Seeking advantages and leveraging them had always been Shinji's guiding principle. Far from being deterred by Ryūhei Ubuyashiki's failure, the regret woven into Ubuyashiki's notes ignited a bold determination in Shinji to succeed where he had not.
After much deliberation, Shinji decided to temporarily set aside the first step of optimizing "Breathing Techniques" and begin with the second step: transforming "demons."
Ryūhei Ubuyashiki, as a former Demon King, had conducted numerous experiments on demons, some of which Shinji found highly promising. By building on these foundations, he believed he could achieve results in short order.
With his mind made up, Shinji sprang into action.
First, he meticulously reviewed all of Ryūhei Ubuyashiki's experimental notes related to "demons."
The creation of demons was, in a sense, an accident—a product of a unique potion and a specific bloodline colliding by chance, a jest of fate.
Ubuyashiki had tortured the recipe for that special potion out of Muzan Kibutsuji.
Not only the recipe but also a stockpile of the necessary herbs had been amassed in Ubuyashiki's laboratory, all of which Shinji had brought back to the shinobi world.
As for the special bloodline, it belonged to the Ubuyashiki clan.
To eliminate any future threats, Ryūhei Ubuyashiki had personally eradicated his own clan. However, for the sake of his research, he preserved blood and cell samples from the Ubuyashiki clan, which Shinji had also brought back to the shinobi world.
Thus, if Shinji desired, he could follow the notes to cultivate an entirely new "demon" in his experiments.
Of course, his goal wasn't to create a new demon. What he sought was the demon's ability to harness power at the cellular level.
After reviewing all of Ubuyashiki's experimental notes, Shinji began his trials.
He first arranged the herbs listed in the recipe on the laboratory bench, then slowly focused his gaze on the formula.
"What a complex potion…"
Even for a skilled pharmacist like Shinji, his brow furrowed slightly.
The recipe was intricate and convoluted. He couldn't fathom how the physician who treated Muzan Kibutsuji had devised it.
It took a long while for Shinji to fully grasp the properties of the various herbs in the recipe.
Many of these herbs were unique to the Demon Slayer world, rare and unavailable in the shinobi world, leaving Shinji with little room for error. Simply brewing the potion according to the recipe might pose no issue, but improving it was a challenge of the highest order.
Even the most elite pharmacists in the shinobi world—or a team of them—would likely find it impossible.
But Shinji was different. He possessed a pair of Mangekyo Sharingan capable of peering into the branches of fate. With "Izanami's Destiny," he could turn even the slimmest possibility into reality.
Closing his eyes briefly, Shinji snapped them open.
His once-dark irises now glowed a vivid crimson, his pupils shimmering with an otherworldly light—his dojutsu had been activated!
In that moment, countless overlapping shadows appeared in Shinji's vision—branches of fate, possibilities of the future.
Enduring the intense drain on his ocular power, Shinji began searching for the future he desired.
Having mastered the properties of all the herbs in the recipe, he could adjust their proportions to achieve his goal of optimizing the potion.
For instance, one herb called "Heart-Eroding Grass" stimulated blood flow with its domineering properties. Overuse could overwhelm the heart, causing it to stop.
Another, "Gut-Coiling Flower," enhanced appetite and digestion. Excessive consumption could rupture the intestines.
These were less herbs and more poisons.
The recipe was filled with such dual-natured substances, many used in quantities far beyond safe limits. Shinji's task was to reduce these potent drugs to prevent the potion from destroying the user's bodily structure.
However, the recipe was a delicate balance, with the herbs' properties counteracting and enhancing one another. Altering it wasn't a simple matter of reduction—it was a complex system where a single change could disrupt everything. Thus, Shinji resorted to activating "Izanami's Destiny," using his dojutsu to seek the one-in-a-million possibility where reducing the potent drugs still allowed the herbs' properties to achieve perfect harmony.
Countless streams of shimmering illusions flashed before Shinji's eyes, his expression shifting—frowning, pondering, occasionally grimacing.
After a long while, Shinji stumbled, deactivating his dojutsu.
Leaning against the lab bench, he closed his eyes, taking a moment to recover from severe dizziness. Shaking his head lightly, he exhaled a turbid breath. "Not a single success…"
Thanks to his Rinnegan-enhanced ocular power, far stronger than when he developed the Type-4 aging potion, Shinji had peered into over ten thousand branches of fate in one go. Yet, improving the recipe proved even more difficult than he'd imagined—all ten thousand attempts had failed.
As he restored his ocular power, Shinji evaluated his approach, searching for the cause of his failure.
Unbeknownst to him, major powers in the shinobi world, including the five great shinobi villages, were secretly pursuing similar goals.
The allure of demons' vitality and regenerative abilities was simply too great.
However, lacking the original recipe, these powers could only reverse-engineer demons, yielding limited results. Even a scientific genius like Orochimaru had only developed a less effective transformation fluid with unknown side effects.
With the original recipe in hand, Shinji could improve it from the source, and the final results would surely surpass anything the shinobi world's factions could achieve.
Yet, improving the recipe was also exponentially more difficult than their efforts.
Reviewing Ryūhei Ubuyashiki's notes again, Shinji pondered, "Is there a flaw in my approach, or is improving the recipe simply impossible?"
Suddenly, his expression shifted as a realization struck.
He quickly strode to the storage area and retrieved a potted plant, within which bloomed a blue flower.
"The Blue Spider Lily."
Shinji finally understood where he'd gone wrong.
The original recipe didn't include the Blue Spider Lily, as it was the primary ingredient in the antidote that could revert demons to humans.
Though Ryūhei Ubuyashiki had collected the flower, his obsession with immortality meant he never considered using it to become human again, so he had shelved it.
In Shinji's view, the Blue Spider Lily was the key to stabilizing the human form and preventing the potion from destroying the body's structure.