At the Demon Slayer Corps headquarters, the main hall was dim. The curtains were half drawn, and faint beams of sunlight spilled through the gaps, falling on the tatami floor but unable to drive away the heavy air inside.
Ubuyashiki Kagaya lay on a low futon covered with thick quilts. His face, already pale, now looked ashen, and his breathing was so shallow it was barely audible. The curse had spread to his chest— even sitting up had become a luxury.
By his side sat Ubuyashiki Amane, holding a warm towel as she gently wiped his forehead. Her eyes were full of pain, but she said nothing to stop him—she knew her husband carried the weight of the entire Corps, the mission to destroy Kibutsuji Muzan. Even if only one breath remained, he would never stop.
Tamayo entered quietly, carrying a wooden medicine box. She wore a plain kimono, her face showing exhaustion, yet her eyes glimmered faintly with determination.
Setting the box on the tatami, she opened it carefully. Inside were three glass vials, each clear and shining with a subtle glow beneath the sunlight. The vials were labeled red, blue, and green.
"Kagaya-sama," Tamayo said softly, her tone gentle but steady. "The medicines are finally complete—enough to help us kill Muzan."
Kagaya's dim eyes brightened a little. He turned his head with effort, looking toward the vials. His voice came out weak and hoarse. "You've worked hard, Tamayo-san. These three… what does each one do?"
Amane helped him sit up slightly, supporting his shoulders and offering him a cup of warm water.
Tamayo lifted the red-labeled vial. "This one is the Humanization Agent. It completely destroys the Muzan cells inside a demon's body, reverting them back into a human."
Then she picked up the blue-labeled vial. "This is the Aging Agent. It accelerates the degeneration of Muzan's cells, drastically reducing his regeneration ability. He'll even temporarily lose access to his Blood Demon Art. The effect lasts for one hour—enough time for us to stall until sunrise."
Finally, she held up the green-labeled vial. "This is the Inhibitor. Once injected, it completely locks the regenerative function of Muzan's cells. Even if any remain, they can no longer divide or grow. Once he's exposed to sunlight, he'll be burned away completely."
Tamayo placed the vials back neatly into the box. Her voice grew firm. "If we inject these three medicines into Muzan in sequence and manage to drag the battle until dawn, we can kill him completely. This is the most reliable plan we have."
Kagaya smiled faintly, a flicker of relief crossing his face. But soon his expression darkened again as he looked back to Tamayo. "What about Giyu and Obanai? They're still Upper Moons. Can we use the Humanization Agent on them first? They're our comrades—we can't let them fight under the guise of demons forever."
Amane paused, hope flickering in her eyes. She still remembered Giyu when he first joined the Corps—quiet but earnest, always protecting his teammates without complaint. And Obanai—cold on the surface, but more loyal than anyone when it came to his comrades.
But Tamayo slowly shook her head, her gaze tinged with regret. "Not yet, Kagaya-sama. You understand how tightly Muzan controls his Blood Demon Art, especially over the Upper Moons. If we revert Giyu and Obanai now, Muzan will sense it immediately. He'll realize we have a serum capable of reversing demonization—and once he knows that, he'll grow cautious. He may go into hiding entirely and never show himself again."
She continued, voice calm but heavy. "Right now, Giyu and Obanai's status as Upper Moons is our greatest disguise. They can spy within Infinity Castle, relay Muzan's movements, its structure, and when the battle begins, they can disrupt the Upper Moons from within. If we bring them back now, we lose our two most valuable pieces—and the odds of victory will drop sharply."
Kagaya fell silent. He knew Tamayo was right. But the thought of Giyu and Obanai still enduring Muzan's control, fighting their inner struggle every moment—it weighed on his heart.
Amane gently took his hand, silently comforting him.
After a long pause, Kagaya finally spoke again, his tone resolute. "I understand. We'll proceed according to your plan. Those two… will have to bear this burden a little longer."
He looked toward Tamayo, his eyes steady. "Amane, call back all the Hashira—and Tanjiro and Tō as well. There's something I must announce."
Tamayo blinked in surprise, then understood immediately—Kagaya could feel that his time was running short. He wanted to lay out the final battle plan himself.
She bowed her head. "I'll arrange it right away."
…
The next day, the main hall was filled. The Hashira sat in rows; Tanjiro, Himejima, and Shinazugawa sat at the front. Each face was solemn.
Kagaya lay on the futon. Though his body remained weak, his gaze was sharp as it swept across the room.
"Everyone," his voice was soft but carried clearly through the hall, "I know you've all been preparing for the final battle. But I fear… I may not live to see our victory."
The room fell silent.
Tanjiro's mouth opened as if to speak, but Kagaya lifted a trembling hand, signaling for silence.
"This isn't something to mourn," he said with a faint smile. "The Ubuyashiki family has carried this mission for generations—to stand against Muzan. To die seeing hope for his destruction… is enough for me. Today, I've gathered you all to finalize the battle plan."
He turned his head slightly toward Tamayo, giving her a small nod.
Tamayo rose, carrying the box to the center of the room. Once again, she explained the function of the three vials. Then she spoke clearly, her words steady.
"The core of the plan is three steps—lure, inject, delay.
Step one: Lure. We must draw Muzan out of Infinity Castle. The best bait would be something that truly interests him—such as… a false report about the Blue Spider Lily."
"I'll be the bait!"
Kamado Tanjiro stood up at once, his eyes burning with resolve. "Muzan has always wanted to kill me. If I expose my location on purpose, he'll definitely come out!"
Ubuyashiki Kagaya gave a small nod. "Then I'll leave the task of luring Muzan to you, Tanjiro."
He turned his weak gaze toward Shinazugawa Sanemi and Uzui Tengen. "Sanemi, Tengen—you'll be responsible for restraining Muzan's Blood Demon Art. Sanemi, your Wind Breathing can disrupt his attack rhythm. Tengen, your rhythm-based perception can predict his movements. You two must create an opening for those who will administer the medicines."
"No problem!"
Both men answered in unison, eyes sharp with fighting spirit.
"Kanroji, Shinobu," Kagaya continued, looking toward the two sisters, "you will work with Tamayo-san to administer the injections. Kanroji's Flower Breathing can provide wide-area control, and Shinobu's Insect Breathing offers precise strikes. You must coordinate perfectly to ensure all three vials are successfully injected into Muzan."
Kanroji and Shinobu exchanged a glance, then nodded firmly. "Understood."
"Finally…" Kagaya's gaze softened as he mentioned the names not present. "Giyu and Obanai will act within Infinity Castle, disrupting the other demons and preventing reinforcements from reaching Muzan. The Kakushi will stay in contact with them and relay any vital intelligence immediately."
After issuing all the orders, Kagaya's breathing grew ragged. Amane quickly brought him a cup of warm water. He sipped, then continued speaking with effort. "The battle will begin in three days. During these three days, everyone must complete their final preparations.
—The Kakushi will finish compiling the maps of Infinity Castle and distribute them to all.
—Tamayo-san will prepare additional support serums—coagulants, antidotes, and healing tonics.
—Each Hashira must focus on mastering their Demon Slayer Marks, ensuring they can fight at their full power when the time comes."
He paused, his gaze moving slowly across every face in the room. His tone deepened with solemn strength. "I know the final battle will be brutal. The cost will be high. But I believe in you all. As long as we fight together—as long as we remember those who were lost to demons—there's no doubt in my mind that we can win."
"For those who will never return, for a world without demons…"
His voice grew faint, but the conviction in it never wavered. "By the name of the Ubuyashiki family, I entrust everything to you."
Everyone in the hall rose to their feet. They bowed deeply in unison, their voices echoing with unwavering resolve: "We will not fail!"
Tanjiro tightened his grip around his Nichirin Sword, the orange-red blade gleaming coldly in the light. He thought of his family—of Giyu—and made his silent vow: he would kill Muzan, no matter the cost, so that everyone could live in peace again.
Tō ran his fingers over his empty left sleeve, his expression set with fierce determination. He would avenge Rengoku Kyojuro. He would free Giyu from Muzan's control. He would make the name of Storm Breathing blaze brightly in the final battle.
Agatsuma Zenitsu and Hashibira Inosuke also gripped their swords tightly. One still trembled from fear, the other burned with reckless energy—but this time, both carried an unshakable resolve.
They were no longer boys trailing behind Tanjiro. They were warriors of the Corps—ready to stake their lives on victory.
After the meeting ended, everyone dispersed from the main hall to begin their work.
The Kakushi moved swiftly through headquarters, relaying orders and preparing supplies. Tamayo and Shinobu returned to the laboratory to mass-produce the support serums. The Hashira went back to the training grounds for their final drills. The glow of Demon Slayer Marks flared one after another across the courtyard, illuminating the night.
Inside the main hall, Kagaya leaned against Amane's shoulder, watching the busy figures outside with a faint, peaceful smile. He knew his time was running out—but he had already done everything he could to prepare them. The rest would be up to these young warriors.
"Amane," he murmured quietly, "after this battle is won, take the children somewhere peaceful—somewhere with flowers. Live a quiet life. Forget the mission of the Ubuyashiki family. Just be their mother. Watch them grow."
Amane's tears finally spilled down her cheeks as she nodded gently. She understood. She always did.
He had already decided to act as bait himself. The plan he had just laid out was only to conceal that truth—because no one in the Corps would ever allow their master to be the one to risk his life first.
Her voice trembled as she whispered, "I will. I'll tell our children… that their father was a great hero."
Sunlight streamed through the window, warm and soft as it fell upon the two of them.
Though the shadow of battle still loomed over them all, the Demon Slayer Corps headquarters now brimmed with quiet hope.
Everyone knew that what awaited them was a fight between life and death—but they also knew that as long as they stood united, there was no darkness they could not overcome.
Three days from now, at dawn, the fate of humans and demons would be decided.
And every heartbeat, every breath from this moment on, was a step closer to that final battle.