"Woah."
Zenitsu's mouth hung open as he stared at the brightly lit street before them. Even in daylight, the entertainment district was dazzling, with colorful banners and decorations adorning every building. The vibrant reds and golds caught the afternoon sun, creating a spectacle that seemed almost dreamlike.
"So many colors! Is this what they call fancy?!" Inosuke shouted, already darting forward with his characteristic lack of restraint, weaving between pedestrians who jumped out of his way.
"Don't run around and get lost!" Uzui's large hand shot out, grabbing both Inosuke by the collar and Zenitsu by the shoulder before either could wander too far. "We're not here to sight see. Stay close and try not to draw attention."
The group walked deeper into the city slowly, partly to conceal their special identity as Demon Slayers—the last thing they needed was to announce their presence. And partly because some of them were genuinely tired from the long journey. Tanjirou walked constantly scanning their surroundings with that observant nature of his, while Zenitsu dragged his feet with exaggerated exhaustion.
Mitsuru observed them all with barely concealed amusement, a slight smile playing at the corner of his lips.
These guys are truly a handful. It's a shame I won't get to see them in their female disguises later—that would be enough entertainment to last me a year. Though I suppose Uzui-san wouldn't appreciate me sticking around for that particular show. His smirk widened slightly. When did I become this mischievous? Is this because I regressed? I guess my feelings are more heightened.
"Everyone, I'll stop here," Mitsuru announced, gesturing toward the modest inn across the street."If you need anything, I'll be at that inn over there. You're welcome to come find me whenever."
"You sure you don't want to stick with us?" Tanjirou asked.
"I appreciate the offer, Tanjirou, but I'll be fine on my own," Mitsuru assured him with a casual wave. "Besides, Uzui-san has enough to worry about without adding another person to his roster. I'll be around if you need anything."
Uzui nodded curtly, though his eyes studied Mitsuru for a moment longer. "Don't do anything reckless."
"Wouldn't dream of it," Mitsuru replied with that familiar gleam in his eyes.
With final nods exchanged, Mitsuru bid farewell to the four and made his way to the inn.
---
Meanwhile, the quartet made their way to Uzui's designated meeting place—a private room in a more discreet establishment. Once inside with the door closed, Uzui's expression turned serious.
"Alright, before we discuss the main mission, there's something we need to talk about," Uzui began, leaning against the wall with his arms crossed.
"Is it about finding your wives?" Tanjirou asked immediately, his voice filled with concern.
"We'll get to that. First—that Mitsuru is not simple."
The statement left the three youngsters bewildered, exchanging confused glances.
"Hah? That guy?" Inosuke tilted his head, his boar mask shifting. "Of course he's strong! I could tell from just looking at him!"
"He shouldn't be a Demon Slayer, right?" Tanjirou asked, confused. "He doesn't have a Nichirin Blade. And he didn't seem to know about the Corps..."
"Precisely because he's not a demon slayer that I'm saying he's not simple." Uzui leaned forward, his expression grave. "Throughout the entire time with us, he was maintaining Total Concentration Constant."
There was a moment of silence.
"Total Concentration... Constant?" Zenitsu's eyes widened dramatically. "But that's—that's something even most Demon Slayers struggle with!"
"Exactly," Uzui nodded. "Most slayers take months, even years to master maintaining it at all times. Some never manage it at all. Yet this civilian maintains it like breathing—completely naturally, without any apparent effort."
"I did notice his breathing was very controlled," Tanjirou said thoughtfully, his hand moving to his chin.
"It's more than that. His movements, his awareness of his surroundings, the way his eyes tracked everything—he's had real combat experience." Uzui's tone was serious. "Those aren't the habits of someone who's done some casual training. That's someone who's fought for their life and survived."
"How can you tell all that just from walking with him?" Zenitsu asked nervously.
"Experience. When you've been a shinobi as long as I have, you learn to read people." Uzui uncrossed his arms. "Plus his sword handling. Did you notice how he carries his blade? The wear on the hilt, the way his hand naturally rests on it? That's not decorative—he uses it regularly."
"Well, I didn't sense any ill intent from him," Tanjirou said, his voice confident. "His scent was... complicated, but not malicious. But there was this huge fighting intent from him, even though he held it back."
"Yeah! That's exactly why I wanted to fight him!" Inosuke interjected enthusiastically, bouncing on his heels. "I could tell he was strong! The Lord of the Mountain demands a battle!"
"Is that... bad?" Tanjirou asked hesitantly, worry creeping into his voice. "Should we be concerned?"
"Not necessarily. Battle maniacs can be incredibly useful allies—they don't run when things get dangerous, and they often perform their best under pressure. But they can also be unpredictable, reckless even." Uzui stroked his chin. "The question is whether that recklessness will help or hinder."
"So what do we do about him?" Zenitsu asked, wringing his hands nervously.
"For now? Nothing. We keep an eye on him, see what he does. If he's just a skilled civilian who happens to be in the wrong place at the wrong time, we make sure he doesn't get caught up in demon business." Uzui's expression hardened. "But if things go well here, if he proves himself reliable... I'm thinking of introducing him to the Corps properly. Someone with his skill and that level of natural talent shouldn't be wasted."
"You think he'd join?" Tanjirou asked.
"If he's as much of a fight-seeker as I think he is? Once he learns what we do, he'll be interested." Uzui smirked slightly. "The question is whether he can handle it."
"So we might see him fight?" Inosuke perked up even more, practically vibrating with excitement. "Can I fight him?"
"Maybe, if the situation calls for it. But that's not our priority." Uzui's expression turned deadly serious, the playful atmosphere evaporating instantly. "Right now, we have a much more pressing issue. The most crucial problem is the presence of demons in the Entertainment District—and I've lost contact with my three wives."
"They're not just my wives—they're kunoichi, female ninja trained since childhood," Uzui explained, ignoring Zenitsu's outburst in the background. "I sent them here weeks ago to infiltrate the district and gather intelligence on the demons operating in the area. They were supposed to report back regularly, but all three have gone silent."
"That's... that's really bad, isn't it?" Tanjirou's expression grew worried.
"It means either they're deep undercover and can't risk contact, or something's happened to them." Uzui's jaw clenched. "Given the presence of demons here, I'm not taking chances. That's where you three come in."
What followed was a detailed discussion about the mission. Uzui explained the layout of the district, the various establishments, and his plan to have the three youngsters disguise themselves as women and infiltrate the geisha houses where his wives had been placed.
Zenitsu fainted twice during the explanation. Inosuke seemed overly excited about going undercover. And Tanjirou simply accepted his role, though he seemed more concerned about finding Uzui's wives than anything else.
---
Several days passed in the Entertainment District. The boys had been successfully placed in their respective houses, and the investigation was underway.
Mitsuru sat cross-legged on the floor, his back straight and breathing falling into the deep rhythm of Total Concentration.
Alright, let's think this through properly.
This was different from the underground fights or his spars with Saeko. Those had their dangerous moments, sure—Saeko didn't pull her punches, and the underground scene was brutal in its own right. But this? This will be completely different. Creatures that could regenerate from almost any wound, that possessed inhuman strength and speed, that fed on people. One moment of lost focus during battle could mean his death. Or worse, someone else's death because he wasn't fast enough.
Truth be told, I don't even need to enter this battle. His fingers drummed lightly against his blade's sheath, a nervous habit he'd never quite broken. No one's going to die in this arc—not on the heroes' side, anyway. I could just wait it out, observe from a distance, maybe step in only when Uzui fights the Upper Ranks. Learn what I can from watching. That would be the smart play. The safe play.
He exhaled slowly, a rueful smile crossing his face.
But when have I ever taken the safe play?
The truth was simple, almost embarrassingly so: he wanted to fight. That familiar itch was already building under his skin, that electric anticipation of facing something truly dangerous. It was the same feeling he'd chased in his previous life, the same rush that made him feel genuinely alive. He'd tried to suppress it, tried to be more careful now that he had Akane depending on him. She'd probably smack him upside the head if she knew he was actively seeking out deadly combat.
I know I should be more cautious now, he admitted to himself, his expression growing more serious. Akane needs her idiot brother to come home in one piece. But old habits don't just disappear overnight, do they? I've always been a little battle-crazed. Maybe more than a little.
Sorry, Akane. Your brother's an idiot who can't help himself.
He shook his head, refocusing. There was no point in dwelling on what-ifs. He was here, and he was going to fight. That was decided. What he needed now was to prepare properly, to make sure that when the time came, he'd be ready.
Let's see... what do I actually remember about this arc?
He closed his eyes, mentally reviewing the Entertainment District arc as he remembered it. Uzui's three wives had infiltrated various establishments in the district, posing as courtesans and attendants to gather intelligence on demon activity. But they'd lost contact—that was the whole reason Uzui had brought backup. The boys would be disguised as girls and sent into the houses to investigate.
The demon running this district is an Upper Rank, he recalled, his expression growing sharper. Upper Rank Six—Gyutaro and Daki. Two demons sharing one rank, which is already unusual. Daki operates openly, using her position as an oiran. But the real threat is Gyutaro, her older brother. He's the one with the real power.
The mechanics of the fight came back to him in pieces. Daki's Blood Demon Art involved those cloth sashes—razor-sharp, incredibly flexible, and numerous. She could extend them to great lengths, store people inside them, and even detach them to act independently. A nightmare to fight against, especially in an urban environment with civilians around.
And Gyutaro... his Blood Demon Art is poison, isn't it? Incredibly lethal poison. Even a scratch could be fatal. Plus those sickle-like weapons he uses.
The key detail that made this fight so dangerous was that both demons needed to be beheaded simultaneously. Kill one while the other lived, and the dead one would just regenerate. It required perfect coordination, multiple fighters working in tandem.
Tanjirou, Zenitsu, Inosuke, and Uzui will all fight them. Uzui loses his hand and eye in the process, and comes close to dying from the poison. But they win. Everyone survives.
He opened his eyes, staring at the ceiling.
So the question is: where do I fit into all this? Do I help with Daki? Take on Gyutaro? Try to prevent Uzui's injuries?
A thrill of excitement ran through him despite himself. An Upper Rank demon. He'd be testing himself against something truly formidable. The underground fighters, even Saeko at her best—they were nothing compared to centuries-old demons who'd slaughtered countless demon slayers.
Calm down, he told himself firmly, taking a deliberate breath. This isn't about the thrill. Well, it's not only about the thrill. I need to be smart about this. One wrong move and someone could die— maybe even me. And then what would Akane do?
But even as he tried to rationalize it, that battle-hungry part of him was already planning, already imagining the clash of blades, the dance of combat against an inhuman opponent. His fingers twitched against his sword hilt.
Focus, Mitsuru. You've got a few days to prepare. The timeline... Tanjirou and the others infiltrate the houses, gather information, things escalate, and then the demons reveal themselves. That's when everything goes to hell.
He needed to use this time wisely. His Total Concentration Breathing was solid—he could maintain it constantly now, then there was repetitive action and his current trump card selfless state —although he could only manage it for % minutes.
But against an Upper Rank demon, would it be enough?
I should probably practice a bit more, get a feel for moving through this district at night. Learn the layout, the rooftops, the escape routes. If I'm going to do this, I'm going to do it right.
---
The days continued to pass. Mitsuru maintained his routine—familiarizing himself with the terrain during the day, practicing his mobility and techniques at night when fewer people were around to see. He kept his distance from where the boys were working, not wanting to complicate their mission or draw unnecessary attention.
But he stayed alert, his senses always extended, waiting for that moment when things would inevitably go wrong.
On the night of the confrontation, Mitsuru was at his window, having just returned from another practice session on the rooftops. He was about to begin his nightly meditation when he felt it—a faint vibration running through the building's structure.
His body went still instantly, all his senses focusing.
There. Something slicing through wood and stone, moving with unnatural speed. Sashes, piercing through the wooden houses like paper, accompanied by the crack of breaking ground and flying debris.
That's combat. That's a demon attack.
Without hesitation, he grabbed his blade. The window opened and he was through it, leaping to the adjacent rooftop. His body moved with fluid grace, Total Concentration Breathing enhancing his capabilities.
"It's a bit far, but I should make it in time."
His footsteps were light but swift across the rooftops. His heart pounded—not from exertion.
This is it.
A grin spread across his face despite everything. This was who he was—a battle maniac charging toward danger. Akane was right to call him an idiot.
---
At the scene of the battle, Tanjirou faced Daki, but she was clearly toying with him. Her sashes—sharp as blades and tough as steel—attacked from multiple angles like serpents. Each moved independently, creating a deadly web around him.
Despite his injuries, Tanjirou fought back. The water flow that usually surrounded his blade was gone, replaced by explosive flames.
"Hinokami Kagura – Burning Bones, Summer Sun!"
His blade traced a fiery arc, severing the incoming sashes. But Daki only laughed.
"Oh my, how interesting! But can you keep that up?"
Dozens more sashes shot forward from impossible angles. Tanjirou's blade moved so fast it created visible flames through air friction. His strikes were precise, perfectly timed. Not a single sash touched him.
Daki's smile faded. Her hands trembled.
"Impossible," she hissed. "Am I... _afraid_? Of this ugly freak?!"
Blood seeped into Tanjirou's eyes from a forehead cut, but he didn't notice. His focus was absolute—nothing existed except the demon who killed for pleasure.
Daki leaped backward to a rooftop. Tanjirou was already there. A horizontal slash—clean, perfect, deadly.
Sashes flooded the space like a desperate wall. Useless. His blade deflected every single one, opening a path through. He charged forward, blade arcing toward her neck.
_Whoosh._
The blade connected but didn't cut. Daki's neck had transformed into a sash at the last instant, becoming soft and resilient—like cutting rubber with a knife.
"You little—!"
Furious, Daki unleashed a storm of sashes from every direction. But Tanjirou was faster. He stomped down on multiple sashes, pinning them to the rooftop, then severed them all in one cut. Another path opened.
His flaming blade reached her neck again. Her pupils dilated in genuine fear.
This was it—
But Tanjirou couldn't advance another inch. His body had reached its absolute limit. The burst of power died. His muscles screamed, his lungs burned, his vision swam.
The blade trembled and stopped, mere centimeters from her neck.
Tanjirou collapsed forward onto his hands and knees, gasping and retching. The battle had seemed endless but lasted only seconds.
"Humans are truly pitiful."
Daki looked down at him with pity and contempt. Sashes began forming again, ready to kill him.
"Always pushing beyond your limits, only to fall short at the crucial moment. How sad. How utterly—"
"I don't think humans are pitiful at all."
A clear voice cut through the night from a nearby rooftop, stopping Daki mid-sentence.
Mitsuru stood there, silhouetted against the night sky. He'd arrived just in time to witness the end of the exchange.
This was the first demon he had encountered since coming to this world.
And despite the danger, despite the rational part of his mind screaming warnings about Upper Rank demons and poison and the very real possibility of death, despite thinking about Akane and his promise to come home safe—
He couldn't suppress the grin spreading across his face.
Finally.