The next day.
Early morning.
A corner of a remote island.
Creak~
The sound of a wooden door being pushed open echoed.
A sleepy-eyed Seimei stepped out of the house, yawning as he did.
He glanced toward the east. Although the sun had yet to rise, the faint white glow on the horizon suggested today would be a sunny day.
"Mmm~"
Standing at the doorway, Seimei stretched lazily.
After that, he washed up, popped a few soldier pills (Hyōrōgan) into his mouth, and filled his belly.
Without delay, he headed straight to the coastline and raised a hand to perform the Multi Shadow Clone Technique (Tajū Kage Bunshin no Jutsu).
Poof! Poof! Poof!
With a burst of chakra smoke, a total of 150 shadow clones appeared around him.
Seimei skillfully divided them into groups and sent them off to train independently.
Then, he moved to a secluded beach. After a short pause, he activated his Mangekyō Sharingan.
Immediately, an invisible force began to envelop his body.
This power wasn't just some random ability—it was the external manifestation of "Dominion over the Human Self" (Hito no Go).
Using it, Seimei could control every aspect of his body at will.
Inhale~~~
Taking a deep breath, he suddenly blocked his windpipe and stopped breathing.
Then, he shifted his focus to his skin, maximizing its efficiency in respiration.
Yes—you heard right. His skin.
It's common knowledge that human skin can breathe, but only at about 0.2% the efficiency of lungs—completely insufficient to support a person's needs.
Plus, this method doesn't work underwater.
But if Seimei wanted to use a third method to enhance the efficiency of his physical training, he had to remain underwater for extended periods.
So, his current goal was to evolve his skin to develop underwater breathing capabilities. Maybe not equivalent to lung function, but at least enough to stay submerged for 30 to 60 minutes.
This way, he could use the pressure of deep water to further boost his body's reinforcement process.
Back on Earth, something like this would take millions of years of evolution—or a lab full of tech.
But this was a supernatural world. And Seimei had the OP-level ability "Dominion over the Human Self." With that, this feat wasn't so far-fetched.
Previously, his Mangekyō Sharingan hadn't evolved enough, so this ability wasn't strong enough to support such changes.
Other times, it simply never crossed his mind, or he didn't have the time to try it out.
Now, though, he had both the time and the confidence to complete this breakthrough in a single day.
After all, the goal was just 30 to 60 minutes underwater.
In his previous life, the world record for holding one's breath underwater without assistance was about 24.5 minutes. With his current physique, breaking that record wasn't difficult.
Sure, the stronger the body, the more energy it consumes—but chakra could offset much of that.
All things considered, the difficulty wasn't all that high.
With these thoughts flashing through his mind, Seimei quickly refocused and stepped forward.
His feet entered the sea.
He kept going.
The water reached his knees, then his waist, then shoulders—until even his head disappeared beneath the surface.
Just to be safe, once his head submerged, he didn't go any deeper.
Standing in place underwater, Seimei activated Medical Ninjutsu: Mystical Palm Technique (Shōsen Jutsu) and infused his body with concentrated Yang Release (Yōton) chakra.
Using Dominion over the Human Self, he guided the chakra to stimulate evolution in his skin—specifically to develop underwater respiration.
He didn't need to come up with a detailed system. Life always finds a way.
All he had to do was point it in the right direction and provide the right conditions—then evolution would take care of itself.
Time ticked by.
One minute. Two minutes. Three minutes...
Soon, ten minutes had passed.
This already exceeded the limits of even elite professionals from his past life.
Still, Seimei remained underwater.
Because true evolution only happens when the body is pushed to its absolute limit—only then can it adapt most efficiently.
This was also his first experiment combining passive and active evolution.
If successful, it would give him a solid reference point for future evolutions using deep-sea pressure or other extreme environments.
Drip. Drip.
Unknowingly, five more minutes had passed.
Now at fifteen minutes underwater.
Blub blub~
Suddenly, bubbles rose from Seimei's head.
He was clearly reaching his limit.
But he didn't surface.
Close to the limit doesn't mean at the limit.
Only by reaching the true boundary could his body evolve with maximum efficiency.
Blub blub~
More bubbles appeared—faster and faster.
Finally, at the 20-minute mark, Seimei abruptly stepped back and emerged from the water.
Gasp—Gasp—
He took huge, desperate breaths, as if trying to fill his lungs to the brim.
It took him a full minute to calm his breathing.
Wiping the seawater from his face, he looked determinedly at the distant clones still training.
Then, with another deep breath, he dove back into the sea.
Underwater, he once again used Mystical Palm Technique, this time producing an even denser cluster of Yang Release chakra.
He infused it into his body.
Then, guided by Dominion over the Human Self, he concentrated the chakra into his skin, reinforcing the cells according to his instincts.
Time passed.
This time, Seimei lasted 22 minutes—a clear improvement.
After resting a bit, he began his third underwater evolution attempt.
By combining passive pressure with active chakra stimulation, he could clearly feel progress each time.
And so, Seimei trained like this for an entire day.
By the time night fell, he could remain submerged for an hour and a half.
That's right—not 30 minutes, not 60—a full 90 minutes.
Turns out, he had seriously underestimated both Dominion over the Human Self and the potential of hybrid evolution training.
Under the moonlight…
Splash~
Seimei surfaced once again.
A ball of chakra formed in his palm.
Then, with a push of his hands, he leapt from the water and landed steadily on the ocean surface.
Since he recalled his shadow clones every hour, he wasn't gasping for air like before.
His breathing had quickened slightly—but only just. Without careful observation, it would go unnoticed.
A few flickers of movement, and he returned to the shore.
Fire Release chakra ignited over his body, drying his clothes in an instant.
Feeling more comfortable, he glanced toward the distance at his remaining clones.
Then, with a single thought, he released the Multi Shadow Clone Technique.
Instantly, all clones vanished.
A flood of memory data rushed into Seimei's mind.
He stood there, silently absorbing and digesting the accumulated training experience.
Fifteen minutes later, he opened his eyes.
All that experience and memory had been converted into skill proficiency.
His day's training was basically done.
Now, all that remained was nurturing the Byakugan.
Without wasting time, Seimei disappeared in a blur, heading back to his wooden cabin.
Inhale~~~ Exhale~~~
He took a deep breath, exhaled slowly, and fully calmed his mind.
Sitting cross-legged on the modest wooden bed, he activated the "Samsara Seal of All Things" (Shinra Banshō Fūjin) at his brow and linked it with the Byakugan.
Then, with practiced ease, he began the nurturing process.
This would take about two and a half hours, consuming 2.5 million chakra points, and yielding 12 to 13 points of proficiency.
(End of Chapter)