According to Mahoraga's analysis, there were two ways to completely kill the Sage of Six Paths. The first was to destroy the entire ninja world, which would nullify his immortality. The second was to separate the authority of the ninja world from his body, which would also make him mortal again. Kagami naturally wouldn't choose the first option; he still wanted to unify the world. Therefore, he had to choose the second.
Mahoraga had already provided a solution: Yamato, the sword with the ability to separate everything. However, simply using the sword wasn't enough. Kagami would have to merge with it and use its most powerful attack to sever the connection between the Sage and the authority of the ninja world.
Without hesitation, Kagami took out Yamato and stabbed it directly into his own heart. A crisp sound echoed as the blade sank into his chest. Black demonic energy emanated from his body. Because he had the blood of a devil, Yamato resonated with him. Instead of dying, he began to absorb its power.
But Yamato's power alone was not enough. To separate the Sage from the authority of the ninja world, he had to increase his strength to its absolute peak. He took out the Rebellion and the Sparda swords and stabbed them into his chest as well. As the power of the three demonic blades merged with him, his aura surged to an unprecedented level. He could no longer maintain his human form. A pair of huge demon wings grew from his back, and a red and blue light enveloped his body. His eyes turned scarlet, filled with a cold, murderous intent. He had become a true demon, the form Dante and Vergil took after fusing with the Sparda sword. And because he had also integrated the power of Yamato and Rebellion, his current strength surpassed theirs.
"Sage of Six Paths," a sinister smile appeared on his lips, "this time, you are dead."
He waved his hand, stopping the Gatling Bodhisattva's attack. The monster transformed by the Sage quickly returned to its original state, but it had already lost its mind, driven only by the desire to kill. It roared and rushed toward Kagami again.
"Fool," Kagami said, flapping his wings and flying into the air. A huge demon shadow, a projection of himself, appeared behind him, exuding an extremely terrifying aura. The shadow drew a huge sword, condensed from the power of Yamato.
As Kagami and the Sage met, the demonic shadow slashed out. A scarlet blade light, hundreds of meters long, swallowed the Sage, cutting him in half. This time, his body did not recover. Instead, it began to twist. The connection between him and the authority of the ninja world had been severed. He could no longer control its power.
Countless souls emerged from his body and flew to various parts of the ninja world—the souls he had previously devoured. His body began to collapse, and his soul became unstable. The effect of Yamato's blade also woke him from his madness. Seeing his power gradually being lost, his face filled with resentment. "You damned human!" he roared at Kagami. "What have you done to me? I am the immortal and indestructible true god of the ninja world!"
"A piece of trash like you is worthy of being called a god?" Kagami sneered and slashed again. The authority of the ninja world was completely separated from the Sage's body.
"No, I won't accept this!" the Sage roared, his voice echoing throughout the space. "I've finally become the only true god in this world! How could I possibly die here? Kagami, it's all your fault!" But no matter how he roared, he could not stop his body from dissipating. His soul completely disintegrated in unwillingness and despair. The man who had dreamed of ruling the ninja world was finally gone.
The authority of the ninja world transformed into a ball of light, quietly floating in the air, emitting a soft glow.