Two and a half hours later...
The Byakugan nurturing session was complete.
By now, it was deep into the night.
Seimei, utterly exhausted, dragged his body back to the wooden cabin.
Soon after, faint snores echoed from within.
By the usual cycle, this should've been his tenth and final day of intensive training before returning to the village for rest. Normally, today would mark the end of his retreat.
However, during his recent physical transformation, he had already spent half a day relaxing on the island.
So, he still had enough energy left to keep going.
Just in time, too—his newly acquired Reika no Jutsu (Spirit Transformation Technique) had only just been engraved onto his skill panel. He needed more attempts to fully grasp it.
Thus, Seimei decided to keep training for a few more days. He'd only take a proper break once Namikaze Minato contacted him for action.
The night passed without incident.
---
The Next Morning
Seimei woke up early, quickly ate a few enhanced hyōrōgan (military ration pills) to fill his stomach, and jumped right into training.
Even though the 286,000 chakra points he'd saved from mastering Fūton: Tsubasa no Kaze (Wind Release: Wings of Wind) weren't quite enough, he didn't rush to allocate more chakra into the Reika no Jutsu.
First, he needed to clearly understand its chakra drain before making further investments.
The same logic applied to his body enhancements.
For now, he couldn't dive into the deeper ocean zones, so the chakra he'd already invested was sufficient.
No need to rush into more just yet.
Everything remained on track.
This approach saved him quite a bit of time and effort.
So, Seimei kept to his training cycle: every hour, he dove into the water, reclaimed a shadow clone, and completed another training round—repeating this over and over.
From before sunrise to after sunset, he trained nonstop for over ten hours before finally stopping.
Under the moonlight, he sat atop the giant boulder in the island's center, reviewing the day's progress.
Other techniques aside, Reika no Jutsu was different.
After a full day of practice and 286,000 chakra points spent, he'd finally succeeded in unlocking the technique—and his proficiency jumped straight to Level 2.
Opening his panel, Seimei estimated the average chakra cost per skill point, discounting pre-initiation expenses.
His conclusion: to gain one point of mastery in this jutsu, he needed to spend roughly 500 chakra points.
And this was after increasing his Chakra Control to Level 8, which reduced chakra usage by 15%.
A month ago, before his improvements, the cost would've been even higher.
No doubt about it—this technique was beyond the scope of ordinary S-rank jutsu.
Why? As he'd already guessed yesterday, when shadow clones practiced the technique, the projected soul couldn't efficiently use their chakra.
As a result, despite burning the same amount of chakra, the skill mastery gained was only about half that of a normal S-rank jutsu.
Still, since this method saved time for his main body, Seimei could live with the trade-off.
After all, this was a one-of-a-kind jutsu. High chakra consumption wasn't a deal-breaker.
"Phew…"
Letting out a breath, Seimei steadied his thoughts and prepared to test the jutsu.
While he didn't care much about its combat potential, now that he'd learned it, he needed to understand its capabilities inside and out.
With that in mind, he raised his hands and performed the hand seals with precision.
Then, he closed his eyes. Chakra surged from his body.
Moments later, a faintly glowing, transparent figure drifted up from the top of his head—floating mid-air.
It was none other than Seimei's soul.
What stood out was that his spirit didn't match his current youthful body. It appeared in the form of his previous life's adult self, with just a few features from this life mixed in.
For example—his Eternal Mangekyō Sharingan.
Seeing his own image, Seimei immediately decided: Until I reach adulthood, I won't use this jutsu in front of anyone.
After all, a soul that doesn't match the body raises serious questions.
If someone merely suspected he used forbidden techniques like Orochimaru—transferring souls between bodies—that was manageable. At worst, he'd be branded a rogue shinobi and thrown into the "villain" category.
But if someone realized he wasn't even from this world...
That would be a disaster.
So, Seimei made a firm decision: Until I'm an adult, no public use of this jutsu. Even in private, extreme caution is needed.
Why "adulthood"? Simple.
He'd noticed early on that as time passed, his current body's appearance was slowly shifting to resemble his previous life's.
He didn't know if it was a coincidence, subconscious spiritual influence, or if this body was a multiversal counterpart of his original.
Either way, once he matured, his appearance would likely match his past self closely enough that the mismatch wouldn't be noticeable anymore.
Then, the jutsu could be used more freely.
Shaking off those thoughts, Seimei turned his focus to his soul's abilities.
First off—due to low proficiency—his spiritual form could only carry about 20% of his total chakra.
Also, to move while in spirit form, he had to constantly consume chakra. The faster he moved, the more chakra it burned.
In short: his stamina was very limited in this state.
On the plus side, once his soul was activated, his sensory abilities skyrocketed.
Floating midair, he closed his eyes and scanned the surroundings.
After a few seconds, he opened them again.
Rough estimate? At just Level 2, Reika no Jutsu amplified his sensory range tenfold.
Against specific chakra signatures, that detection range could increase by over ten times again.
With this, combined with the Byakugan's kilometer-wide 360-degree vision, his scouting abilities were now elite-tier.
Next, its offensive capability.
As a spirit, he could invade an enemy's mental world, directly attacking their psyche. At best, this would drive them insane. At worst, it could kill them on the spot.
Additionally, he could suppress a target's soul and possess or control them.
This made infiltration and sabotage easy—especially when chaos needed to be sown from within enemy lines.
In short, its potential was immense.
But of course, it wasn't without its weaknesses.
First: while casting the jutsu, his physical body became immobile—an easy target for enemies.
Second: attacking a person's soul wasn't without risk.
If the target had fūinjutsu (sealing techniques) that bound souls, or genjutsu that affected the spirit, then the spiritual battle could backfire.
Losing such a fight could result in spiritual damage—or worse, obliteration of the soul, leaving his body a lifeless husk.
Third: chakra consumption.
Moving, fighting—everything burned through chakra rapidly. If something went wrong, or if his calculations were off, and he ran out of chakra before reuniting with his body…
His spirit would be erased by the material world.
An extremely serious risk.
And there was one more thing: learning this jutsu itself was dangerous.
Thanks to his skill panel and systematic training, he could level it up safely—but others? Without those advantages, they might die mid-training.
The failure rate was not low.
That's why the jutsu had been classified as kinjutsu (forbidden technique).
As these thoughts passed through his mind, Seimei continued testing his soul form's properties.
Once everything was confirmed, he deactivated the jutsu and returned to his body.
His eyes opened again in an instant.
He noticed something: his body felt a bit... off.
Another flaw of Reika no Jutsu: it subtly reduced the harmony between soul and body.
For most people, this might not matter.
But for a transmigrator like Seimei, it was critical.
This body wasn't originally his. Overusing the jutsu could cause severe discord between the two—leading to unpredictable consequences.
Fortunately, he'd already decided not to use the jutsu until he came of age.
With the testing over, Seimei took a deep breath and looked up at the moon.
Time for his final task of the day—nurturing the Byakugan!
The process was the same as usual: two and a half hours, 2.5 million chakra points spent, and a 12-point boost in Byakugan mastery.
With that, Seimei's day of training was officially complete.
Wasting no time, he cleaned up quickly and returned to his cabin for rest.
Seconds ticked by.
Soon enough, faint snoring once again filled the quiet night.
(End of Chapter)