Breathing Style: Constant and Training

In the afternoon, the Butterfly Mansion enjoyed a rare moment of peace, the scent of medicinal herbs mingling with the smell of sunshine. Moyu sat down on the veranda at a corner of the courtyard and watched Tanjiro meticulously practice basic sword swings nearby, sweat soaking his forehead.

Shinobu Kocho carried over a tea set and sat down silently beside him, her movements as light as those of a real butterfly.

"Tanjiro certainly works hard," she said with a smile, pouring two cups of tea and offering one to Moyu. "But that alone isn't enough."

Moyu accepted the cup and looked at her with his azure eyes.

Shinobu took a sip of tea and said casually, "Come to think of it, Tanjiro and the others don't seem to have mastered Breathing Style Total Concentration: Constant yet. Moyu, did you learn Constant from Mr. Urokodaki on Mount Sagiri? Why don't Tanjiro and the others know it?"

Moyu paused, then admitted, "I don't know it either."

"Huh?" Clear surprise flashed through Shinobu's purple eyes, and even her smile faded a little. "You don't know Breathing Style: Constant? Then how did you defeat Lower Rank Five? Without Constant, it's hard to sustain intense combat and explosive bursts of power."

Moyu raised a finger and pointed to his eyes, those azure eyes that seemed to hold a starry sky.

Shinobu froze for a moment, then realization dawned. "Oh... I see. Is it a special ability from those 'special eyes' of yours?"

"What an enviable talent." It was impossible to tell whether Shinobu's tone held admiration or something else, but she promptly changed the subject. "Still, Breathing Style: Constant is a very important foundation. Even with your special ability, mastering Constant could take your strength to another level. And—"

Her gaze turned to the three boys sweating profusely in the courtyard. "Tanjiro and the others need to learn it as soon as possible. The missions ahead will only get more dangerous."

Moyu fell silent for a moment. Before he transmigrated, he had of course known about Breathing Style Total Concentration: Constant, and even knew it was the key to a Demon Slayer Corps swordsman making a leap in strength. But as for the exact principles and training methods... he hadn't paid much attention to the details when watching the anime, focusing instead on the plot. After transmigrating, he had been busy adapting to this world, training and fighting, and then, with one thing and another, he had completely forgotten to ask Master Urokodaki about Constant.

"Miss Shinobu, could you tell me about Breathing Style: Constant?" Moyu asked.

Shinobu put down her teacup and said seriously, "Simply put, it means making Total Concentration Breathing an instinctive bodily function, maintaining a high-intensity breathing state twenty-four hours a day, even while asleep."

"It isn't just a change in breathing technique, but a fundamental strengthening of the body," she continued. "By continuously breathing in the most efficient way and maximizing oxygen intake, the heart and lungs are trained to their utmost. The blood's oxygen-carrying capacity rises dramatically, and metabolic efficiency approaches the human limit. Even when the muscles aren't active, they continue to receive ample nutrients, becoming stronger and tougher. Even recovery from injuries speeds up considerably."

Moyu listened quietly, his Six Eyes unconsciously working at high speed to analyze the information in Shinobu's words. I see... This isn't just a breathing technique, but a systematic training method that improves the body's overall condition at the cellular level.

"To master Constant, you need to undergo a series of rigorous exercises," Shinobu went on. "First comes basic flexibility and coordination training, then reaction speed and pushing past your physical limits... Only after that do you turn breathing into an instinct. Speaking of which—"

She looked at Moyu, her smile returning. "Since you don't know it either, why not learn alongside Tanjiro and the others? I can teach you."

Moyu considered it, then nodded. "All right."

The next day, training officially began.

First up was flexibility training. The Butterfly Mansion's young attendants brought out an assortment of strange equipment: movable joint-stretching frames, resistance bands and pulley systems for stretching muscles, and obstacle devices that required the trainees to twist their bodies to get through.

"What are we doing?!" Zenitsu had a bad feeling as he looked at the equipment.

Aoi explained sternly, "This is to improve your flexibility and coordination. Especially you three. Your injuries haven't fully healed, so you need stretching even more to help you recover."

Tanjiro obediently stepped forward first. The attendants Kiyo Terauchi, Sumi Nakahara and Naho Takada—the three cute girls with distinctive dot eyes—began helping him stretch.

"Aaaah—!" Tanjiro's screams instantly rang throughout the Butterfly Mansion. His body was bent and stretched at all sorts of incredible angles, his joints giving faint cracking sounds.

"It hurts! It hurts! My bones are going to break!" Tears spurted from Tanjiro's eyes.

"Bear with it, Kamado! This is for your own good!" Aoi said sternly, her hands showing no mercy.

When it was Inosuke's turn, the boy from the mountains put on a brave front at first. "Hmph! Gontaro's so useless, making a fuss over something this little! I'm—aaaah, it hurts, it hurts!! My bones are gonna break!! Let go! What are you ugly women doing to me!!"

Inosuke's screams were even more dramatic than Tanjiro's. He struggled like a fish thrown onto land, but Aoi and the dot-eyed trio held him firmly down.

Moyu stood to one side and watched without taking part. Thanks to the natural changes wrought by his Sage Body, his flexibility and physique had long since surpassed the level ordinary people needed to train to reach. This was essentially part of rehabilitation, and since he wasn't injured, he naturally didn't need it.

Last was Zenitsu.

"Zenitsu, it's your turn." Aoi looked at him.

Zenitsu looked at the equipment, and his eyes suddenly lit up: the people assigned to stretch him were several of the Butterfly Mansion's young female attendants, including Aoi herself.

"Ah~ beautiful ladies~ please be gentle~" Zenitsu immediately put on a dreamy expression and willingly lay down on the mat.

When the girls began stretching him—

"Oh~ right there~ a little harder~ ah~ that feels good~" Zenitsu made strange noises, his face full of bliss, as though he weren't undergoing painful stretches but receiving a top-class massage.

Tanjiro and Inosuke were grimacing in pain. Seeing Zenitsu like that made them feel even more aggrieved.

"Why's this guy enjoying himself so much?!" Inosuke roared.

"Zenitsu... doesn't it hurt?" Tanjiro asked weakly.

"Hurt? How could it hurt? With so many cute ladies helping me personally, this is heaven, heaven~" Zenitsu closed his eyes, looking blissful.

Moyu: "..."

He looked away, feeling that his eyes would suffer if he kept watching.

After flexibility training came reaction training.

A low table stood in the center of the training area, with two teacups full of dark brown medicinal brew on it. Shinobu Kocho and Kanao Tsuyuri stood beside the table.

"The rules are simple," Shinobu said with a smile. "Two people sit facing each other, with their hands on their knees. When I say 'begin,' you must quickly pick up a teacup and splash the medicine on your opponent. But—"

She paused, her smile deepening. "If your opponent pins down your cup or your hand before your fingers touch the cup, you can't move anymore. Whoever splashes the other person first, or stops them from moving, wins."

"First, Tanjiro against Kanao Tsuyuri."

Tanjiro and Kanao Tsuyuri sat facing each other. Tanjiro was completely focused, while Kanao Tsuyuri remained expressionless, her pink eyes quietly fixed on the cups.

"Begin," Shinobu said softly.

Tanjiro moved instantly—but Kanao Tsuyuri was faster. Almost as soon as Shinobu finished speaking, Kanao Tsuyuri's fingers landed on the back of Tanjiro's hand and gently pinned it down.

Tanjiro's hand froze halfway, just an inch from the cup.

"Kamado, your reactions are too slow," Shinobu said with a smile.

Over the next few rounds, no matter how Tanjiro adjusted his rhythm or anticipated the timing, Kanao Tsuyuri always reacted in an instant, either pinning down his hand or grabbing a cup first and splashing the medicine accurately into his face.

"Pfft—" Tanjiro was splashed three times, the medicine dripping from his chin. It wasn't hot, but it tasted bitter.

"Next. Zenitsu."

"Huh? Me?" Zenitsu sat down with a miserable expression.

The result was a foregone conclusion. Kanao Tsuyuri's speed and reactions completely overwhelmed Zenitsu, and his face was drenched before he even touched the edge of a cup.

"Damn it! My turn!" Inosuke sat down, unwilling to accept it, without even taking off his Boar's Head.

"Begin."

Inosuke roared and thrust out both hands—but he was still a step too slow. Kanao Tsuyuri pinned one of his hands with her left, while her right had already picked up a cup and calmly splashed its contents over his mask.

"Aaaah! That doesn't count! I wasn't ready!" Inosuke jumped up.

"A loss is a loss, Inosuke." Shinobu's smile remained unchanged.

Round after round, Tanjiro, Zenitsu and Inosuke were left in a sorry state, while not even the hem of Kanao Tsuyuri's clothes got wet. She remained calm throughout, giving a polite smile each time she splashed someone before quietly waiting for the next round.

"Moyu, would you like to try?" Shinobu suddenly looked at Moyu, who had been watching from the sidelines.

Moyu thought for a moment, then stepped forward and sat down opposite Kanao Tsuyuri.

Kanao Tsuyuri turned her pink eyes toward him, looking a little more focused.

"Begin."

Almost the instant Shinobu spoke, Kanao Tsuyuri's hand moved—but Moyu's hand moved later and arrived first, gently pressing down on the back of hers.

Kanao Tsuyuri stopped. She tried to pull her hand away, but though Moyu's fingers appeared to be pressing lightly, they held firm like an iron clamp.

"Moyu wins," Shinobu announced, approval flashing in her eyes.

In the second round, Kanao Tsuyuri's breathing grew a little longer; she was clearly getting serious. But Moyu's hand arrived almost at the same time and pinned hers down again.

In the third round, Kanao Tsuyuri's fingers twitched in a feint before she made her real move. Moyu's hand followed hers like a shadow, accurately pinning down her wrist once again.

In three rounds, Kanao Tsuyuri hadn't managed to touch a cup even once.

A clear flicker finally appeared in her pink eyes. Was it confusion and... frustration?

"That's enough." Shinobu clapped her hands. "Tanjiro, did you see that? That's the difference in reaction speed. Kanao Tsuyuri has already mastered Breathing Style: Constant, so her body's reactions and coordination are far beyond yours. And Moyu... although he hasn't mastered Constant, his talent is rather unusual."

She looked at Moyu. "But rather than saying your reactions are 'fast,' would it be more accurate to call it 'anticipation'? Had you already 'seen' Kanao Tsuyuri's movements before she made them?"

Moyu nodded. "Something like that."

"That ability is practically cheating." Shinobu chuckled, then grew serious. "Next is full-body training, which is basically hide-and-seek. But you don't need to take part, Moyu. Your strength is already far beyond this stage of training."

She looked at Tanjiro and the other two. "Within the grounds of the Butterfly Mansion, you need to evade Kanao Tsuyuri as she chases you, or try to catch her. The goal is to train your whole-body coordination, explosive power and endurance. Now, begin."

The result went without saying. Having mastered Constant, Kanao Tsuyuri completely outclassed the three in speed, agility and stamina. Tanjiro could just about hold his own thanks to his keen sense of smell, but he would eventually be found. Zenitsu could briefly pull away with a burst of speed from Thunder Breathing, but his endurance couldn't keep up. Inosuke charged around recklessly and was the easiest to spot.

After a full day of training, the three collapsed on the ground, exhausted and covered in medicine and dust, a complete mess.

"Breathing Style: Constant... is so hard..." Tanjiro panted.

"That expressionless woman... how's she so fast...?" Inosuke pounded the ground in frustration.

"I can't go on... I really can't..." Zenitsu lay flat and played dead.

At dinner, Shinobu and Moyu sat apart from the others.

"As for the specific method of training Breathing Style: Constant..." Shinobu explained the deeper principles to Moyu in a low voice. "The key isn't consciously maintaining it, but making it instinctive. You need your body to remember that breathing rhythm, so that even when you're not conscious of it, such as when sleeping, eating or walking, it maintains it automatically..."

Moyu listened quietly, his Six Eyes working at high speed, analyzing, understanding and absorbing every detail. The Six Eyes' powerful analytical and computational abilities were fully engaged.

Early the next morning, when Shinobu came to the courtyard to instruct Moyu, she found him already sitting on the veranda, breathing long and steadily, with faint currents of air seeming to swirl around him.

"Moyu, you..." Shinobu's eyes widened in surprise.

"I think I understand it now." Moyu opened his eyes, a glimmer shifting in their azure depths. "I tried keeping it going all night. I suppose I've... grasped the basics now?"

Shinobu stared blankly for several seconds before giving a wry smile. "Not even a day... You really are a monster."

But her gaze soon grew serious. "Still, this is only the beginning. To fully integrate Constant into combat and every moment of your life, you'll need to keep practicing and consolidating it. Next, you need to..."

She began giving Moyu detailed instruction on how to maintain Constant in different states and maximize the physical enhancement it provided in combat.

Meanwhile, Tanjiro and the other two continued their training, which grew more and more grueling.

Flexibility training, reaction training, hide-and-seek... day after day. Every day they were so exhausted they could barely get up, yet their progress was minimal. In reaction training especially, they still lost more often than they won against Kanao Tsuyuri, and were frequently drenched in medicine.

A few days later, Inosuke and Zenitsu finally began scheming.

"My head hurts! My stomach hurts too! Everything hurts! I can't train today!" Inosuke refused to get out of bed that morning, shouting loudly.

"Me too... I think my old injuries have flared up again... I need to rest..." Zenitsu was wrapped in his blanket, looking weak.

Only Tanjiro got up on time and silently began warming up, even though his whole body ached too.

Aoi went to check on Inosuke and Zenitsu, frowning deeply. "Your pulses are normal, and so are your temperatures... Do you really feel ill?"

"Really, really! I feel awful!" Zenitsu's acting was exaggerated.

"Hmph! If I say it hurts, it hurts!" Inosuke blustered.

Tanjiro returned for a drink of water midway through training and, seeing this, walked over worriedly. "Inosuke, Zenitsu, are you really all right? Should I ask Miss Shinobu to come take a look?"

"No, no, no! Don't!" Zenitsu hastily waved his hands. "A little rest is all we need! Go train, Tanjiro!"

Tanjiro looked at them and hesitated, but said earnestly, "But how will we get stronger if we don't train? And there are all those people hurt by demons... The harder we work, the more people we can save."

His gaze was clear and resolute. "Besides, Miss Shinobu and Miss Kanao Tsuyuri are teaching us so earnestly, and Aoi and the others are working hard to help us train... We can't slack off."

Inosuke pulled the blanket over his head. "Quit nagging! I know!"

Zenitsu turned away and muttered, "But I'm really tired... and I lose every day..."

Just then, Moyu's voice came from the doorway. "Giving up because you're tired, running away because you lose—"

He walked in, his azure eyes sweeping over the two. "Inosuke, don't you shout every day about challenging me? You can't even stick with this little bit of training, and you still want to beat me?"

Inosuke abruptly threw off the blanket and sat up. "Who says I can't stick with it?! I just... I just..."

"You're just scared?" Moyu's tone was flat. "Scared you'll never beat Kanao Tsuyuri, scared you're not actually that strong?"

"Bullshit! I'm not scared of anyone!" Inosuke jumped out of bed, grabbed his mask and put it on. "Fine, I'll train! I'm gonna beat that expressionless woman today!"

That's one taken care of. Moyu looked at Zenitsu.

Zenitsu felt a chill under his gaze. "Wh-what...?"

"Zenitsu," Moyu said, his tone still even, "if you keep this up, no girl will ever like you."

"What?!" Zenitsu felt as if he'd been struck by lightning.

"Someone who's weak, runs away and can't even stick with training," Moyu continued, twisting the knife, "forget Nezuko—no girl would look twice at him. If you run into danger someday, forget protecting anyone else; you'll be lucky to survive yourself."

Zenitsu's face went deathly pale. Nezuko's cute face flashed through his mind, followed by an imagined scene of himself fleeing in disgrace, unable to protect anyone.

"I-I'll train! I'm going to train right now!" Zenitsu scrambled out of bed. "Tanjiro! Wait for me! I want to get stronger too! I'm going to protect little Nezuko! I'm going to become a man girls can rely on!"

Seeing the two of them reinvigorated, Tanjiro breathed a sigh of relief and gave Moyu a grateful look.

However, the good times didn't last. The training grew more intense, especially with the newly added exercise of blowing apart specially made gourds.

These gourds were specially made, with tough surfaces that required tremendous lung capacity and breath control to burst. They started with small ones, only the size of a fist, but even those left Tanjiro and the other two red-faced and dizzy from blowing.

"Ha—ha—hoo—!" Tanjiro blew with all his might, his face flushing bright red. The gourd trembled slightly, but wouldn't break.

"Cough, cough, cough... What kind of lousy gourd is this...?" Zenitsu collapsed on the ground.

"I don't believe it!" Inosuke took a deep breath and blew hard—"Pfft!" The gourd didn't budge, and he nearly passed out himself.

After several days, only Tanjiro had managed to burst one small gourd. Zenitsu and Inosuke had made no progress at all.

Frustration struck again. The monotonous, painful training, with no obvious progress in sight, made the two think of quitting once more.

And so Moyu began his daily "routine"—

In the early morning, when Inosuke refused to get out of bed, Moyu would stand in the doorway and say casually, "Hey, pig, not training today? Looks like you admit you're no match for Kanao Tsuyuri."

Inosuke would spring up instantly. "Who says so?! I'm going right now!"

When Zenitsu slacked off, Moyu would "happen" to chat with a passing attendant. "I hear boys who like to slack off are the most hopeless. No girl would ever like one, right?"

The girls would cover their mouths and laugh. "That's right. They're not cool at all."

Zenitsu would take a critical hit, immediately scramble up and charge toward the training ground.

Shinobu Kocho soon noticed Moyu's method. Amusement flashed in her purple eyes, and she began "playing along" too.

When she saw Inosuke slacking in training, Shinobu would smile and say, "Inosuke, if you can't even stick with this basic training, I'm afraid you won't even be able to keep Tanjiro in sight in the future, much less challenge Moyu."

Inosuke gritted his teeth and trained even harder.

When she saw Zenitsu sighing over a gourd, Shinobu would "casually" say to Aoi, "Aoi, who do you think is more dependable, a boy who trains hard or one who slacks off?"

Aoi put on a stern face. "Of course it's the one who trains hard! Slackers are the worst!"

Tears streamed down Zenitsu's face as he hugged the gourd and kept blowing.

Spurred on by Tanjiro's hard work and perseverance, and Moyu and Shinobu's "mixed doubles," Inosuke and Zenitsu finally managed not to give up again. Though they complained constantly and howled through training, they kept at it day after day.

One afternoon a month later, during reaction training, the following happened.

Tanjiro faced Kanao Tsuyuri again. In the past month, he hadn't won once. But he hadn't lost heart, giving his all every time, then reflecting and making adjustments after each defeat.

This time, he was especially focused. His sense of smell was sharpened to its utmost, catching the faintest flow of air around Kanao Tsuyuri; his ears were alert, listening for the slightest tremor of her muscles; his eyes were fixed on her hand.

"Begin."

Kanao Tsuyuri moved—but this time, Tanjiro moved almost simultaneously! His hand reached the back of Kanao Tsuyuri's a fraction ahead of hers, pinning it down!

Kanao Tsuyuri stopped, and for the first time, clear surprise showed in her pink eyes.

Tanjiro had won.

Instead of splashing the medicine as they normally did in training, he looked at Kanao Tsuyuri and gave her a warm smile. Then he gently picked up the teacup and carefully placed it on top of her head.

The cup stood steady, not a drop spilled.

"Miss Kanao Tsuyuri, thank you for all your guidance," Tanjiro said earnestly.

Kanao Tsuyuri stared at him blankly. The teacup on her head tilted, and she instinctively reached up to steady it. Her usually expressionless face seemed to show the faintest flicker of emotion.

Shinobu Kocho, who was watching nearby, widened her eyes slightly, then smiled with relief.

Moyu leaned against the wall, the corners of his mouth lifting almost imperceptibly. He had "seen" it—in that instant, Tanjiro's breathing rhythm had changed. It had become steadier and deeper, as though it had merged with the surrounding environment.

He had gained a basic grasp of Breathing Style Total Concentration: Constant.

"Tanjiro..." Zenitsu murmured, his eyes full of both envy and frustration.

"Losing to Moyu was bad enough... but now even Tanjiro..." Inosuke clenched his fists, his eyes blazing beneath the Boar's Head. "I can't lose! I absolutely can't lose!"

From that day on, Inosuke trained even more crazily. He stopped complaining and slacking off. Every day, he was the first to reach the training ground and the last to leave, blowing into gourds until his lips cracked and bled without stopping.

Zenitsu was spurred on as well. Seeing Tanjiro's progress and remembering how Moyu and Shinobu Kocho kept telling him, "No girls will like you, you know," he felt a strong sense of crisis well up inside him.

"No... I really can't go on like this..." Clutching a gourd, Zenitsu wore a rarely seen look of determination. "Tanjiro did it, so I... I have to do it too! Otherwise, how can I protect Nezuko? How can I become a hero girls admire?!"

Though he still screamed, complained, and muttered, "This is so hard, I'm so tired, I'm going to die," while training, his hands never stopped moving again.

Moyu watched it all. He continued his own training, fully incorporating Constant into his daily life. Whether walking, eating, resting, or even sleeping, he maintained that special breathing rhythm. He could feel every inch of his body growing stronger, slowly and steadily—his heart and lungs worked like efficient bellows, his blood rushed like a river, and his muscle fibers grew denser and more powerful.

The feeling of growing stronger was solid and clear.

Occasionally, he exchanged insights on training with Shinobu Kocho. The Insect Hashira's views on Breathing Styles and physical development were unique and profound, and Moyu benefited greatly from them. Some of Moyu's insights based on his Six Eyes and Sage Body also often left Shinobu Kocho deep in thought, her violet eyes gleaming with curiosity.

At the Butterfly Mansion, the days passed one by one amid sweat and the scent of medicine. Pain, frustration, breakthroughs, growth... the three boys struggled onward, each on his own path, moving with determination toward becoming a Hashira.