The woman, whose reunion with Yoriichi Tsugikuni had been interrupted, did not complain at all. Instead, she happily wandered off to search for suitable leaves. With her out gathering materials, Li Ke and Yoriichi immediately launched into their deep discussion.
Tanjiro stared wide-eyed at the legendary man who had just spoken his ancestor's name. But just as he was about to speak up and ask a question, Li Ke reached out and firmly pressed down on Tanjiro's head, keeping him quiet.
Right now was the learning time with an expert instructor! Saving the emotional family history lesson for later was much smarter.
"I am really curious about what you were thinking when you developed this specific stance and this particular breath pattern..."
Li Ke struck a stance and adjusted his breathing. He pointed out a mechanical sequence where he couldn't quite grasp Yoriichi's original design intent. Yoriichi took one look at it and immediately answered Li Ke's query.
"Ah, that form isn't supposed to be performed that way. The exact breathing rhythm should actually be like this. It seems Sumiyoshi simply failed to commit this part to memory."
With that, the two men began to passionately trade notes. Li Ke's breadth of knowledge was remarkably vast. Thanks to his experiences entering Genius Mode twice in the past, he had a massive library of concepts unlocked in his mind. As he conversed with Yoriichi, he frequently proposed ideas that Yoriichi had never even considered before.
On the flip side, Yoriichi truly lived up to his title as the undisputed master of breathing styles. Once he understood Li Ke's unique insights, alongside the various derived elemental breathing styles of the current era, he instantly began modifying his original Sun Breathing style on the spot.
As the two debated back and forth, Tanjiro stood to the side and effectively became their live test subject. Every single time the duo cooked up a new theory or wanted to test a modified technique, they would immediately have Tanjiro give it a try.
There was really no other choice. Yoriichi possessed an impossibly vast reservoir of life force, and Li Ke's own physical vitality was equally monstrous. The structural shifts their bodies could easily endure would be completely useless as a reference point for a normal human. Because of that, only Tanjiro—who was relatively normal by comparison—could act as the baseline test subject.
The cooperative workflow yielded incredible results. In just a matter of hours, the two had successfully optimized Sun Breathing into a version perfectly tailored to Tanjiro's unique body, while also baking in several advanced healing properties.
Li Ke benefited immensely from this exchange as well.
"So that's how it works..."
By utilizing Yoriichi's precise respiratory methods to actively regulate his own body's circulation, Li Ke could finally feel the exact mechanics Yoriichi used to instantly stabilize bleeding injuries. Adapting a few of these precise concepts allowed Li Ke to master a way to use specific breathing frequencies to buffer his internal pathways. This made routing high-pressure energy through his heart significantly safer!
"Mmm... this sensation is truly incredible. Yoriichi, you really are an prodigy!"
Li Ke couldn't help but voice his genuine praise. While this couldn't quite compare to the massive, explosive leaps in power he gained under Gol D. Roger's tutelage, Yoriichi's masterful manipulation of minute internal energies was extraordinarily precise and elegant.
If it hadn't been for the fact that Li Ke already tested it—and confirmed that Yoriichi couldn't manipulate standard Qi or blood energy—he would have definitely asked the man to help him refine the way he ran his Blood-Qi Secret Technique!
But there was no helping it. Since Li Ke didn't possess a Demon-Hand, he had to manually control his own wild, raging blood vitality. It was a path that was both a massive detour and a shortcut at the exact same time.
After all, at the end of their progression, the ultimate path of a Berserker was to move toward finer and more precise mastery over their own blood force. The only difference was that Berserkers with a Demon-Hand could essentially cheat, allowing them to tap into that mastered power much earlier...
Li Ke, on the other hand, had to walk this rigorous path right from the very start.
"No, that is not true. You are the real prodigy here..."
Yoriichi spoke with sincerity. The sheer breadth of Li Ke's knowledge and his profound understanding of various martial arts made Yoriichi feel like he was conversing with a living, breathing library. On top of that, Li Ke possessed so many completely different types of powers, yet every single one of them was mastered to perfection.
If Li Ke's aura didn't radiate such immense youth, Yoriichi would have assumed he was looking at an eighty-year-old master. Only an elderly scholar who had dedicated an entire lifetime to nonstop study could possibly command this level of insight and ability.
Yet, Li Ke looked barely in his early twenties. The word 'prodigy' didn't even begin to do him justice.
Because of this, Yoriichi guessed that Li Ke must have come from a highly prestigious, noble family line, combined with being a naturally hardworking and brilliant genius. Only a person born into an elite clan could ever gain access to such an overwhelming wealth of knowledge.
"Hahaha... I'm really no prodigy. I just had some extraordinarily unique encounters, that's all."
Li Ke scratched his head, feeling a bit embarrassed. His massive library of knowledge was purely thanks to the Genius Mode granted to him by the world whenever he eliminated the monsters in this realm. If he had to rely on his own natural ability to fully synthesize and master all of it, he wouldn't be anywhere near this level yet.
During normal times, he was just a regular guy trying his best to learn. He didn't actually retain a massive amount on his own; he usually only remembered specific concepts when someone else brought them up first.
But under the profound baptism of entering Genius Mode twice, all of that information became fully 'mastered' within his mind.
To be completely honest, it was only because the current situation was so grim—and the otherworldly monsters so terrifying—that he was pushing to wrap things up as quickly as possible to avoid any unexpected disasters. Otherwise, his original plan would have been to travel, train, and study for a year or two before coming back to finish off that ultimate monster.
That Genius Mode was simply way too overpowered!
"You two should really stop showering each other with compliments..."
Yoriichi's wife watched the two men trade praises, finding the sight quite amusing. However, her focus was pulled toward a much more important matter.
"The technique you two were discussing earlier... is it officially finished?"
She deeply hated seeing her husband drowning in sorrow even after death because he felt he hadn't fulfilled his life's mission. Naturally, she cared about this breakthrough more than anything.
"A breathing style that carries absolutely zero side effects—and instead actively extends a person's lifespan—is indeed complete. However, due to how difficult it is to master, the final results will likely vary from person to person."
Yoriichi let out a quiet sigh. Creating this wasn't an incredibly grueling task for him. He had been using his own abilities to help care for and regulate his mother's frail health since he was a small child. When he first developed breathing styles in his youth, he had already put a lot of thought into the medicinal side of things.
Now, after collaborating with Li Ke—a literal 'grandmaster' of human physical vitality—and learning a bit of advanced modern medical science, many concepts that used to confuse Yoriichi suddenly clicked into place. The exact type of breathing style they both envisioned was actually brought to life remarkably fast.
This new breathing style didn't require insane natural talent. As long as a person could consciously control their own respiratory patterns, they could practice it. The real catch was the dedication; it required a steady commitment of one to two years before any noticeable physical improvements would show.
Because of this limitation, Li Ke had proposed breaking the system down into several smaller, specialized breathing styles.
The first variation would specifically boost a person's physical blood force and mental focus. This would allow laborers to perform their daily work with much higher efficiency without causing any structural damage to their bodies. The moment their physical limits were reached, running this specific breath would naturally become impossible, forcing them to rest.
The second variation was specifically designed to put a person into an incredibly deep, restful sleep. It was tailored purely to restore mental energy and maximize sleep quality.
Meanwhile, the breathing styles meant for physical repair and body strengthening would be taught as a matching set. This allowed practitioners to actively heal their systems and completely wipe out any minor side effects caused by the first work-focused style.
On top of those, they even cooked up specialized sub-styles: one completely dedicated to restoring kidney health, and another focused purely on maintaining and protecting the stomach.
The core philosophy was brilliant: while mastering the complete, unified breathing style was incredibly daunting, breaking it down into bite-sized pieces meant anyone could learn it without any issues.
"However, everyone's individual physical condition is different, which will make wide-scale promotion quite difficult. Even so, all we really need to do is thoroughly spread these breathing styles until they become an ordinary part of this world. The rest can naturally be left to the countless talents of the future to patch and refine. Once that happens, the Demon Slayer Corps won't even need to focus on hunting demons anymore. They can transition into an organization dedicated purely to researching and developing different breathing styles."
Li Ke never truly believed that hunting demons should be handled like a private, family-run business. The Ubuyashiki clan had completely strayed down the wrong path from the very beginning. What they actually should have done was align themselves with the Shogunate. They should have systematically promoted breathing styles across the entire nation, relentlessly broadcasting that martial power to the public without restriction.
Only by taking an approach like that could Muzan Kibutsuji be backed into a corner and utterly destroyed.
Unfortunately, the Ubuyashiki clan's singular, overwhelming desire was to personally slay Muzan. They feared that spreading the techniques so openly would cause a panicked Muzan to scatter and hide forever, so they would never adopt such a strategy.
Li Ke harbored no such reservations. Besides, right now, nobody even knew where Muzan Kibutsuji was hiding anyway. He felt zero psychological pressure about turning the world upside down.
As for the personal gains from his extensive exchange with Yoriichi?
He walked away with a far more optimized version of Sun Breathing. He also mastered a set of core respiratory tricks that allowed him to actively regulate the volatile, unstable fluctuations of his Blood-Qi Secret Technique while running it. This allowed him to either lock his blood force into a highly stabilized state or force it to circulate at much higher velocities. For Li Ke, this was already more than enough.
To put it plainly, his focus and stamina during active combat had a limit. Reaching this tier of optimization was plenty.
"This is wonderful... Oh, right. Yoriichi, you have roughly one week of time to move around freely. Feel free to take a walk around the Demon Slayer Corps headquarters. If we happen to run into Muzan Kibutsuji by some stroke of luck, I will instantly summon you right back to the front lines."
A thoroughly amused grin spread across Li Ke's face.
The current Tanjiro had officially undergone a massive super-evolution. The customized Sun Breathing style he and Yoriichi had tailored specifically to the boy's physical foundation retained about eighty percent of the original's raw destructive power. However, the deadly physical side effects were now practically negligible.
Li Ke was even starting to plot a grander scheme. He wanted to dress Tanjiro up in clothes identical to Yoriichi's, and maybe even dye the boy's hair a brilliant shade of burgundy.
Under those specific conditions, Li Ke was deeply, profoundly curious to see if Muzan Kibutsuji would actually be able to maintain his composure.
"Understood."
Yoriichi nodded quietly. He had no objections to the arrangement.
Right at that exact moment, the morning sky began to brighten, signaling the arrival of dawn.
However...
"Hmm?"
Li Ke and Yoriichi simultaneously turned their heads toward the distant wooden box where Nezuko had been resting. At the exact same time, both men caught the distinct sound of a powerful, rhythmic respiratory cycle. They could feel a massive, overwhelming life force slowly and deliberately waking up!
The specific frequency of this entity's breathing matched the exact pattern of the ultimate, finalized Sun Breathing style they had just finished creating!
Yet, beneath that familiar rhythm, there were a few incredibly subtle differences.
A highly bizarre, unique variation.
Driven by the sheer force of this breathing melody, the morning sunlight—which should have been soft and faint—suddenly became blindingly intense. Li Ke could clearly sense a continuous, torrential stream of solar energy being forcefully channeled straight into the wooden structure.
"Could it be..."
A sudden, wild theory flashed through Li Ke's mind. But before he could even process it, the wooden box suddenly shattered into countless flying splinters! A tall, imposing figure rose directly from the wreckage. She stood proudly with her back completely turned toward the rising sun, facing them with a profoundly bizarre smile.
Her long hair billowed and danced wildly in the morning air like writhing tentacles. Because she stood directly against the backdrop of the blinding, piercing sunlight, the group couldn't immediately make out the distinct features of her face. However, they knew without a shadow of a doubt that this being was Nezuko. Furthermore, they could all clearly see—
The legendary Ultimate Nezuko was standing tall, confidently hoisting up her loincloth.