks? Who cares if I live past twenty-five or not? As long as we can kill that bastard Muzan Kibutsuji, it's worth it." Kaidō's voice carried absolute conviction.

"Exactly! If it means destroying Muzan, becoming a short-lived ghost is a small price!" Sanemi's agreement was immediate and fierce.

"Namu Amida Butsu. Indeed—if we can eliminate Muzan, I would have no regrets, even in death." Tears streamed down Gyomei's face as he spoke.

"Alright then. I'll explain how to unlock the mark. Whether you choose to pursue it is up to each of you individually."

Kaidō paused, organizing his thoughts.

"The conditions are extremely harsh. Your body temperature must reach thirty-nine degrees Celsius or higher, and your heart rate must exceed two hundred beats per minute."

"Can humans even survive those conditions?" Shinobu's medical knowledge made her skeptical.

"For ordinary people? Absolutely not. Just hitting thirty-nine degrees would render most people immobile, never mind maintaining a heart rate over two hundred. But for those who've mastered Breathing Styles, it's different. Under these extreme conditions, you can unlock your body's latent potential. The Breathing technique amplifies that potential and manifests as the mark."

"That's it? Doesn't sound too complicated!" Sanemi's confidence was immediate.

"Your simple-minded optimism is almost enviable," Giyu said flatly.

"What did you just say??"

"Nothing."

Kagaya raised a hand for silence, then turned back to Kaidō. "Child, thank you for sharing this knowledge. Your contribution to the Demon Slayer Corps cannot be overstated."

"You're too kind, Master. This is the least I can do. I'm glad I could help."

"Then today's meeting is concluded. I hope we can all gather like this again soon."

...

"Whoa. So this is the estate the Master prepared for me? Pretty impressive!"

After the meeting, Kagaya had arranged accommodations for Kaidō. Every Hashira received their own estate and a designated patrol region. Looking at his new home, Kaidō couldn't help but appreciate the gesture.

The Master really does look after everyone. Even something as simple as housing shows how much he cares about his people.

The estate featured a courtyard with decorative rock formations and a small pond. The house itself had two floors—the first containing a spacious living room and kitchen fully equipped with furniture, the second holding a master bedroom, guest room, and study.

Standing at the master bedroom window, Kaidō could see the Butterfly Mansion in the distance and a mountain stream beyond.

"CAW CAW! Southeast! Southeast! Suspected demon activity! Dragon Hashira Ryūjin Kaidō, investigate! Investigate!" Kuroha swooped down and landed on Kaidō's shoulder, delivering the mission briefing.

[Ding! New Quest Available.]

[Quest 1: Investigate the Cause of Missing Persons.]

[Rewards: Hyper-Awareness, Random Interdimensional Energy 1-5%]

[Quest 2: Eliminate Lower Rank Three—Wakuraba.]

[Rewards: Dragon Breathing Final Form, Enhanced Longevity Pills x12, Random Interdimensional Energy 5-15%]

[Hyper-Awareness: Allows you to sense all movement within your vicinity, enabling faster reaction times in combat.]

[Dragon Breathing, Tenth Form: Ultimate Art—Judgment Slash: Lock onto your target and unleash ten consecutive strikes at lightning speed with unpredictable trajectories. Power scales with user strength.]

[Enhanced Longevity Pills: System-modified pills that extend lifespan, eliminate negative side effects, and significantly reduce even curses.]

"A quest already? So there's a Lower Rank in my patrol zone?"

Kaidō didn't know much about the Lower Ranks. Aside from Enmu, most of them had been immediately executed by Muzan shortly after their introduction in the story. Information about their Blood Demon Arts was virtually nonexistent.

"Got it. I'm on my way."

His patrol zone, his responsibility. Time to investigate.

He grabbed his fox mask, strapped on his greatsword, and departed immediately.

...

Arriving at the town, Kaidō found a small tea shop to gather information. To avoid drawing unnecessary attention, he stored his greatsword in his system inventory—walking around with a sword that size strapped to his back was a bit too conspicuous.

He found a seat and called out, "Boss, pot of tea please."

"Coming right up, miss!"

A vein popped on Kaidō's forehead. "Boss. I'm a guy."

"My apologies! I'm so sorry!" The owner bowed repeatedly.

...

A few moments later, the owner returned with tea and sweets. "Here's your tea, sir! The sweets are complimentary—my apology for the earlier mistake. You look unfamiliar though—first time in Higashino Town?"

The owner studied Kaidō's unusual outfit, clearly assuming he was some wealthy young master.

"Yeah, first time. I'm a traveling novelist—I collect strange and unusual stories for my writing. You wouldn't happen to know any interesting local tales? I'm looking for inspiration."

"A novelist! That explains the unique fashion sense—never seen anything quite like it!"

The owner leaned in conspiratorially. "Now that you mention it, there is something strange happening lately. People have been disappearing from town without a trace. The only clues left behind are piles of withered leaves and bloodstains."

He glanced around nervously before continuing. "It only happens at night. Everyone locks their doors and windows once the sun goes down—nobody dares go out after dark. Creepy, right? And listen—"

He moved even closer, voice dropping to a whisper. "Some folks are saying it's demons. That the missing people were eaten by demons. So, uh, maybe don't go wandering around after sunset, if you know what's good for you."

"That is pretty interesting! Perfect material. Anyway, I've been traveling all day—I should find an inn and rest up. Here's for the tea and sweets. They were excellent, by the way." Kaidō paid and stood to leave.

"Come back anytime!"

<><><><><><><><>

Nightfall

Demons only operated after dark, so Kaidō had spent the day resting at an inn, conserving his energy for the coming fight.

"Everything's ready. Time to find out which unlucky bastard is causing trouble." He slipped out the window under cover of darkness and headed toward the disappearance sites.

The tea shop owner had mentioned a small forest just outside town. Kaidō entered the tree line and began searching for clues.

After an extensive search turned up nothing useful, he was about to give up when a strange smell caught his attention.

"What's that odor?" He sniffed the air. "Weird... smells like rot mixed with something else. Wait—"

His instincts screamed a warning. He leapt backward just as several leaf-shaped projectiles—like shuriken—embedded themselves where he'd been standing. They looked coated with poison.

"Well, well! Someone actually dodged that. You've got quick reflexes!" A figure emerged from the shadows.

Moonlight illuminated his features—three X-shaped marks on his cheeks and forehead, pointed ears with earrings, and the kanji for Lower Three carved into his left eye.

"Twelve Kizuki, Lower Rank Three—Wakuraba."

"Oh? Someone actually recognizes me! Judging by your appearance, you're with the Demon Slayer Corps, right? But you can't be anyone important. As long as you're not a Hashira, you'll make a fine meal! Demon Slayers taste delicious, you know. Hahahaha!"

Wakuraba's eyes gleamed with murderous intent. "Once I eat you, I'll become even stronger."

"Has anyone ever told you that you talk too much?"

Kaidō lowered his fox mask over his face and, right in front of Wakuraba, pulled his greatsword from thin air via the system inventory.

Wakuraba's eyes widened. 'Did he just pull that sword from nowhere? Is he a demon too? No—he doesn't smell like one. He doesn't have that person's scent.'

"I don't care what trick that was. As long as you're not a Hashira, you don't scare me!"

"Blood Demon Art: Decaying Leaves!"

Withered leaves materialized around Kaidō, accompanied by an overwhelming stench of rot. Anything the leaves touched began to blacken and decay.

While Kaidō was distracted by the swirling leaves, Wakuraba closed the distance in an instant, throwing a punch aimed directly at his skull.

"Dragon Breathing, First Form: Dragon's Breath."

CLANG!

Kaidō's greatsword intercepted Wakuraba's fist with a metallic crash. He immediately pushed the demon back, creating distance.

"I see. So your Blood Demon Art creates poisoned leaves that infect people on contact. If I'm right, they also have a paralytic effect. That's what happened to the missing people—they touched the leaves, got paralyzed, couldn't scream for help. By the time anyone found them, all that remained was leaves and blood."

[Ding! Quest Complete.]

[Quest 1: Investigate the Cause of Missing Persons.]

[Rewards: Hyper-Awareness, Interdimensional Energy +3%]

[Current Interdimensional Energy: 33%]

[Hyper-Awareness fusion initiated... Fusion complete!]

The system notification chimed in his mind. One quest down, one to go. The Hyper-Awareness ability integrated instantly, sharpening his perception to supernatural levels. Every shift in the air, every tremor in the ground—nothing would escape his notice now.

"Heh. So you figured it out. Doesn't matter—you're still going to die. I'm one of the Twelve Kizuki!"

"Blood Demon Art: Maple Shower!"

A barrage of maple leaves shot toward Kaidō like razor-sharp throwing stars, piercing through everything in their path.

"Dragon Breathing, Fourth Form: Coiling Dragon."

Kaidō planted his greatsword in the ground. A translucent barrier formed around him, deflecting the leaf storm.

Then: "Dragon Breathing, Ninth Form: Cyclone Pierce!"

Blade and body spiraled forward in a high-speed drilling motion, boring straight toward Wakuraba.

"Shit! Blood Demon Art: Wither!"

Wakuraba unleashed a technique that caused all surrounding plant life to decay and die, hoping to drain Kaidō's vitality and immobilize him.

But Cyclone Pierce—enhanced by Dragon's Breath—was too fast and too powerful. The spinning assault punched clean through Wakuraba's torso, emerging from the other side.

"AHHH!" The demon screamed, looking down in shock at the massive hole in his chest. Even his regeneration had slowed dramatically.

"Damn you, Demon Slayer! Damn you! Blood Demon Art: Stealth!"

Wakuraba's form vanished as if he'd never existed.

'Shuriken-style attacks and stealth techniques... He was probably a shinobi before becoming a demon. Like Tengen.' Kaidō didn't lower his guard, gripping his sword tightly.

Using his newly acquired Hyper-Awareness, he extended his senses outward, reading every disturbance in the environment.

"Found you."

Wait—something's off. No heartbeat. Even demons have heartbeats. This must be a decoy!

"Hehehe... keep searching, you bastard. Once you let your guard down, I'll strike. Then I'll torture you slowly while you watch me eat you piece by piece!" Wakuraba's thoughts were venomous.

"There you are! Hiding in the tree!"

When Wakuraba had activated Stealth, he'd simultaneously created a Body Double and concealed his true self in the branches above, waiting to ambush Kaidō.

"Huh? Where'd he go? When did he disappear??" Panic set in. Kaidō had vanished in an instant. A primal sense of danger made Wakuraba scan his surroundings frantically.

"Dragon Breathing, Second Form: Dragon Claw!"

Kaidō's form materialized above the tree, blade descending in a devastating vertical slash.

"When did you—"

SCHLICK.

Wakuraba's body split in half. As he fell from the tree, a blood collection device embedded itself in his flesh—Kaidō had tossed it mid-strike.

He'd forgotten to collect Kamanue's blood last time. No way was he making that mistake again—he'd promised Tamayo.

Kaidō walked over to the bisected demon and extracted the collection device. "Hide-and-seek's over."

"You bastard... why won't I heal?? HEAL, DAMN IT! What did you do to me, you cursed Demon Slayer??" Wakuraba's severed halves writhed on the ground, screaming in impotent rage.

"You're noisy. Dragon Breathing, Fifth Form: Violent Tempest!"

A hundred blade projections shredded Wakuraba into paste. Kaidō didn't stop until the demon was nothing but scattered ash.

[Ding! Quest Complete.]

[Quest 2: Eliminate Lower Rank Three—Wakuraba.]

[Rewards: Dragon Breathing Final Form, Enhanced Longevity Pills x12, Interdimensional Energy +7%]

[Current Interdimensional Energy: 40%]

"The Final Form... with this, I can hold my own against even Upper Ranks. But I can't slack on training—mastering these techniques is still on me."

"And the Longevity Pills! These can counteract the mark's side effects. They should work on Master Ubuyashiki's curse too—can't eliminate it completely, but at least delay the progression."

His thoughts turned to the energy total. "But what I really care about? Forty percent Interdimensional Energy. I'm almost halfway home!"

"Meow~"

A cat appeared—Chachamaru, Yushiro's demon feline. Kaidō placed the blood collection device in the box on the cat's back and scratched behind its ears. "Thanks for the help, Chachamaru."

The cat purred, enjoyed the attention for a moment, then vanished with a soft "meow."

"Mission complete. Time to head back to the inn. Kuroha, where did you— Oh, right. That bird definitely flew straight to Headquarters to broadcast the news. Again."

Kaidō sighed in resignation. Whatever. Not a big deal.

"Since I'm already out here, might as well enjoy my patrol zone for a while. Clear out some low-level demons, get some practice in. Hehehehe! Wonder which poor bastard demon I'll run into next?"

Something dark and mildly sadistic had awakened in Kaidō's personality.

He returned to the inn, leaving the cleanup to the Kakushi.

...

The Next Day—Demon Slayer Corps Headquarters

"CAW CAW! Dragon Hashira Ryūjin Kaidō has slain Lower Rank Three! Dragon Hashira eliminated Lower Rank Three! CAW CAW!" Kuroha circled Headquarters, broadcasting at maximum volume.

"Mm! Young Kaidō defeated another Lower Rank! Splendid!" Rengoku's approval boomed across the training grounds.

Tengen, currently soaking in a hot spring with his three wives, grinned. "What a flamboyant guy! Another Lower Rank down. That's two this month. Truly flamboyant!"

Gyomei paused his training. "Namu Amida Butsu. Kaidō, you continue to grow stronger." Tears streamed down his face as he resumed his meditation.

"Tch. Just a Lower Rank. I won't lose to you!" Sanemi grabbed his sword and stormed toward his patrol zone.

Ubuyashiki Estate

Hearing Kuroha's announcement, Kagaya smiled. "My beloved child grows stronger still. How wonderful. One day, he'll surpass us all."

...

...

...

One Month Later—Just Before Dawn

SLAP! SLAP! SLAP!

"Talk! Come on, say something!"

"I'm asking you a question! Answer me! Are you going to talk or not??"

SLAP!

"SPEAK! I'm waiting! WILL YOU TALK OR NOT??"

"TALK ABOUT WHAT?? YOU HAVEN'T EVEN ASKED ME ANYTHING! HOW AM I SUPPOSED TO KNOW WHAT TO SAY?? You're not even human—what kind of Demon Slayer tortures demons like this?? SOB... Being a demon is hard enough without you!"

A demon tied to a tree was crying hysterically, utterly miserable.

He'd just been trying to find food. Spotted a lone child walking home and was about to grab a meal when this lunatic appeared out of nowhere, dragged him into the forest, and knocked him unconscious.

When he woke up, he was bound to a tree getting repeatedly slapped across the face. When the slapping got boring, his captor switched to a stick. And the whole time, he kept demanding answers without asking any questions.

"Oh, right. What was I going to ask again? Eh, forget it. You made me lose my train of thought anyway. I'll just beat you up instead!" Kaidō resumed the face-slapping with renewed enthusiasm. When his hand got tired, he grabbed a branch.

"Sob sob sob... this is so humiliating..."

Dawn broke.

Sunlight—a demon's natural enemy—began creeping across the forest floor. The bound demon saw it like a beacon of salvation. Summoning his last reserves of strength, he snapped the ropes and threw himself into the light.

"I'M FREE! Do you know what I've been through for the past five hours?? FIVE HOURS! You're inhuman! I just wanted a snack! I'd rather starve! I'd rather burn in the sun than endure another second of your torture!"

The demon stood in direct sunlight, letting it consume him. His final expression was one of relief.

Kaidō's eye twitched. "Why does that line remind me of those old Blue Moon commercials?"

The [Demon Slayer System], which had been watching all night, felt compelled to ask: [Host, are you... okay?]

"I'm fine! I was just practicing my interrogation techniques. How was I supposed to know these demons would be so fragile?"

[That wasn't interrogation. That was psychological warfare. A human would've had a mental breakdown.]

"Huh. Good point. Whatever—I've been out here a month already. Time to head back to Headquarters. Kuroha, let's go! Back to the inn. We're leaving tomorrow."

Kuroha, perched on a branch, glided down to Kaidō's shoulder.

Over the past month, the crow had watched his master capture demon after demon. Twenty-three in total. At first, Kuroha thought Kaidō was interrogating them about Muzan's location.

Turns out, nope. Just "practice."

He'd tied them to trees in increasingly creative positions—upright, suspended, inverted, you name it. Every captured demon spent an entire night getting "practiced on" before either begging for a merciful death or, like today's victim, choosing suicide by sunlight.

Kuroha had long since stopped being surprised. He'd accepted his fate. As long as his master fed him well and gave him head scratches, life was good.

...

"Mmm, that was a good sleep!" Kaidō stretched and glanced out the window. "Wait, did I sleep a whole day? Whatever. Grab some food, then travel through the night back to Headquarters."

He checked out, bought rice balls from a street vendor, and set off.

Walking down a quiet path, he spotted a demon skulking in the shadows, acting extremely paranoid.

Kaidō's face split into an innocent, angelic smile. "Well, well... another practice dummy. This'll be fun. Hehehe!"

The system watched that smile and thought: [Another poor soul about to experience hell.]

Kuroha simply perched on a tree branch, resigned to spectating.

The demon felt a chill run down his spine, like someone was staring at him.

He'd heard stories this past month—stories about a terrifying Demon Slayer who captured demons and tortured them beyond death. Supposedly a Hashira. He hadn't believed it at first, until he saw one of his fellow demons get caught and literally beg to die.

After that, he'd hidden. But tonight, hunger had finally driven him out. Surely that hunter was gone by now, right?

The feeling of being watched intensified. He slowly turned around. Nothing there.

"Phew. Just my imagination. I'm too paranoid. Gotta find food and hide again."

When he turned back around, there was someone standing directly in front of him.

At first, he thought it was just a human. Then he recognized the hunter.

His legs gave out. He collapsed, screaming: "DEMON! MOMMY, HELP ME!"

...

Later, tied upside-down to a tree: "Please, I'm begging you! Let me go! I'll never hurt humans again! I'll never eat people! Please, have mercy—I'm old! AHHHHH!"