The illusion cast by the Sharingan is fundamentally different from standard Genjutsu. Its core lies in the eye itself—no hand seals are necessary. One only needs to make eye contact with the opponent, and the illusion takes effect.
In the original book, only a few individuals mastered this ocular Genjutsu to its peak. Among them, two stood out prominently: Uchiha Madara and Uchiha Itachi.
Itachi's mastery of Genjutsu was unparalleled. Even compared to Shisui Uchiha—whose Mangekyō Sharingan possessed the fearsome Kotoamatsukami, a technique that could manipulate the will of others without them realizing it—Itachi's illusions were terrifying. His use of Tsukuyomi, an instantaneous Genjutsu that warped the victim's perception of time, was a technique feared even among the most elite shinobi.
Madara Uchiha, meanwhile, showcased the overwhelming power of the Sharingan during the Fourth Great Ninja War. Armed with his Eternal Mangekyō Sharingan and later the Rinnegan, Madara single-handedly overwhelmed the Allied Shinobi Forces. His mastery of Genjutsu, paired with taijutsu and ninjutsu, allowed him to subdue multiple opponents with just a glance. Shinobi who looked into his eyes were rendered paralyzed, unable to resist as he carved through them with ruthless precision.
Though Uchiha Kai may not have reached the heights of these two legends, his Genjutsu skills were nonetheless formidable.
With a mere flicker of mental will, Uchiha Kai activated his Genjutsu. Just as Kuri lunged at him, Kuri's mind was thrown into a sudden and fatal disorientation.
Seizing the opportunity, Kai mirrored a maneuver reminiscent of how Itachi once caught Sasuke's Chidori—he grabbed Kuri's chakra-charged arm with unshakable grip and slammed it toward the ground. At the same time, Kai's chakra-infused ninja blade arced downward, aiming for Kuri's head.
Kuri, however, demonstrated the tenacity expected of a seasoned shinobi. Despite being caught in the illusion and restrained, he managed to regain focus in a fraction of a second. Though his right arm was pinned, he still had his left.
Without hesitation, a blinding surge of chakra erupted from Kuri's left hand. He unleashed a desperate counterattack, punching toward Kai's chest in a suicidal charge.
It's a universal truth among shinobi—when backed into a corner, they will risk everything for a chance to survive.
Kai anticipated the move and was forced to release Kuri's arm, retreating swiftly. He was unwilling to die a meaningless death with his mission incomplete.
But Kai was no pacifist. Though forced to withdraw, he retaliated. As Kuri's left hand surged forward, brimming with explosive chakra, Kai's blade slashed cleanly across it and was quickly abandoned mid-swing—sacrificing the weapon to avoid a direct explosion.
"Boom!"
The thunderous detonation from Kuri's explosive-style jutsu sent dust and rubble into the air. Kai leapt back to create distance, ears ringing from the blast.
As the dust cleared, Kai spotted Kuri staggering to his feet and trying to flee.
"Trying to run?" Kai sneered. He immediately drew a kunai and gave chase.
For Kai, the battlefield was as clear as day. His Sharingan allowed him to perceive chakra flow, anticipate movement, and detect even the subtlest muscle twitch.
Kuri, wounded and weary, cursed under his breath. He had grossly underestimated the power of the Uchiha—and the terror of the Sharingan. This boy—barely thirteen or fourteen—possessed a fully awakened Three-Tomoe Sharingan, and it was no bluff.
He had fought Uchiha before, both awakened and unawakened. None had troubled him—until now. He had always believed the clan's reputation was exaggerated, little more than myth.
He had tried to avoid Kai's gaze, kept his rhythm unpredictable. But even the briefest lapse gave Kai an opening—and in that fraction of a second, he had been caught by a Genjutsu. No hand seals. No visible signs. Just eye contact. And it nearly cost him his life.
Though he escaped with his life, he had lost his left hand in the exchange.
Now he was bleeding out. His vision blurred, his thoughts scrambled. If he didn't stop the bleeding soon, he'd be dead. But if he turned his back on Kai, he'd be killed anyway.
"Damn it! So fast—?"
Suddenly, Kuri felt a chilling presence behind him.
Too late.
A kunai pierced straight through his back, directly into his heart.
Kuri's eyes widened in shock. His body froze. Then, he collapsed face-first into the earth.
Behind him, Uchiha Kai tilted his head slightly, a faint smirk on his lips. His eyes, still glowing red, showed not a shred of pity.
"Is that all? Compared to Kitsuchi of Iwagakure, you're nothing."
Kai's voice was calm, almost mocking.
But just then, a new chakra signature flared—exploding from the rubble behind!
"What—?"
Kai's expression shifted. Another attacker was charging him with a massive chakra buildup.
Kuri had created a diversion. It was a shadow clone that had died—Kai had fallen for it.
But he recovered instantly. The punch passed through his afterimage—another clone.
Kuri, relentless despite his injuries, spun around, gathering chakra for a final attack. Blood spilled from his severed limb, yet he swung with inhuman willpower.
Thirty centimeters. Ten centimeters—
Just before the punch landed, Kai twisted his body gracefully, dodging by a hair's breadth. At the same moment, his kunai drove deep into Kuri's chest.
The weapon buried itself up to the hilt, piercing through Kuri's ribs. Blood poured from the wound, soaking the ground beneath them.
"Did you really think I couldn't see through you?" Kai's voice was ice-cold. "With these eyes... there's nothing you can hide."
And with that, Kai twisted the kunai sharply.
A scream tore through the battlefield, echoing across the empty plains.