As a veteran ninja who had weathered multiple wars, Aburame Shibi initially thought he'd seen it all and could handle anything with stoic composure. Yet, after enduring Habara's brief but bizarre 'talk therapy' session prior to the injection, he suddenly felt, for reasons he couldn't quite pinpoint, a bit… needle-shy.
But this was hardly the time for regrets or refusals.
Habara, despite his utter lack of formal nursing experience, moved with the practiced ease of a near-retired, highly efficient head nurse. The needle found Shibi's shoulder, administered the dose, and was withdrawn before Shibi registered any distinct pain. Habara was already finished, capping the syringe… In every practical sense, it was a perfectly executed intramuscular injection.
"Is that… it?" Shibi asked hesitantly, feeling a wave of uncertainty highly uncharacteristic for a Jōnin of his caliber.
"Of course. Do you have any doubts?" Habara replied smoothly.
"Well, I heard Tenzo's experience during his injection was… rather complex?" Shibi inquired carefully.
"Two main factors contribute to that," Habara explained patiently. "First, Tenzo is slightly different compared to the average ninja. This inherent difference means he often requires special consideration and treatment. Crucially, regarding this specific matter, his body's interaction with the vaccine is unlike yours; his system doesn't trigger the same kind of immediate, intense activation upon injection that yours likely wouldn't either, especially not with this version. Second, scientific development involves iteration and evolution. Compared to the earlier prototypes Tenzo was subjected to, the vaccine formula is much more mature and stable now."
"Understood," Shibi nodded slowly. "So, does that mean nothing abnormal will happen to me?"
"Not exactly," Habara corrected, shifting into his 'doctor's advice' mode. "Over the next three to five days, you'll likely experience a low-grade fever, accompanied by minor secondary effects like muscle soreness, fatigue, and a general lack of energy. During this period, you should avoid frequent chakra use—or, to be safest, avoid using chakra altogether if possible."
In reality, using chakra wouldn't necessarily interfere with the vaccine taking effect. Habara's warning stemmed purely from caution; chakra was a notoriously unpredictable element, and who knew what unforeseen chemical reactions it might trigger in combination with the new substance integrating into Shibi's system.
As it turned out, thanks in no small part to Tenzo's invaluable, if involuntary, contributions as the primary test subject, this second 'vaccine' administration was also deemed a success. However, likely due to careful dosage control, or perhaps because of the individual physiological differences Habara had mentioned, the effect on Aburame Shibi was far less pronounced than it had been on Tenzo—significantly less, in fact.
Subsequent comprehensive evaluation—factoring in chakra intensity, jutsu power output, and other metrics—showed that the vaccine provided Shibi with an overall performance enhancement ranging between 25% and 30%. Furthermore, since Shibi was already a fully mature ninja, there was likely very little room for this boost to increase further alongside his own natural development.
Nevertheless, for Shibi himself, the result was incredibly satisfactory. The enhancement provided by the vaccine felt fundamentally different from external power boosts like those derived from the experimental 'Infinite Library' project. This newfound strength felt entirely integrated, completely his own, which was undoubtedly far more gratifying and reliable in the long run. His combat power was now demonstrably incomparable to his level during the Third Shinobi World War.
The successive successes with both Tenzo and Shibi allowed the research project and its results to be formally registered with the Third Hokage. However, considering the existing terminology deeply ingrained in the shinobi world's common knowledge, and aiming for stylistic consistency, Habara couldn't realistically label his creation a 'vaccine' in the official records. Thus, his internal designation YT57-09 received its formal, public-facing designation: the Curse Mark of Man.
For Habara, the greatest personal takeaway from this entire line of research was a renewed, crystal-clear appreciation for the importance of quantifiable metrics. This brought him back to his original, more personal goal: Sage Mode.
As is widely understood, Sage Chakra—the fuel for Sage Mode—is composed of physical energy, spiritual energy, and natural energy, mixed in a precise 1:1:1 ratio. If a ninja can master the production of large quantities of Sage Chakra, they can sustain the powerful, enhanced state known as Sage Mode for extended periods.
The core difficulty lies in quantifying these three distinct energy components. How much constitutes 'one part' spiritual energy? How much is 'one part' physical energy? And, most crucially, how much is 'one part' of the external, untamed natural energy? There are no convenient rulers, scales, or measuring cups available for such esoteric forces.
Combining the two internal components—physical and spiritual energy—is simple, almost instinctual for ninja; they do it constantly to create their standard chakra. Precise control isn't necessary in that process; leftover energy of one type or the other isn't a significant issue. But introducing a third, fundamentally external component—natural energy—and mixing it in perfect proportion is an entirely different, far more challenging proposition. Natural energy doesn't integrate as readily or as forgivingly as the body's own energies do.
To use a more specific analogy: creating Sage Chakra manually is like trying to tune a complex musical instrument purely by ear, relying solely on one's innate talent. Some individuals are hopelessly tone-deaf (like those unfortunate souls who attempted Senjutsu training at Mount Myōboku and were permanently turned into toad statues); no matter how hard they try, even for ten thousand years, they'll never achieve the correct resonance. Some possess a degree of musical sense (like Jiraiya); through decades of painstaking trial, error, and gradual refinement, they can eventually fumble their way towards a functional, if imperfect, tuning. And then there are those blessed with perfect pitch (like Uzumaki Naruto); they hear the target harmony once, make an almost instinctive adjustment, and the instrument is perfectly tuned in moments.
So, where did Habara fit on this spectrum? What was his innate talent for this delicate balancing act?
Here, Habara posed a counter-question to the universe: Why must I rely on manual tuning by ear? Why can't I simply invent a tuning device?
That very night, after returning home, Habara began modifying the complex sealing formulae already embedded within his own chakra network—specifically, those sophisticated arrays related to his adaptations of the Technique of Six Rens and the Arc Gradient Sevenfold Amplification. Building upon the insights gained from his recent research, particularly the emphasis on quantifiable flow and balance, he implemented his conceptual 'tuning device.'
He established a new, intricate sealing formula directly upon his main chakra pathway. Its primary function was elegant in concept: it was designed to draw in both his standard chakra and external natural energy simultaneously, ensuring they entered the seal's matrix at precisely the same 'flow rate.' Once inside the seal, his standard chakra was automatically reverse-engineered, broken down into its constituent physical and spiritual energies. Natural energy, flowing in at an equal rate, was then introduced into this mix. Within the controlled environment of the seal's matrix, the ratio of the three essential components—physical, spiritual, and natural—would therefore be maintained precisely at the required 1:1:1.
The sealing formula itself was constructed entirely from potent Magnet Release chakra. This unusual composition served two critical purposes. Firstly, the incredibly powerful magnetic field generated by the seal provided absolute containment, preventing the leakage of the three volatile energy types during the mixing process and ensuring their proportions remained exact. Secondly, this strong magnetic constraint could instantly force the constituent energies—physical, spiritual, and natural—into a stable, unified recombination, creating the desired end product.
Perhaps because he'd conducted experiments on others quite frequently of late, when it came time for Habara to operate on himself, he found himself remarkably calm. After all, the potential risks to his own well-practiced and resilient system couldn't possibly be greater than the dangers Tenzo had already bravely endured.
He took a deep, centering breath and activated the newly modified seal.
The next moment, an immense, resonant power surged through his being.
He immediately felt a potent, explosively powerful, yet simultaneously remarkably refined and stable chakra begin to flow through his pathways. This was definitively not the crude, slightly volatile mixture of standard chakra and natural energy he'd occasionally felt before when simply absorbing ambient natural energy.
"Isn't this… Sage Chakra?"
No one was present to answer Habara's internally voiced question, but perhaps it didn't need an external answer. The sensation itself was undeniable.
However, achieving the intense pressure, rapid flow rate, and powerful magnetic containment necessary for the seal's function came at a calculated cost: Habara had effectively sacrificed fine chakra control over the rest of his body's energy systems. Consequently, as the Sage Chakra flowed, he was experiencing significant, uncontrolled chakra leakage from his entire system, bleeding energy into the surrounding air.
Every second, he was technically wasting large amounts of his standard chakra reserves. But… his reserves were vast. What was a little waste in the grand scheme of things? Compared to what he had gained—the ability to generate Sage Chakra—the price was negligible. The leakage was acceptable; the result was worth it.
He clenched his fist, observing the faint aura now shimmering around it. Then, he lightly tapped the sturdy wooden wall in front of him. Unexpectedly, the wall crumbled effortlessly under the feather-light touch, leaving a hole the size of a washbasin punched clean through it. Such destructive force was normally trivial for Habara to achieve with intent, but just now, he truly had only tapped it gently, gently.
"Feels like… it wasn't that hard after all," Habara murmured, a slow smile spreading across his face. He looked first at his palm, then at the distinct, ring-shaped field of palpable chakra now visible on the ground around him—strands of potent energy rotating softly like a gentle wind, with his body as the axis. It looked serene, yet felt incredibly sharp and powerful.
He had solved the problem of creating Sage Chakra reliably. The hurdle remaining between this achievement and true, sustainable Sage Mode seemed to be solely the challenge of 'how to produce it in large quantities.' It was now a matter of scaling up—a process where quantitative change would eventually lead to a qualitative transformation.
So, how could Habara solve this production bottleneck? The path seemed conceptually straightforward, if technically demanding: while rigorously maintaining the 1:1:1 ratio, he simply needed to increase the energy flow speed through the seal, increase the volume of energy processed per second, and further strengthen the magnetic containment field to handle the greater throughput.
Compared to the sometimes grotesque transformations and exaggerated combat power increases offered by Orochimaru's Heaven and Earth Curse Marks—boosts that could multiply a user's strength several or even ten times over—the effect of Habara's 'Curse Mark of Man' wasn't particularly boast-worthy in raw numbers. But its crucial advantage lay in its near-harmlessness and stability; users didn't risk literally tearing themselves apart from uncontrolled power surges each time they activated it, a common peril for those bearing Orochimaru's volatile gifts. Habara's creation represented a different philosophy: lower immediate gain, vastly lower burden and risk; the user wouldn't gamble their life for power. Orochimaru offered high gain, extreme risk; play around too much with that fire, and you inevitably get burned, often fatally.
A reasonable inference followed from Habara's successful trials: compared to its application on fully mature adult ninja like Shibi, his Curse Mark would likely prove significantly more effective when administered to younger ninja whose bodies and chakra systems were still actively developing and more adaptable. To verify this possibility, Habara's Curse Mark of Man already had new, younger recipients lined up for testing.
Surveying the tangible field of Sage Chakra swirling gently around him, Habara couldn't help but let his smile widen… This was progress.