[Reality Gem (Unique in the Universe): Cannot be embedded – Conditions Not Met. Cannot be removed once embedded.]
Kamui frowned as he stared at the glowing crimson stone suspended in the translucent interface. The system helpfully provided a brief description:
The Reality Stone first appeared in a Marvel universe. It allows the user to alter reality according to their will. If the wielder believes something is true, then it is. If they believe something is false, then it simply ceases to be—logic and objections be damned.
Kamui stared at it for a long while but couldn't figure out how to use it.
"…Screw it," he muttered. "I'll deal with it later."
He closed the interface and got back to preparing for war.
Back in his room, Kamui packed a basic ninja kit—kunai, shuriken, wire, smoke bombs—and strapped the pouch to his hip. He gathered water, rations, and sealed them into his newly acquired infinite storage space. His gaze fell on a standard-issue Uchiha short sword leaning against the wall. He picked it up, testing the balance, and headed toward the clan's gathering point.
As he walked through the compound, the somber atmosphere was almost suffocating. Everyone wore the same tense expression—grim eyes, tightened jawlines, faces hardened by the endless bloodshed of the Warring States era.
Kamui almost felt out of place.
"Kamui!"
A familiar voice called from behind. He turned to see Izuna approaching, fully geared up in light armor.
Kamui grinned and reached out to ruffle his younger cousin's hair.
"Hey, cut that out!" Izuna swatted his hand away, scowling.
Kamui just chuckled and did it again. "Don't worry. I can protect my little brother now."
Izuna didn't slap his hand away this time.
Before Kamui could say more, another voice called out from the distance.
"Kamui."
Madara walked toward them with his usual cold, commanding presence. Kamui quickly dropped his hand from Izuna's head, instinctively remembering Madara's infamous brother complex.
No point getting into a scrap over head-pats.
"We're hitting the Senju tonight," Madara said seriously. "You and Izuna stay close to me. Don't stray—understood?"
"Got it, Brother Ban."
Madara's eye twitched. Brother Ban? That was… new. He couldn't even remember what Kamui used to call him. Young Patriarch, maybe? Still, "Brother Ban" had a nice ring to it. He decided to allow it—for now.
Satisfied, Madara reached out to ruffle Izuna's hair himself. Kamui caught a glimmer of warmth in his cousin's expression before Madara quickly masked it with arrogance again.
The three of them arrived at the main square just as more Uchiha trickled in, forming into orderly units. Moments later, Uchiha Tajima emerged, standing before his clan with hands clasped behind his back.
He scanned their faces—warriors, children, parents, sons—wondering how many he would lose tonight. But he pushed the thoughts aside. There was no time for sentiment.
"For the glory of the Uchiha," he said simply.
No rousing speech. No dramatic farewell. Just cold, hard purpose.
The Uchiha force moved out.
As they marched, Kamui's mindset shifted. The tension in the air—the burning resolve in the eyes of the men and women around him—it began to stir something inside him. He glanced at Madara's back and Izuna beside him. The detachment he'd felt as a reincarnated outsider slowly began to fade.
This is my clan now. My family.
He opened his map and watched the red dots move. The Senju base wasn't far—just across a river. In the original timeline, it was the same river where Madara and Hashirama once skipped stones as boys. Now, it marked the border of a battlefield.
The squad halted at the river. Chakra flowed to their feet as they walked across the surface in silence—another reminder that in this era, tree walking and water walking were basic survival skills, not tricks taught to academy kids.
Once across, their pace slowed. Uchiha scouts began clearing traps—most were their own, set during past skirmishes—tripwires, explosive tags, and chakra-triggered alerts. The path to the Senju base slowly opened up.
"Enemy attack!"
The Senju garrison exploded into motion.
Inside the camp, Senju Xuanjian cursed. "Damn it! The clan leader's off supporting the Uzumaki—we're undermanned! Why the hell did he choose now?!"
Beside him stood a young boy, his hair half-black and half-white. He was visibly trembling.
"Itama!" Xuanjian barked. "Go get the clan head. Now!"
Senju Itama, youngest brother to Hashirama and Tobirama, nodded quickly. He turned and bolted from the compound, heading straight toward the forest.
Meanwhile, Kamui had gotten separated from Madara and Izuna during the charge. It didn't matter. With the power of the Flame-Flame Fruit, he was practically untouchable. His elemental body could shrug off most physical attacks—unless, of course, someone used sealing techniques.
So far, no one had.
Sword in hand, Kamui sliced through several traps and continued deeper into the woods.
That's when he met him.
Senju Itama.
A quick scan told Kamui this wasn't just some grunt. The tension in the boy's stance, the blade in his hand, the bloodline—this was someone important.
Kamui didn't hesitate.
"Uchiha Style: Flash Cut!"
A horizontal slash shot forward, chakra lacing the blade. Itama froze for half a second—just long enough to miss his chance to dodge. But at the last moment, he raised his sword and blocked.
The impact drove him back, but he didn't fall.
Not bad, Kamui thought. He's got instincts.
Their blades clashed again. Kamui pressed forward with fierce combos, his strikes enhanced by chakra. Itama parried every blow, his technique solid and grounded. He even managed a few counterattacks—though each one simply passed through Kamui's intangible form.
Still, Kamui's chakra reserves were draining fast. Fire-style techniques, swordplay, elemental transformation—it was a heavy load.
His breathing grew ragged. Damn. I can't keep this up…
Then—clang! Itama knocked the sword from Kamui's hand.
Kamui instinctively tried to shift into his elemental form—but nothing happened.
What!?
Panic surged through him. He'd let his guard down—and now the sealing technique on Itama's blade was interfering with his powers.
He couldn't dodge.
Itama's sword came down—
—and suddenly, something inside Kamui erupted.
A violent chakra surged toward his eyes. His vision sharpened. Time slowed.
In an instant, his black eyes bled into red.
One tomoe.Two.Three.
And then—Mangekyō Sharingan.
The system chimed.
[Reality Gem – Conditions met. Embedding now…]
A new power flooded Kamui's left eye, twisting the Mangekyō into a unique, spiraling design unlike any seen before.
Itama's blade came down——and vanished.
Literally.
One second it was there, the next, it simply faded from existence, disintegrating into red motes of light.
Itama stared at his now-empty hands. "What the—where's my sword?!"
Kamui stood up slowly, blinking as the world reoriented itself. The activation had been instinctive, like muscle memory—an ability triggered by danger and desperation.
Before either could speak again—
"Kamui! I'm here!"
Madara appeared through the trees, Izuna at his side.
Seeing the odds shift, Itama wisely turned and fled. But just before vanishing into the forest, he called back over his shoulder:
"Uchiha Kamui… next time, I'll defeat you!"
Kamui opened his mouth to respond—but the boy was already gone.
He let out a breath he hadn't realized he was holding and stared down at his own hands.
Mangekyō Sharingan.
Reality Gem embedded.
This world just got a lot more interesting.