After dealing with the prisoners of Hōzuki Castle, Uchiha Feiyu gained over a hundred more units of black aura for sacrifice—high-quality ones at that.
The Grass ninja were also delighted. Especially Mui, the warden of Hōzuki Castle: more than half of the refined Origin Pellets Feiyu made were given to this "city-surrendering" warden.
Unfortunately, he celebrated too early.
With a single Du Shen Art, Feiyu took control of Mui completely—giving him no chance at all.
In fact, among the original Grass ninja, Mui was roughly the strongest. After consuming a large number of high-quality Origin Pellets, he progressed even faster than the three Grass leaders, reaching a level comparable to the Third Hokage.
The current Third Hokage was around fifty-plus years old. He wasn't "invincible under heaven," but he was far stronger than his later, older self—among Kage-level fighters, he counted as a true powerhouse.
With Mui added in, Kusagakure now possessed:
one top-tier Kage-level expert,
three solid Kage-level pillars who weren't weak at all,
over a hundred jōnin,
nearly a thousand chunin,
and over two thousand ordinary genin.
Aside from being weaker than the great villages at the genin tier, Kusagakure's strength at every other tier was not inferior to the Five Great Villages—and in many ways, it was stronger than most villages.
And with the great villages either just having fought a major war and being badly depleted, or still tangled in ongoing chaos, Kusagakure had become a force that could no longer be ignored across the ninja world.
At the very least… it now had enough confidence to start capturing ninja from elsewhere.
Even the Five Great Villages would treat such a force cautiously. Before the war ended, none of them would rashly move against Kusagakure.
As for what happened afterward—whether several villages might form a coalition to "punish" Kusa—that had nothing to do with Feiyu.
These Grass ninja were, in the end, merely tools for harvesting sacrifices—artificially cultivated "medicines." If they all died, it wouldn't matter.
Feiyu then turned his attention to the so-called Box of Ultimate Bliss, raising an eyebrow.
"This box… is interesting."
The Box of Ultimate Bliss was rumored to be a treasure created by the Sage of Six Paths, with absurd stories like "whoever opens it can have a wish granted." But Feiyu could tell at a glance that it had little to do with chakra.
True, the box was wrapped in a great deal of energy—but that energy reeked of darkness and blood. With the demonic arts Feiyu had cultivated, he could sense that what clung to the box was less "dark chakra" and more like pure, concentrated resentment.
"It feels like an excellent material for forging a demonic artifact. Come to think of it, I still don't have a truly good magical tool."
The Kusanagi Sword was decent, but in the end, aside from a certain evil-dispelling edge, it was simply a sharp and durable weapon. It was worlds away from truly mystical treasures.
Among the secret techniques inherited from the Shrouding the Heavens path—the secret chapters of the Heaven-Swallowing Demonic Art—there was some knowledge about artifact forging. But that world's forging arts were, frankly, more for show: aside from refining one's own "life-bound" treasure, they couldn't compare to the forging methods of other cultivation worlds—especially since the knowledge Feiyu received was incomplete.
Besides, Feiyu couldn't cultivate the "secret realm" system in the first place, meaning he couldn't create a true life-bound artifact. And the Heaven-Swallowing forging secrets favored the bodies of special physiques as the best "materials," while their methods of refining heavenly treasures were relatively ordinary.
Not to mention: the ninja world didn't really have "heavenly treasures." The Box of Ultimate Bliss was a totally different thing. Who knew what Heaven-Swallowing would refine it into?
After thinking it through, Feiyu made up his mind: he would draw forging knowledge from the Demonic Inheritance Book and turn the Box of Ultimate Bliss into something he could use.
Perfect timing. He had harvested several thousand ninja in Kusagakure—black aura sacrifices were plentiful.
As the black aura on the altar slowly vanished, the Demonic Inheritance Book shook again and transmitted two pieces of information into Feiyu.
This time, what Feiyu asked for was a method to maximize the use of the Box of Ultimate Bliss.
What he received were two inheritances:
One was a method to forge a treasure called the Hunyuan Treasure Box.
The other was a soul-refining art.
The name "Hunyuan Treasure Box" sounded noble, but it was an unmistakably demonic artifact. As for what it did—it could be seen as an upgraded version of the Blood Pool.
The Blood Pool could refine another's bones and blood to strengthen one's bloodline.
But the Hunyuan Treasure Box could refine bones, blood, and soul—cleanly, completely. And the result wasn't merely bloodline enhancement: it strengthened everything—chakra, physical talent, and soul power.
In other words, it was a fully automated alchemical furnace.
Except its "ingredients" were living flesh and blood—living subjects were best.
And the "pills" it produced were far stronger than what the Blood Pool could yield. Toss in an ordinary ninja, and it would refine three items:
soul-origin,
bodily qi-and-blood,
and the ninja's own chakra.
"This really is worthy of the Demonic Inheritance Book. Eight out of ten inheritances teach you how to eat people. But I asked for a battle-boosting artifact—why give me this?"
It was true. Feiyu had realized he was "eating people" with increasing refinement: from the soul-control art, to the blood-swallowing technique, to Heaven-Swallowing… and now the Hunyuan Treasure Box and a soul-refining method—every one of them was an ultimate devouring art.
The soul-refining art resembled the soul-consuming methods of his soul-control technique, but it came from the Soul Clan of the Battle Through the Heavens world—the very same kind of secret art used by the Soul Hall, the people who laughed "heh heh heh" while doing horrific things.
The reason this soul-refining method appeared was simple:
Inside the Box of Ultimate Bliss was an unimaginably vast store of souls.
Feiyu became even more convinced the box had nothing to do with the Sage of Six Paths—because from the perception granted by the soul-refining method, the box contained at least a million souls.
And these weren't ordinary souls, either. At minimum, they had to be "ninja-grade" to be recorded and stored inside the box.
Consider this: in the war, the Five Great Villages plus the smaller ones scraped together only eighty thousand ninja soldiers—and that was after over a decade of peace.
Even pushing the upper bound absurdly high, a single era's living ninja population couldn't exceed two hundred thousand.
In theory, for the box to have gathered nearly a million ninja souls, it would have had to bury the dead across five full generations of ninja.
Realistically, it would require even more—because ninja numbers only truly exploded after the Five Great Villages were founded. Before that, shinobi mostly existed as clans; even searching the entire world, you'd find only tens of thousands.
The Sage of Six Paths spread chakra to the world only about a thousand years ago. No matter how you calculated it, the Box of Ultimate Bliss couldn't have collected nearly a million ninja souls within a millennium.
"Maybe this thing existed long, long before Kaguya. Otherwise it couldn't have devoured so many souls. And… it feels more like something from an onmyōji-style system."
Devouring souls. Absorbing resentment. Creating a being like "Satori" that could sense hostility…
That kind of approach was rare in the chakra system, but in onmyō arts it was basic.
But soon, Feiyu stopped worrying about which "immortal" had created the box.
He sat cross-legged atop it and began refining it.
Though he had no complete cultivation system, the chakra in Feiyu's body had been tempered through many secret arts. Its nature had changed drastically—approaching something like legendary "mana." At least, it was sufficient for refining and forging the box.
As his chakra slowly seeped into the enormous chest beneath him, he also activated the soul-refining art. The million souls sealed inside the box began to be refined into soul-energy.
A million souls sounded enormous, but their quality wasn't high. Most importantly, too much time had passed—the energy within them had leaked away severely.
Worse still, the Box of Ultimate Bliss was drenched in baleful aura. The souls stored within were heavily contaminated, filled with impurities. Nearly 99.9% of them were resentment, leaving only a tiny trace of pure soul-energy.
Feiyu's soul-refining art—borrowed from the Soul Clan—could repeatedly refine the souls and purge the resentment completely. But as the resentment was ground away, waste was unavoidable.
Especially with souls so saturated in resentment… despite the terrifying quantity, after full refinement, less than one-thousandth remained as pure soul-energy.
In the end, what was left amounted to soul-energy equivalent to only a few hundred people.
That wasn't weak—Feiyu's own soul-energy was only around that level, comparable to a few hundred people.
Chakra wasn't even a complete cultivation system; it was closer to an "ability." It naturally grew with body and mind, but lacked a true method for systematically cultivating the soul.
So even Kage-level experts, nourished by chakra, might only possess souls ten or dozens of times stronger than an ordinary person.
Feiyu's soul-energy was as strong as it was only because many demonic arts had "propped it up"—especially the soul-consuming aspects of his techniques, and Heaven-Swallowing's refinement of essence, qi, and spirit.
But neither his soul-control art nor Heaven-Swallowing was a dedicated soul-cultivation method.
His soul-control art didn't strengthen "soul-energy" directly; it strengthened "innate qi," and conversion efficiency was abysmal.
Heaven-Swallowing's greatest effect was physique transformation; soul growth was only a side benefit.
That was why Feiyu's soul-energy, though strong, still lagged behind his physical foundation.
Now, however, he had a chance to make up for it.
While refining the Box of Ultimate Bliss, Feiyu absorbed the purified soul-energy. He felt his soul and body enter a strange, wondrous state.
He didn't know how much time passed. Then he felt as if he became incredibly light. With a gentle leap, he broke free of some invisible restraint and drifted into the air.
Lowering his head, Feiyu saw his own body still sitting atop the box.
Only then did it dawn on him: his soul had left his body.
Feiyu had once practiced the Spirit Transformation Technique. Even though he hadn't cared much for it, with his shocking foundation he mastered it easily.
But it wasn't very useful to him. A body without its soul was defenseless—so he never used it.
"However… I'm not in a Spirit Transformation state right now… my body is still refining the box beneath me!"
"What is this? The legendary 'no-thought' state?"
When a shinobi used Spirit Transformation, the body became senseless—like a vegetable.
But Feiyu could clearly feel that his body was still refining the box. This wasn't Spirit Transformation.
And he could also tell: his soul carried no chakra at all. It didn't have the chakra shell that Spirit Transformation created.
He didn't know what state he was in, but he could sense it wasn't a bad thing.
A moment later, he felt a pull from the body below. In an instant, his soul returned to his flesh—and he sensed his soul had become much more stable.
After absorbing so much soul-energy, Feiyu had felt his perception, reaction speed, and chakra control leap forward—but he also felt a floating, unreal lightness.
After this change, he instead felt grounded and steady.
Exhaling slowly, Feiyu showed a hint of delight.
In truth, his rapid growth had always been accompanied by heavy hidden risks.
Demonic arts were often riddled with problems like reckless, shortcut-driven advancement. And both the Uchiha bloodline and the chakra system were not "stable foundations" either—if anything, they were demonic even among demonic paths.
Feiyu's cultivation had always felt like walking a tightrope.
His power surged, but his foundation was far from solid—only stronger than ordinary shinobi.
If he reached a certain level, he might hit a bottleneck he couldn't pass.
"This change in the soul at least tempered my foundation a little…"
"But I can't worry about that now. By the time I hit a bottleneck, my strength will already be far beyond the Ōtsutsuki."
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