The world went silent. In the sterile, unending space of the Infinity Castle, Tamayo's mind went blank. She couldn't process what had just happened. She had gambled everything on Muzan consuming her and the potent anti-demon drug she had developed. It was her final, desperate plan, the culmination of centuries of hatred and research. But she never imagined that after all this time, he had never trusted her for a single second.
What truly broke her was the realization that Muzan hadn't just anticipated her plan—he had controlled it. Her every move within the fortress had been watched. For every step she took, he had prepared a perfect countermeasure, turning her own strategy against her with horrifying precision. He had created two identical replicas, perfect copies that allowed him to manipulate the situation from the shadows.
But the most crushing truth was that the entire process of creating the medicine had been under his complete control from the very beginning. From the moment he brought her into the Infinity Castle, her fate was sealed. Both she and Nezuko Kamado had served their purpose. Their value had been completely extracted, whether they wanted to believe it or not.
"Did you truly think it would be that simple, Tamayo?"
Muzan's voice was a cold, cutting whisper that sliced through the silence. He looked down at her dazed expression with utter indifference, his crimson eyes holding no warmth. Her centuries of planning, her ultimate sacrifice—it was nothing more than a trivial game to him, a simple puzzle he had solved long ago. To him, her desperate scheme was just a low-level maneuver, hardly worth a second thought.
But for Tamayo, that maneuver was her entire world. Its failure was a blow that shattered her psychological defenses. The only reason she had endured this long, the only reason she hadn't given up, was the hope of finally achieving her revenge. She clung to that hope, that burning desire to see the demon progenitor destroyed.
Now, facing this monstrously intelligent being who had played her like a puppet, Tamayo understood the futility of it all. Any action she could take would be meaningless. A terrifying thought clawed at her mind: with things as they were, even taking her own life was no longer an option.
"Ugh…"
A strangled gasp escaped her lips as the world began to warp. The stillness was broken, and a look of pure agony twisted her features.
"It seems the other medicine is taking effect," Muzan noted, his tone chillingly calm. "The one you injected into yourself."
A strange buzzing filled her ears. The moment he finished speaking, a horrifying change began. Wrinkles spread across her delicate face like cracks in porcelain. Her beautiful, lustrous black hair lost its sheen, turning a brittle grey and seeming to crumble into dust before her very eyes. In just a few seconds, the visage of a woman in her prime had vanished, replaced by the withered face of a shrunken old woman.
She could feel it happening inside her. The power that had sustained her for centuries, the very cells of Kibutsuji Muzan that she had fought to control, were being destroyed at an incredible rate. The drug she had taken—the self-aging compound meant to cripple him from within—was now her own executioner. She had hoped to use it to weaken him when he consumed her, but her plans had crumbled to ash. Now, she was the one tasting the bitter poison.
Her breathing grew shallow, and she could feel her own heartbeat slowing, each pulse weaker than the last. An indescribable sadness washed over her, a grief so profound it felt like drowning. She had imagined her death a thousand times over the centuries, but she had never envisioned it being this pathetic, this tragic. To have the will to destroy demons, but to be left with no power to change her own fate.
"Tamayo, can you feel it?" Muzan's voice seemed to come from a great distance, echoing in her ears. "Can you feel death approaching?"
His face began to blur, his features becoming indistinct. The dose of the aging drug she had injected was massive, and combined with the human-transformation medicine she had also developed, the effect was catastrophic. The only reason she hadn't turned to dust already was that the chemicals needed a few moments to fully permeate her body.
But those few seconds stretched into an eternity. Her senses began to fail. Sight, hearing, touch—everything slowed down, becoming muted and distant.
So this was death.
The air in the Infinity Castle grew thick and still once more, the eerie quiet broken only by the muffled shrieks of Nezuko, who was still suspended helplessly in the air. Her struggles were useless; her demonic power was nothing before the might of the demon progenitor.
Muzan glanced at the dying woman on the floor, his eyes sharp and analytical. He remembered the original course of events, the future he had worked so hard to change. In the final battle of that timeline, Tamayo's medical genius had nearly been his undoing, weakening him so severely that the Demon Slayer Corps stood a chance. Even then, he had been strong enough to fight the remaining Hashira to a standstill. It was a testament to his overwhelming power.
But that future would never come to pass. Tamayo's death, while perhaps a shame, was a necessary step in his plan. It had always been part of his calculations. After all, if she didn't die, then he and his ambitions would.
He stared down at her with something that almost resembled pity, but was merely cold observation. "You chased this foolish dream of revenge for centuries, clinging to hope like a child. And this is where it ends. Not with a heroic sacrifice, but with a quiet, pathetic whimper. Your life, your rebellion… it was all meaningless."
His gaze shifted from her withering form to Nezuko. "Now, it's your turn. You're quite the variable, aren't you?" A cruel smile touched his lips. "Your brother is so desperate to kill demons. I think it's only fitting that you, his precious demon sister, will be the one to end him for me."
With a casual motion, he reached out. The Tamayo replica standing silently behind him held out a small vial—the true medicine, the one that granted immunity to the sun. He took it without hesitation and swallowed its contents in a single gulp.
"And now," he declared, his voice resonating with newfound power, "all of this comes to an end."
The moment the words left his lips, a terrifying power erupted from within him. The very air in the Infinity Castle warped and screamed as his energy surged outwards in every direction. A thousand-year-old dream was no longer a dream. The perfect being, the ultimate creature that Kibutsuji Muzan had always strived to become, was finally about to be born.
It was a pity. The woman who had dedicated her entire existence to seeing him destroyed would not live to witness his ultimate triumph.
An immense pressure radiated from Muzan as the center of a storm. He could feel it—the power in his veins reaching a critical point, a threshold he had never crossed before.
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