After the two Sharingan were successfully implanted, Yukiko began monitoring Shisui's condition. She attached various auxiliary instruments to him, testing his blood pressure, blood oxygen, heart rate, cell activity, and so on, to ensure no unforeseen complications arose.
Once all the equipment was in place, all that was left... was to wait.
To wait for the eye that once belonged to Uchiha Kōfū to awaken within Shisui—and evolve into an Eternal Mangekyō Sharingan.
Through their recent research on the Sharingan, their understanding of the eye had deepened significantly.
The so-called fusion for the Eternal Mangekyo Sharingan involved one of the two Mangekyo Sharingan users, who were blood relatives, acting as the host for the fusion. This host would provide a stable and continuous supply of chakra for the Eternal Mangekyo Sharingan's integration, allowing the Mangekyo in their eye socket to absorb the dōjutsu power of the previous Mangekyo that remained within their body.
When both streams of dōjutsu power fully merged, the Eternal Mangekyo Sharingan would be born.
Therefore, even if Shisui's original Mangekyo was currently in Yoru's eye, Shisui could still awaken the Eternal Mangekyo Sharingan, because the 'source' of the dōjutsu power remained within Shisui's body.
...
Shortly after the Three-Tomoe Sharingan was transplanted, it began spinning rapidly in Shisui's eye socket. In the span of a few breaths, the tomoe fused and twisted into a unique Mangekyō pattern.
As expected, Uchiha Kōfū had awakened his own Mangekyō before his death. That was why, once implanted, the eye in Shisui's socket could evolve.
As for the specific ability that Kōfū's Mangekyō held... Yoru didn't yet know.
The crimson Mangekyō spun continuously, absorbing the lingering dōjutsu power from Shisui's original Mangekyō, stored within his body.
The fusion would take some time—after all, even in the original story, Sasuke was bedridden for a while after fusing his eyes.
But this case was different.
Shisui already possessed one Eternal Mangekyō. Because the chakra frequencies were aligned, the evolution of the second eye progressed much faster.
In just two hours, Shisui's right eye had fully evolved.
Now, a pair of fully awakened Eternal Mangekyō Sharingan spun silently in his eyes. Their immense chakra pressure was enough to make even Yoru, who had extensive experience with Mangekyō, feel a twinge of awe.
Only when both eyes reached Eternal status could a true Uchiha wield the full might of the Sharingan—and now, the second set of Eternal eyes in the shinobi world had been born in Shisui.
"So this is... my father's power," Shisui murmured, voice low.
He could feel it clearly.
An ocean of chakra flowed through his vision—endless, unyielding, impossibly vast. This was power that wouldn't run dry.
However, because his left eye's Kotoamatsukami was still in Yoru's possession, the Mangekyō ability that awakened in that socket wasn't Kotoamatsukami—it was something else entirely:
Tsukuyomi, the most fearsome genjutsu of them all.
And in the right eye—the black flames of Amaterasu, the ultimate physical attack.
With these eyes... could I actually defeat—
Shisui instinctively glanced toward Yoru, who stood nearby with a half-smile. The memory of that "artistic film" threat flashed in his mind.
...That thought vanished from his head in under a second.
"Magnificent eyes, truly," Yoru said smoothly. "But this is only the beginning, Shisui-kun."
"The beginning...? Of what, exactly?" Shisui asked warily.
To him, even a Uchiha with Three-Tomoe Sharingan was considered a top-tier shinobi.
A Mangekyō user was on par with a Kage.
And an Eternal Mangekyō... that was the power of the ancients—the very force that ended the Warring States Period.
Such power could reshape the ninja world.
And yet, to Yoru, this was just the starting point?
"Have you ever gone to the Uchiha's Naka Shrine after awakening your Eternal Mangekyō?"
Yoru's voice was calm as he stared at Shisui.
"There's something important left behind there—an ancient inheritance from the founder of ninshū himself."
"The Uchiha's Stone Tablet…" Shisui murmured, the memory coming back to him. "I remember… something written on it…"
"One God sought peace, creating yin and yang, two opposing forces. They combine to form all things in creation..."
"So you've seen it. Good. That makes this simpler," Yoru said with a knowing smile. "This principle doesn't just apply to the world—it applies to your eyes as well."
According to classified intel Yoru had uncovered, if someone with the Eternal Mangekyō Sharingan could fuse that power with an equivalent, yet opposite force, they could manifest the power of All Creation—Shinra Banshō.
This fusion would allow the Eternal Mangekyō to undergo one final evolution:
Into the eye of the Sage of Six Paths himself—the Rinnegan.
"What?!"
Shisui's pupils shrank in disbelief.
It sounded impossible.
He knew about the existence of the Eternal Mangekyo Sharingan. After Uchiha Kofū died, Shisui had read the clan's secret records, which contained information about their ancestor Uchiha Madara's eyes being just like this.
But the Rinnegan?
Shisui's mind immediately recalled the red-haired boy he had seen in Amegakure.
His eyes... evolved from the Sharingan? But isn't he from the Uzumaki Clan?
Also, the Eternal Mangekyo's power was so noble; did a power truly exist in this world that was equal to it in level and completely opposite in attribute?
"Wait…"
Uchiha Shisui felt a surge of doubt in his heart, seemingly realizing something, and suddenly gasped, "First Hokage, Senju Hashirama?"
The only one who could rival his ancestor was the First Hokage!
But wasn't the First Hokage long dead?
Forbidden experiments happened everywhere, but he never imagined that someone as revered as the First Hokage would suffer such a fate.
"A very precise guess. It's indeed the cells of the First Hokage, Senju Hashirama."
A smile appeared on Yoru's face. "I know you have many questions, but don't worry. We'll conduct the experiment, and everything will become clear."
"Remember, you must use your eyes' dōjutsu power to suppress the power of Hashirama's Cells. Otherwise, I'll have to forcefully move the experiment to phase three."
"Yukiko, prepare to begin."
"Yes, Yoru-sama."
Shisui's eyes widened as Yukiko calmly cut into his arm with a scalpel and removed a palm-sized piece of flesh.
He barely flinched, enduring the pain with a slight furrow of his brow.
Then Yukiko injected a pale, swirling solution into the exposed muscle—an experimental fusion agent.
Immediately, his arm's veins swelled grotesquely. Something was fermenting inside. A cold sweat broke out on Shisui's forehead.
It was painful—but still bearable.
Until—
The Hashirama cells were injected.
That's when everything went wrong.
Shisui's body convulsed violently. His muscles spasmed. His back arched off the table.
From the wound, fleshy growths burst forth—like live worms burrowing through his body.
"AAAAAAHHHH!!"
"Use your dōjutsu power to suppress Hashirama's Cells!" Yoru's voice boomed like thunder in Shisui's ears.
But the pain was overwhelming.
Shisui didn't even seem to hear. His limbs flailed uncontrollably, his eyes rolled back, and his entire consciousness teetered on collapse.
"It's no good, Yoru-sama!" Yukiko cried. "The fusion agent's barely working! The Hashirama cells are going berserk—his heart rate, blood pressure, cell activity—they're spiking fast! Ten more seconds like this and he'll either explode—or mutate into a tree!"
"Inject another dose—NOW!"
"Yes!"
Yukiko jammed a second fusion vial into his arm. Shisui jolted—but the grotesque changes barely slowed.
Yoru's voice dropped to a cold murmur.
"Just imagine it, Shisui... all your 'artwork'... your legacy... playing on loop in theaters across the entire shinobi world."
"Imagine the faces of the Uchiha, of Konoha—everyone—watching every moment you produced."
"A best-selling masterpiece, no doubt."
"A...aa…"
Those words finally elicited a slight sign of resistance from Shisui's body.
The power of his Eternal Mangekyo was slowly activated. The distorted state of his limbs began to slow, and the squirming tendrils seemed to gradually be suppressed, retracting little by little.
"Yoru-sama, cell activity is dropping! It's returning to normal levels!" Yukiko's excited voice rang out. The values displayed on the instruments confirmed that Shisui had suppressed Hashirama's Cells.
"Indeed, if even that hack Danzō could suppress them, there's no way you couldn't." Yoru let out a sigh of relief upon seeing this. "You are an Uchiha master whom even I acknowledge, comparable to the most proficient of teachers!"
Now that Shisui's Mangekyō was slowly assimilating the Hashirama cells, the experiment could move forward.
Now... comes the moment of truth.
Yoru leaned in, watching Shisui's eyes intently.
The change was subtle at first.
The intricate lines of the Eternal Mangekyō began to warp.
The black curves thickened, twisted. They began to overlap, becoming dense, tangled—a storm of chakra markings.
Chakra flooded to Shisui's head. His eyes were evolving again.
"It's happening…!"
This was the sign: the Sharingan's pattern distorting toward its final form.
From tomoe, to Mangekyō, to Eternal.
And from Eternal—to Rinnegan.
But then…
Something stalled.
The transformation slowed, then… stopped.
The lines faded.
The eye's pattern slowly returned to its original Eternal state.
"Damn…" Yoru's brow furrowed.
Does he need to experience something like Madara, a brush with death, to fully awaken the Rinnegan?
"Is… is it over…?"Uchiha Shisui, slowly regaining consciousness on the operating table, uttered a weak voice.
"Half a success," Yoru replied. "Do you feel any changes?"
"There doesn't seem to be any change... No, wait." Shisui frowned, sensing everything in his eyes. "Dōjutsu power has increased, greatly, but it doesn't seem to be the qualitative change you spoke of."
So, the evolution stopped midway.
Yoru tapped his fingers in thought.
"We'll let you recover for two days. Then we'll try again."
He turned to Yukiko.
"Prepare another Sharingan. This time… we'll implant it directly into the area where we added the Hashirama cells."
Just as Yukiko nodded—
"So... another experiment, huh?"
A childlike voice cut him off. A small figure stood in the doorway—a round-faced boy with piercing eyes.
"Yagura?" Yoru blinked, surprised. "You've adapted faster than I expected."
"More or less," Yagura said, gripping the hilt at his waist. "I think I've started hearing its name. I might be ready to… release my Zanpakutō."
"Really?"Yoru's eyes instantly showed extreme curiosity. Beside him, Kurushirare Kushimaru immediately removed his mask, staring wide-eyed at Yagura.
"Why can't I sense anything?!"
"How did you do it? What kind of power is that?"
"What kind of power, you ask..." Yagura murmured, pondering. "It's like having a heart-to-heart conversation with your closest, most intimate partner."
"I call out to it, it answers me, and everything falls into place..."
PS: Read Advance Chapters at https://www.patreon.com/c/ReadJin