During this period, Masamichi Yaga had been taking Sōjun Minamoto on various missions.
The new volume of the Jujutsu Guide had already reached the advanced chapters.
It now covered the major family factions within the Jujutsu world—their inherited techniques, key figures, territorial influence, and more.
The information was thorough.
How could something like this circulate so easily? It had clearly crossed into forbidden territory.
Sōjun Minamoto quietly accepted Masamichi Yaga's support.
The edge of his palm hardened and sharpened, turning into a proper hand blade. With a swift motion, he decapitated the Cursed Spirit in front of him, slashing several more times before it froze. With a light push, the spirit crumbled into pieces on the ground.
His right arm then transformed into a spear-like spike, suddenly extending to pierce through every Cursed Spirit lined up before him. The spear retracted instantly, and Sōjun Minamoto flicked his arm, shaking off the blackening, evaporating blood.
This shapeshifting ability was progressing steadily—perfect for clearing out small fry.
He could also take on the appearance of other people or creatures, though that was purely auxiliary. The shape might change, but the essence didn't—it wasn't of much use to him at the moment.
He didn't need to disguise himself.
The effectiveness of transformation relied on physical conditioning—the stronger the body, the sharper and more durable the form, the more convincing the transformation.
Sōjun Minamoto reached out, grabbing the Cursed Spirit's arms.
Got you!
Four more arms sprouted from under his ribs, fists clenched tight, and pounded down in a relentless barrage.
His punches were so fast they left afterimages, and the wind pressure kicked up clouds of dust, engulfing the spirit.
It struggled and screamed as flesh and blood flew. By the end, it was reduced to a pile of meat on the ground, only the two arms he held still intact.
Sōjun Minamoto wiped the blood from the corner of his mouth.
This was the last of the group, and the strongest. It had caused him quite a bit of trouble.
As he watched it dissolve into black mist, the four extra arms retracted into his body.
Being able to create extra organs and limbs gave him an edge against opponents of similar strength—a type of power used to go toe-to-toe with equals.
But what he really needed was a way to defeat stronger enemies... No. Everyone was growing stronger. If someone could beat him, that simply meant they were stronger.
What he truly needed was a path—one that would make him stronger than the strongest. A method to keep evolving.
After some thought, he landed on biomimetics—
The study of biological structure and function.
Nature was full of anomalies. Humans might be the most balanced and stable species—but they weren't the strongest.
There was so much to learn from.
The compound eyes of flies, the echolocation of bats, the infrared sensing of snakes, a dog's sense of smell, an eagle's vision...
What if he could possess all of these?
In short, he wouldn't just evolve—he would become the most perfectly evolved human being.
...
After each mission, Sōjun Minamoto received a decent payout.
Jujutsu Sorcerers were basically low-key rich. As long as they didn't waste money, there was always enough.
The key was: don't waste it!
Sōjun Minamoto spent a fortune acquiring several hawks.
Phase one of the Eagle Eye construction experiment—begins!
He constructed a single eye, composed entirely of flesh and blood, in the palm of his hand.
Creating extra eyes was no longer difficult. He simply copied the original, connected blood vessels and nerves, and adjusted the structure slightly.
His Innate Technique made it all feel effortless.
That was his first safety net: all modifications would be done on this experimental eye. Only if the transformation proved successful and stable over time would he move on to modifying his real eyes.
Once both eyes had been successfully modified and tested further, he would then replicate the transformation in his soul's visual form. That would be the second safety measure.
Lastly, he'd create backups—copies of his original eyes kept on his person. In the event something went wrong, he could restore them immediately. That was the third level of insurance.
...
So, what exactly are the structural differences between a human eye and a hawk's?
Books provided a basic overview, and detailed research materials were readily available.
He bought the hawks for comparative analysis. There was no need for dissection. With Cursed Energy, he could visualize their internal structure directly in his mind.
Humans have one central fovea—the area of highest visual acuity on the retina.
Hawks have two: a central and a lateral fovea, each in different parts of the eye. The central one allows for sharp monocular vision to detect fine movement; the lateral one captures more detail.
On top of that, hawks have a far higher density of photoreceptor cells—up to 1 million per square millimeter compared to just 150,000 in humans.
They can also finely control the muscles shaping their retinas, adjusting the amount of light entering their eyes. Even under bright light, they can still clearly spot distant prey.
And they have a unique "dual-focus" mechanism: by contracting the ciliary muscles, they can simultaneously alter the shape of the lens and the distance between the lens and cornea—adjusting both the corneal curvature and focal range. They can instantly switch from long-distance to short-distance vision.
...
Once he understood the differences and principles, the path forward became clear.
He attempted to construct an additional fovea—and succeeded!
Next, he tried to synchronize its position with the original—failure.
Failure.
Failure.
...
Dozens of failures. Each time, the eye was scrapped and rebuilt. Eventually, he succeeded in gaining usable vision—this time with a nearly spherical range of sight.
But that wasn't enough. He began increasing the number and density of photoreceptors in the fovea.
His vision grew clearer, more sensitive, the colors more vivid—like a sunlit sky after rain.
This entirely new visual experience stirred a subtle excitement in him.
He moved on to reinforcing the ciliary muscle, allowing control over both the lens and cornea.
By contracting the muscle, he could compress or stretch the lens, adjust its shape, shift its position relative to the cornea, and modify the cornea's curvature.
It required simultaneous coordination and precise control—different tissues needed to work together seamlessly. It was extremely difficult.
After a long struggle, he finally managed it—barely.
With his palm facing outward, he narrowed the pupil and clearly saw ants crawling across the courtyard grass, every detail in sharp focus. Then he dilated the pupil, and could still clearly make out the fine cracks in a distant building's outer wall.
It's said hawks can see up to 36 kilometers away. This eye hadn't reached that level yet—coordination between its internal systems was still lacking.
Still, the first experiment was a success!
Next came structural optimization, fine-tuning the cells and tissues.
He wasn't trying to blindly mimic nature. Just achieving one plus one equals two meant nothing to him—he wanted more. Two wasn't enough. He wanted ten. A hundred. A thousand.
Next, he'd incorporate a fly's compound eyes. And that was just the beginning—vision, resolution, color distinction, night vision, underwater sight...
There was still so much to integrate.
But for now, he had to stop.
The repeated construction and destruction of dozens of eyes made from flesh had built up too much pain.
Of all sensations, pain was the one he could endure best. He'd lived with it constantly since childhood—he'd grown used to it.
But flesh doesn't appear out of nowhere. Where does it come from? It's forced out from the body.
He was now visibly thinner than usual—cheeks sunken, fat reserves depleted, muscles dry and wiry. His body fat percentage had dropped dangerously low. His skin looked like decaying wood.
The first principle of flesh crafting: equivalent exchange.
Cursed Energy, flesh, or even the soul—all could serve as materials for creating extra organs or limbs.
But for accurate experimentation, he couldn't rely on Cursed Energy alone. Using it to construct eyes would invalidate the results. Humans weren't like Cursed Spirits, whose bodies were made of curses.
His body was flesh and blood.
Sōjun Minamoto quickly pushed his Cursed Energy into recovery mode. His body began to slowly regenerate.
This experiment had taken a heavier toll than he'd realized. On the surface he seemed fine, but internally, his body had suffered severe depletion. He'd need time to recover fully.
But the outcome was worth it. Successfully constructing a hawk's eye proved he was on the right path—and that it was possible to replicate the advantages of other organisms.
So then, if he could reconstruct other creatures...
Could he eventually go even further?
Could he reconstruct Cursed Spirits?
Could he reconstruct Jujutsu Sorcerers?