"It really is him..."
Black Zetsu was in a somewhat conflicted state.
A conflicted state that was partly amused and partly uneasy.
Although Emiya Shihara's appearance in this era was an unexpected twist, and he had even ultimately turned his back on Black Zetsu back in ancient times, Black Zetsu still missed the days when the two of them had worked together.
This bizarre feeling...
It was much like being unable to bear the sight of someone too dazzling when one was at rock bottom.
Whenever Black Zetsu thought of Emiya Shihara, it invariably recalled the very first time they had met.
Back then...
Emiya Shihara was in the middle of assassinating Indra.
Back then...
Indra still possessed the Three-Tomoe Sharingan.
Back then...
Black Zetsu had assumed some nobody was rushing to their death.
And the result...
That battle had nearly scared Black Zetsu out of its wits.
For Black Zetsu had never imagined that this nobody had acquired a God Tree Remnant, mastered Wood Release and Natural Energy, possessed formidable taijutsu and Kenjutsu, and even had a small Slug by his side—altogether beating a Three-Tomoe Indra to the point where he couldn't even raise his head.
Because Black Zetsu had been tailing Indra in secret and had drawn Emiya Shihara's attention when trying to help Indra, it was only then that Shihara had abandoned the assassination.
Later...
It hadn't managed to escape.
And thus, it had come to know Emiya Shihara.
It also came to learn of Emiya Shihara's ambition: he wanted to destroy the Ninjutsu Sect founded by the Sage of Six Paths.
For as the Sage of Six Paths grew old and frail, the philosophy of the Ninjutsu Sect gradually spread, and certain disciples left the sect to return to their hometowns.
Some sect disciples used Chakra to benefit the local people, while others let greed take root in their hearts and began utilizing Chakra to seize power and profit.
Emiya Shihara was one of the victims.
A certain sect disciple, in order to rob a few jars of fine wine, used the power of Chakra to slaughter an entire village. Shihara had survived only because he happened to have left the village beforehand.
Seeking vengeance against the sect disciples, Emiya Shihara prayed to the God Tree Remnant left behind, ultimately drawing the power of Wood Release directly from it.
The power of Wood Release was indeed formidable...
Yet trying to challenge the Sage of Six Paths with just that was nothing short of a delusional pipe dream!
Black Zetsu had never believed that this pawn, Emiya Shihara, could accomplish anything useful.
In fact, Black Zetsu had hardly paid him any attention thereafter, knowing only that while traveling across the Shinobi World saving lives, he was simultaneously preaching the creed of the medical ninja to the world.
At that time...
Black Zetsu was riding the crest of success.
Its very first plan had succeeded; it had actively instigated Indra to challenge Asura, hoping Indra would strip Asura of his power and thereby awaken the Rinnegan.
Yet Indra had suffered a crushing defeat at Asura's hands.
That maiden attempt had failed swiftly.
And Black Zetsu, previously riding high, retreated into sullen hibernation.
While it was licking its wounds, Emiya Shihara was still out there saving people everywhere, proclaiming that Chakra was a power meant to relieve the world of suffering, rather than a weapon for sect disciples to inflict misery upon humanity.
In that era...
Emiya Shihara truly possessed a prestige that surpassed the Sage of Six Paths.
For the people of that era had always worshipped the God Tree, whereas the Sage of Six Paths had destroyed humanity's faith.
By comparison...
Emiya Shihara, who endlessly devoted himself to saving lives, was profoundly worthy of respect—especially since Shihara, just like everyone else, held faith in the God Tree.
Always with a tiny, slug-like creature resting on his shoulder, Emiya Shihara journeyed across the lands curing the illnesses of ordinary folk. Even the father-and-son duo of the Sage of Six Paths and Asura held boundless admiration for Shihara's convictions.
Emiya Shihara forged the creed of the medical ninja.
Enduring suffering no ordinary person could bear, yet still striving to rescue a world trapped in agony.
Such a benevolent creed...
Naturally earned the admiration of that hypocritical moralizer, the Sage of Six Paths.
Even Black Zetsu...
Had to admit that Emiya Shihara was genuinely a kind and good man.
Naturally.
Adhering to the principle that villains, too, appreciate good people.
Black Zetsu was exceptionally fond of a good person who could be utilized.
In those lonely, desolate years after its plan failed, Black Zetsu felt as though it had found a kindred spirit, tirelessly whispering disparaging remarks about the Sage of Six Paths into Emiya Shihara's ear as together they denounced the sect disciples who abused Chakra to wreak destruction.
Naturally...
Many secrets were shared in the process.
For instance, that the Sage of Six Paths was the source from which Chakra had spread.
In that era, such a fact was hardly top secret; one could generally dig it up simply by interrogating any sect disciple. Yet it sparked Emiya Shihara's curiosity about the Sage of Six Paths.
After the Sage of Six Paths passed away, this fellow Emiya Shihara wanted to dissect the sage's remains, wishing to trace the origin of Chakra so he might find a way to reclaim the Chakra that sect disciples were using to bring suffering to the world.
Black Zetsu knew he wasn't doing it for power.
As a medical ninja, one needed to study various human organs.
Emiya Shihara was also the first person to dissect corpses, all to refine his medical art.
On more than one occasion, Shihara had mentioned to Black Zetsu that he wanted to shatter society's prejudices against surgery, and that upon his death, he would turn his own corpse into a human specimen so future generations could study medicine using his remains—a promise he indeed kept in the future.
Black Zetsu provided the intelligence regarding the location of the Sage of Six Paths' corpse.
Because the Sage's power reached the heavens and spanned the earth, Black Zetsu had dared not approach the body itself, terrified that even in death the Sage still possessed divine might and could sense its presence.
Emiya Shihara had no such scruples.
The fellow cleanly and efficiently stole the corpse of the Sage of Six Paths.
To study the remains, Shihara carried the body to a place abundant in Natural Energy, where he began a long seclusion.
That place was Shikkotsu Forest.
Shikkotsu Forest was filled everywhere with lethal acidic fluid.
Although Shihara had invited Black Zetsu to come along, Black Zetsu wouldn't dare approach the deadly Shikkotsu Forest.
When Emiya Shihara finally re-emerged into the world, a gigantic slug followed at his side; he had already acquired a portion of the Sage's power and successfully transplanted the Rinnegan of the Sage of Six Paths.
Black Zetsu had never dreamed...
That humanity could achieve such results through anatomical research!
That time...
Before Black Zetsu even had the chance to guide Emiya Shihara on how to gather Chakra, Shihara had already made his move!
With a single strike, Emiya Shihara shattered the entire Ninjutsu Sect!
He slaughtered countless sect disciples, reducing the village of the Ninjutsu Sect to a sea of ruins. He was merely a single step away from utterly destroying the sect founded by the Sage of Six Paths!
That was the closest Black Zetsu's grand scheme had ever come to success.
And it was the most satisfying act of revenge Black Zetsu had ever exacted against the Sage of Six Paths!
Not only destroying the Sage's sect in a physical sense, but delivering a devastating, soul-crushing blow to the very spirit of the sect!
Yet in the end...
Emiya Shihara lost to Asura.
Because Shihara had once crossed paths with Asura.
While secretly collecting and processing God Tree Remnants, in a certain village deeply ravaged by those remnants, he had encountered Asura helping the villagers dig wells. Shihara, too, had decided that Asura was a good man.
In the end, through Asura's earnest persuasion, Emiya Shihara chose to trust Asura's promise—believing that Asura would lead humanity to possess greater power to rescue a suffering world.
This man...
Resolved to entrust his dreams to Asura.
Seeking atonement, Emiya Shihara even used the Reincarnation Tensei Jutsu contained within the Rinnegan, bridging Yin and Yang to resurrect the fallen dead from the battle.
Because the Sage's power was immense, Shihara did not die on the spot after casting the Reincarnation Tensei Jutsu; instead, he returned to Shikkotsu Forest to put his affairs in order.
When Emiya Shihara appeared once more, only a crystal coffin containing half a corpse remained, which the Slug entrusted to Asura.
What a hopelessly naive man...
To actually believe Asura's promise...
Yet Emiya Shihara's success also revealed another possibility to Black Zetsu.
Throughout the long, millennium-spanning expanse of time it had lived since then, Black Zetsu had simultaneously worked hard to instigate wars between the descendants of Indra and Asura, while tirelessly spreading the greatness of medical ninjas, hoping someone might master human experimentation just as Emiya Shihara once had.
Come to think of it...
This was also the source of Black Zetsu's frequent confusion.
For it was simultaneously a war-mongering arms dealer and a sanctified apostle striving to spread the creed of healing and saving lives.
That Emiya Shihara's story could continue to be passed down in this era, while the story of the Sage of Six Paths had instead faded into legend, was undeniably thanks in no small part to Black Zetsu's own efforts.
Pity...
Whether through its own machinations or Shihara's methods, Black Zetsu had never again witnessed a glimmer of successful hope.
Precisely because of this...
Black Zetsu missed Emiya Shihara all the more.
For among all the countless schemes it had executed, Emiya Shihara's attempt had been the one that came infinitely close to success.
How regrettable...
If only, back in that era, Emiya Shihara had not trusted Asura.
"Heh heh heh heh..."
A mocking smile surfaced on Black Zetsu's face.
It imagined what manner of regret and shame for his past betrayal would be etched across Shihara's face if they were to meet now!
"Having witnessed these endless ninja wars, will you now regret your own foolishness in trusting Asura back then?"