The air in the small, damp cave was thick with ozone, the sharp anxiety of the young Shinobi, and the metallic scent of old blood. It was 26 FE, the tenth and final year of the First Shinobi War. Kagami, 32 years old and Tobirama's shadow, felt the chaos of the Kinkaku Force—two walking, Kyūbi-fueled berserkers—like a ticking clock in his gut.
Tobirama Senju, physically unharmed but spiritually exhausted, rose. He looked at his young proteges with the gaze of an engineer performing the final, bitter calculations for a structure whose completion required his own demise.
"The Kinkaku Force will not let us leave," Tobirama stated. His voice was not a battle cry, but a cold, incorruptible instruction. "One must serve as bait. A lethal, inescapable sacrifice to secure your escape."
He pulled out a parchment sealed in wax and handed it to Kagami. "This contains my final instruction for the Hokage succession and the consolidation of the System."
Kagami held the parchment. He felt the dual truth of the seal, the entire Konoha ideology, in his palm: outwardly, the official plan; inwardly, the secret order mandating Tobirama's own sacrifice and the immediate appointment of Hiruzen. Tobirama had taught the System that required sacrifice, but he had not perfected it. The System needed the death of its founder to survive.
Tobirama looked directly at Kagami. In that look, there was no warmth, only the ice-cold confirmation of their shared logic. It was the silent acknowledgment that only the two of them understood that this death was the most necessary of all. He did not say: I die for you. He said: The System requires swift generational change; stagnation is corruption. I am the bottleneck.
"I will play the bait," Tobirama declared. Danzo protested the loudest, a mixture of ambition and genuine shock at the loss of power. Hiruzen remained silent, his face contorted by pain and honor.
"Hiruzen," Tobirama said, his voice cutting through the protest. "As of today, you are the Second Hokage. Your mission is unity."
Kagami's silence was absolute. He did not move. He knew Danzo's anger and Hiruzen's grief were human, predictable reactions. But his own reaction was that of the System: the final, the highest payment was due.
Tobirama stepped out of the cave. Kagami heard Danzo's gasping breath, Hiruzen's quiet sob. He himself felt nothing. Only an unbearable, steely emptiness where the entire ideology was centered. He did not wait for the fight. He waited for the erasure.
Then it came: A massive, chaotic burst of Chakra outside the cave, followed by a distorted, deafening silence. Tobirama's volatile Chakra, the anchor mark of his existence, was torn away.
Kagami fell to his knee, yet not from grief, but from the unbearable loneliness of control. The shock hit him not through the heart, but through the mind. With Tobirama's death, the last witness to the truth died, the only person who had shared Kagami's convictions and approved of his actions. The structure of peace they had built together was now utterly isolated within Kagami's head.
The weight of the final, sole truth rested now on Kagami alone. He was the only one who knew that Hiruzen was an illusion that had to be constructed. The uncomfortable logic of sacrifice had wiped out the architect.
At this moment of total, insurmountable logical necessity, Kagami's inner mirror shattered. The already active Sharingan convulsed. The three tomoe merged, twisted into each other, and opened into a Mangekyō pattern—a geometrically precise, spiral sealing matrix.
The Mangekyō had awakened: Gensō no Saihen (The Reconstruction of the Illusion).
The ability shot out into the damp air of the cave without his conscious volition, triggered by the cold command of his brain: "The gap must be sealed."
Kagami watched as the perceptions of his remaining comrades immediately realigned. It was the first, critical rewrite of Konoha's history. He used the Mangekyō to smooth over the memory of Danzo's hesitation and Hiruzen's moment of shock. Suddenly, Hiruzen remembered grasping Tobirama's hand and swearing to uphold his legacy, while Danzo had sullenly held back. The uncertainty gave way to a firm, heroic memory. Kagami had reconstructed the psychological hierarchy of the new Konoha in an instant.
They recovered Tobirama's body. Kagami used his Mangekyō one last time to shape the expression of the dead man. The pain and calculation gave way to an expression of peaceful, honorable acceptance. The mentor's final gesture was an illusion that provided comfort and generated loyalty among the survivors.
Kagami looked into a puddle collected on the cave floor. He stared into this wet, dark mirror. His reflection was there, but it was different. The eyes glowed with the unholy geometry of his new Dōjutsu.
He was the only one whose memory of Tobirama's actual orders and death remained unchanged. He was the loneliest man in Konoha.
The last thought of Uchiha Kagami died at that moment. Only the Architect remained, with a single, unwavering mandate.
"When the truth dies, only order remains."