"Interesting..."
Li Ke observed Nezuko as she continued to evolve. While Tanjiro practiced the rhythmic movements of Sun Breathing nearby, Li Ke extended his hand toward Nezuko to facilitate the transfer of energy.
Vitality and spiritual power flowed into Nezuko, who began to eagerly absorb the energy Li Ke provided. Li Ke noticed the unique sensation of her strength growing as she channeled his life force.
Tanjiro's expression, however, was a mixture of confusion and concern. Seeing his sister in such a state, combined with the physical strain of his breathing technique, caused his face to flush deeply. He paused his training, gasping for air, and looked at Li Ke with wide eyes.
"Li Ke-sama! What is happening?"
Li Ke remained calm, watching Nezuko carefully as she remained focused on the energy source. "I am providing her with the vitality she needs. She is undergoing a transformation that is difficult to define, and it is far safer for her to absorb this energy than to seek it elsewhere."
Tanjiro struggled to process the scene, but Li Ke's attention soon shifted to something even more unusual. He realized that Nezuko wasn't just absorbing his vitality; her body seemed to be pulling in something from the surrounding environment.
He felt a strange gathering of energy in the air. Suddenly, the Geiger counter Li Ke had been carrying—a precaution he took after encountering the star monster—began to beep rapidly.
Li Ke looked at Nezuko in astonishment. A faint, glowing luminescence had begun to envelop her form. When he looked up at the night sky, he saw that the starlight was significantly more intense than before.
"What is this?"
Li Ke moved Nezuko further away, and the Geiger counter immediately fell silent. Looking back up, the stars seemed to return to their normal brightness. When he brought her back closer, the device blared again, and the starlight intensified once more.
"This is remarkable..."
He initially thought of the concept of 'Stellar Qi,' but the frantic alerts from his device suggested a more scientific explanation. Nezuko appeared to be directly absorbing cosmic radiation from the stars to fuel her transformation.
"Radiation is just another form of Energy, after all. If that's the case..."
Li Ke turned his gaze toward Tanjiro, who was standing nearby looking completely baffled.
"Tanjiro, your sister might not be afraid of sunlight anymore!"
Li Ke's words left Tanjiro completely bewildered. Li Ke pointed up at the starry night sky to explain.
"Your sister is currently absorbing the power of the stars! Countable numbers of those stars out there are exactly like Earth's sun. They just don't light up our world the same way because they are so far away!"
Putting it this way made sense to Tanjiro, but unfortunately, he simply couldn't bring himself to believe it.
Right at that moment, Nezuko let go and dropped from Li Ke's hand. Like a fish slipping off a hook, she fell straight toward the ground.
Before she hit the dirt, her body rapidly shrunk. She changed right back into her eight-year-old form, looking just like a little doll.
"Nezuko!!"
Tanjiro lunged forward. He caught Nezuko in his arms and quickly placed her back into his newly built wooden box. He wanted to make absolutely sure she wouldn't be killed when dawn arrived.
He desperately wanted to believe Li Ke's claim about Nezuko no longer fearing the sun. However, it just sounded too unbelievable. He felt it was much better to play it safe.
"Well, believe whatever you want. But Nezuko is well on her way to becoming the ultimate lifeform."
Li Ke shrugged. He had felt the precise changes happening inside Nezuko. Looking at Tanjiro, he decided not to waste his breath. Some people only believe things when the cold hard facts are staring them in the face. He had seen this happen way too many times.
Instead, he changed the subject.
"Anyway, Tanjiro. There were many parts of your breathing pattern just now that don't suit your body. You should tweak them. For example, during this specific movement, it's better if you take one less breath. Your lungs can't handle the pressure that follows. Forcing it will tear your lungs apart and cause severe lung damage."
Li Ke casually struck a stance. In this position, the body tightly compresses the lungs to force a rapid exchange of oxygen. The downside is that the crushing pressure is incredibly harsh, causing massive strain on the body.
"Huh? Oh, okay."
Tanjiro blinked. He instinctively swung his wooden stick, mimicking Li Ke's posture and adjusting his breathing rhythm as instructed. To his surprise, he instantly felt his body loosen up. Even the power behind his arm swing increased.
"You also need to change this movement. Your breathing frequency can't keep up with it, which will only damage your body."
Li Ke spoke again, demonstrating two more movements.
"Got it."
Tanjiro began to adjust his posture once more. Still, he couldn't quite understand why Li Ke was being so thorough. This was just a dance handed down through his family line. Was it really worth being this serious about it?
"Um, Li Ke-sama... this is just a traditional dance. Do we really need to be this strict about it?"
He finally couldn't help but ask. Li Ke stared at him in utter shock and asked with a completely serious face.
"Are you actually being serious right now?"
"Huh?"
Tanjiro looked completely clueless. Li Ke felt a wave of speechless exhaustion wash over him. He silently sighed, thinking that the boy truly lived up to his reputation of being a blockhead. His brain cells were definitely on a massive delay.
"Swing your blade exactly the way I just told you, matching the rhythm to your breathing technique!"
As soon as Li Ke finished speaking, Tanjiro nodded obediently. He didn't even ask why, showing total, unquestioning trust.
"Understood!"
He swiftly swung his blade. Halfway through the strike, a roaring flame resembling a solar prominence erupted and wrapped around his weapon. With a clean slice, the blade cleaved right through the massive boulder in front of him! Not only that, but the intense heat actually melted the very path the blade had traveled!
Staring at the aftermath of his strike, Tanjiro looked at the weapon in his hands in absolute disbelief. The sheer power of this single move was completely incomparable to his Water Breathing. They belonged to two entirely different dimensions!
"Th-This is..."
Tanjiro's jaw dropped. He looked up at Li Ke, completely stunned that he had just accomplished such a feat.
"Haven't you realized it yet? Your family's traditional dance is actually an incredibly potent breathing technique. However, as powerful as it is, the toll it takes on the human body is immense."
Li Ke crossed his arms. Looking at the melted scoring left behind by Tanjiro, even he couldn't help but feel a bit surprised.
Though he was already amazed that breathing techniques in this world could produce literal visual effects, the demons here possessed literal superpowers, and actual monsters had begun appearing, so this minor detail wasn't really a shock anymore.
Still, the destructive output of Sun Breathing made him click his tongue. While its range and sheer force couldn't match his Dragon Power flames, this was performed by Tanjiro, whose body wasn't even fully compatible with Sun Breathing yet. If it were Yoriichi Tsugikuni executing it, it would be on an entirely different level.
Sun Breathing was strong, but the real monster had always been Yoriichi himself.
This breathing style's immense power was built entirely on pushing the human body beyond its absolute limits!
Only a once-in-a-century prodigy like Yoriichi could use it without any side effects. For someone like Tanjiro, using it seriously a few dozen times would essentially punch his ticket to the afterlife.
If Tanjiro tried to unleash the full, unmitigated power of Sun Breathing right now, he might as well buy a coffin. His physical foundation simply wasn't up to the task.
"This breathing style puts an extraordinary amount of pressure on your lungs. If it's you, and you don't use the modified version I just gave you, you'll be riddled with chronic illnesses after just a few attempts. Use it a few dozen times, and you'll drop dead on the spot."
Li Ke kept his arms crossed. The sheer power of Sun Breathing was undeniable. If he were to combine it with his own Mana Burst or Pyrokinesis, a single strike would probably wipe out every single living soul on an entire street.
Of course, vaporizing reinforced concrete buildings was out of the question—he couldn't pull off anything that absurd just yet.
But this technique, much like his Blood-Qi Secret Technique, was essentially trading your lifespan for power. Even without this breathing style, Li Ke could easily obliterate an entire street's worth of life with a single charged strike anyway.
Furthermore, if he chose to utilize this breathing technique, he would have to stop running his Blood-Qi Secret Technique because the two were fundamentally incompatible! Breathing styles manipulate inhalation to alter blood circulation speed and boost physical strength. Meanwhile, the Blood-Qi Secret Technique directly mutates the body's blood itself, forcing an immediate overwrite of physical functions. They were two entirely different paths.
Comparatively speaking, the Blood-Qi Secret Technique was vastly superior. Breathing styles were simply easier to pick up. His Blood-Qi Secret Technique, on the other hand, was practically a death sentence to learn unless you possessed a Demon-Hand.
When it came to the scaling potential and future development, the Blood-Qi Secret Technique won by a landslide. That was exactly why Li Ke was qualified to critique and alter this ultimate breathing technique.
Once you understood the underlying principle of how breathing styles enhanced the human body, and memorized a few different variations, reverse-engineering the core mechanics became second nature.
Of course, this wasn't completely useless to him. At the very least, Li Ke had learned a few unique ways to stimulate the physical body. He could integrate these specific physical triggers—which his Blood-Qi Secret Technique had previously overlooked—whenever the situation called for a temporary boost.
"So, if you truly want to use this breathing style, your best bet is to stick to the version I taught you and refine it on your own."
Li Ke offered this stern warning as he sized up Tanjiro's scrawny frame.
The modified breathing technique he just provided cut the raw destructive power by nearly half. However, it also reduced the physical damage to Tanjiro's body to an acceptable level. Even so, Li Ke knew the members of the Demon Slayer Corps were a stubborn bunch. No amount of lecturing would ever stop them from throwing themselves into battle against demons.
Still, Li Ke found the whole thing fascinating. Sun Breathing contained a hidden element that none of the other breathing styles possessed.
Healing.
Yes, Sun Breathing gave Li Ke a very bizarre impression. It felt as though someone had intentionally twisted a system meant for medical treatment into a weapon for slaughter. In many of the specific stances, the focus wasn't even on the blade itself. The true, foundational intent of the movements leaked through. For instance, one particular forms looked far more suited for supporting a wounded person than executing a forward thrust.
"When Yoriichi Tsugikuni first developed breathing styles, killing probably wasn't his primary goal at all. What a shame. If Yoriichi hadn't been around, these breathing styles might have eventually evolved into something like Ripple Breathing from JOJO—a perfect martial art for both absolute offense and defense. Truly a missed opportunity."
Li Ke mentally compared the system to JoJo's Ripple Breathing and became absolutely certain of one thing.
In terms of pure cultivation mastery, Ripple Breathing was vastly superior. It extended lifespans, provided medical healing, and packed a serious offensive punch. On top of that, it actively elevated a practitioner's life force and spiritual energy.
Demon Slayer breathing styles were completely outclassed in this regard because anyone who mastered them was practically guaranteed a short life!
Take Shinobu Kocho, for example. Her internal injuries were so severe that even Li Ke's Living Flame couldn't fully mend them. Pushing her breathing technique too hard for too long could literally cause sudden cardiac arrest! If she had trained in Ripple Breathing instead, she would never have faced such a tragic limitation.
However, when it came to immediate destructive power, Ripple Breathing simply couldn't compete.
If you pitted two fighters with identical talent against each other after exactly one year of training, the one using the Demon Slayer breathing style would absolutely crush the Ripple user.
The result would be exactly the same after three years, or even five years!
But after ten years? The tables would turn completely.
By the ten-year mark, the Demon Slayer breathing user would likely be right on the verge of death or permanently crippled. Meanwhile, the Ripple user wouldn't show a single sign of aging! Their combat prowess wouldn't even have reached its absolute peak yet, having only just entered the stage where years of accumulated energy finally burst forth.
"What a real shame. Looking at it this way, it's remarkably similar to the classic feud between the Sword Faction and the Qi Faction of Mount Hua. One offers rapid results, while the other requires a slow, lifetime buildup."
Li Ke stroked his chin. He figured that if he could somehow reverse-engineer Ripple Breathing on his own, it might help alleviate the nasty physical side effects of his Blood-Qi Secret Technique to some degree.
Then again, looking at the limitations of this specific world, creating it out of thin air might not be possible here.
"Does this mean I actually need to summon Yoriichi Tsugikuni so we can research and study this together?"
Li Ke pinched his chin as the idea took root.
Just by pondering the mechanics for a brief moment, he had already envisioned a few ways to adjust his breathing to cushion his organs against the high-velocity friction of his Blood-Qi Secret Technique. He could already see a much more efficient method to channel his volatile blood life force through precise respiratory control.
But these high-level theories were impossible to discuss with Tanjiro. The boy was incredibly hard-headed. He clearly lacked the advanced education needed to understand them. Because of that, Li Ke needed to bring in the most professional expert available.
With a casual flick of his wrist, Li Ke tossed a cluster of Living Flame onto Tanjiro to instantly mend his battered body. Then, he waved his hand again. A brilliant burst of golden light materialized in his palm. Out of the radiance emerged a young man with burgundy hair, matching burgundy eyes, and a profoundly melancholy expression.
He stood right before Li Ke.
"Is this... the living world?"
The moment Yoriichi Tsugikuni appeared, he instinctively scanned his new surroundings. Li Ke immediately sensed a gentle, peaceful aura radiating from him. But beneath that gentleness, he also felt something else.
A distinct sensation of danger.
This caught Li Ke off guard. His overall combat power completely crushed the current Demon Slayer Corps. Yet, the man standing in front of him actually possessed the strength to make him feel threatened. Granted, it was merely an aura of danger. It didn't carry the terrifying, fatal dread he experienced when facing those otherworldly monsters, where a single misstep meant instant death.
"As expected of this world's absolute peak. To think you can actually make me feel a sense of danger."
Li Ke extended his hand in greeting.
"Hello. I am the one responsible for saving the world in this current era. And this boy next to me is the person destined to fulfill your legacy by destroying Muzan Kibutsuji."
When Yoriichi heard the name Muzan Kibutsuji, a sudden flash of intense focus sparked in his eyes. He had spent his entire afterlife drowning in self-blame for failing to eliminate Muzan. Deep down, he desperately desired to finish the job.
"So, you have brought me back from the underworld because you wish for me to help you slay Muzan Kibutsuji?"
Yoriichi gripped the handle of his Nichirin Blade. His gaze filled with absolute resolve. But as he looked closely at Li Ke, the sheer weight of Li Ke's power caused his eyes to widen slightly.
"However, given your immense strength, you should be more than capable of killing Muzan Kibutsuji yourself. Furthermore, your great renown has already reached us in the realm of the dead."
He couldn't help but voice his question. He could clearly feel that Li Ke was a profoundly dangerous individual. It felt as though an infinite reservoir of Energy was coiled up tightly inside his body. While resting in the land of the dead, Yoriichi had often wondered what kind of person Li Ke was to be capable of purging all the demons and monsters from this world.
Now that he was seeing Li Ke with his own eyes, his heart settled. Li Ke was undeniably a man who commanded respect and caution.
Li Ke had no idea how Yoriichi was evaluating him. Instead, he simply laid out his true objective.
"Muzan Kibutsuji is a pathetic coward. Finding him by normal means is practically impossible."
Li Ke spoke with total seriousness.
He genuinely believed that tracking down Muzan would be a logistical nightmare. Knowing that demon's personality, Muzan would happily crawl into a hole and refuse to show his face for centuries.
Even if Muzan hadn't decided to completely go into hiding just yet, he would absolutely turtle up the moment he learned about Li Ke's terrifying existence.
"He will undoubtedly hide. When a creature like him decides to vanish, tracking him down becomes incredibly difficult. However, if we can ensure that every single person learns how to utilize a breathing style, his hiding won't matter anymore. You already know how destructive the current breathing styles are to the human body. If we can work together to develop a brand new breathing style—one that extends a person's lifespan, heals physical illnesses, and radiates the pure, blinding power of sunlight—then Muzan will never be a threat again. Even if he hides and crawls out hundreds of years into the future, humanity will always be ready for him."
Li Ke purposely refrained from mentioning that he wanted Yoriichi to help him optimize his own abilities. He knew that as they researched and built this ultimate breathing style together, those personal breakthroughs would naturally happen along the way.
Furthermore, Li Ke had his own secret motivations for doing this.
If this newly created breathing style could be used in other dimensions, he wouldn't have to worry about the physical health of the girls in his life anymore. Even if world differences prevented it from working in other universes, it would still improve Shinobu Kocho's frail constitution. That way, her breath wouldn't completely give out on her after just a short amount of intense exertion from him.
"This..."
Yoriichi's eyes lit up with intense focus. He immediately realized that Li Ke's proposed plan was an absolutely brilliant idea!
If every single person could master this breathing style, then everyone would essentially become a combat-ready swordsman of the Demon Slayer Corps. Everyone would possess the power to stand up against Muzan Kibutsuji, instead of being instantly wiped out the moment they faced a slight setback.
As for whether people would actually want to learn it? As long as a technique was tied to extending one's lifespan and living longer, there was absolutely no way people would refuse to practice it!
With this strategy, even if Muzan Kibutsuji managed to flee this country entirely, he still wouldn't be able to escape his ultimate doom!
"Very well!"
Yoriichi had absolutely no intention of refusing. He gave his agreement on the spot.
Li Ke let out a soft chuckle. With a casual wave of his hand, a woman suddenly materialized right next to Yoriichi.
The moment Yoriichi laid eyes on her, he threw his arms around her without a single second of hesitation. This woman was none other than his beloved wife, Uta.
"Consider this your employee benefits. For the entire duration of our research and discussion, you will be allowed to stay together with your wife. However, you must absolutely promise me not to step foot outside."
"Huh? Why is that?"
Even though Yoriichi's entire heart and mind were completely focused on his wife, he couldn't help but ask out of sheer curiosity.
The very instant he saw his wife, he had already started planning to take her back to the old countryside home where they used to live together.
"Because Muzan Kibutsuji is an absolute coward. If he catches wind that you have been brought back to life, he will flee the country without a single moment of hesitation."
Yoriichi froze for a second, then let out a helpless, quiet sigh.
"You speak the truth."
In his past life, he had desperately searched for another chance to encounter Muzan Kibutsuji. But the harsh reality was that he could never track him down again!
That creature had spent decades hiding from him. Muzan only dared to send Yoriichi's own brother—who had turned into a demon—to face him when Yoriichi was at the very end of his natural life.
"I understand."
He sighed softly, holding his wife's hand tight. He looked back at Li Ke, and then noticed the young boy who was staring at his hanafuda earrings with wide, curious eyes.
Only now did he realize that the boy in front of him not only wore the exact same earrings as him, but his body also carried the distinct echo of his own breathing style.
"Are you... a descendant of Sumiyoshi Kamado?"
He couldn't help but ask. The moment he looked at Tanjiro, a powerful, overwhelming premonition washed over his soul.
'This child will be the one to finish the task that I failed to accomplish.'
The feeling was so incredibly intense that it made him want to reach out. Tanjiro felt a bizarre, unexplainable connection as well, as if the man standing before him was a reflection of himself from another lifetime.
"He is indeed the one chosen by this era to slay Muzan Kibutsuji. Therefore, while we collaborate on this project, we should also give him some proper guidance. Haven't you noticed? His core presence is remarkably similar to yours."
Li Ke spoke up. Yoriichi didn't answer right away, but his wife spoke in his place.
"Yes, he truly radiates a wonderful, gentle warmth. He feels very much like you, Yoriichi."
Li Ke looked at the woman and remained silent. Instead, he pulled out a jar of sweet fruit wine and set down a few small snacks in front of the lady.
"I must trouble you, Ma'am, to help us gather some tree leaves to use as cups."