"Giyu, wake up."
That familiar voice drifted to his ears, gentle as the summer breeze of his childhood nights.
Tomioka Giyu's eyes flew open—but there was no darkness of the Infinity Castle, no stabbing pain in his body.
He stood instead in the courtyard of his old family home. Sunlight filtered through the gaps in the cherry blossoms, falling softly over his sister, Tomioka Tsutako.
Tsutako wore a pale blue kimono, her hair tied simply at the back. She held a freshly picked plum in her hand and smiled as she handed it to him.
"Why did you fall asleep under the tree again? Here, try this. The plums are sweeter than last year."
Giyu froze. He reached out, taking the fruit from her hand. The cool skin brushed his fingertips, and the familiar texture made his eyes sting.
This was the summer when he was twelve. His sister was still alive. He hadn't joined the Demon Slayer Corps yet—hadn't known what loss truly meant.
"Aneue…"
His voice was hoarse, trembling as he spoke, almost afraid to believe what he saw.
"Silly boy, why are you crying?"
Tsutako reached out and wiped his tears away. Her touch was warm—real.
"Did you tire yourself out training again? Rest a bit. You don't always have to push yourself so hard."
Looking at her face, memories flooded back—his sister mending his torn practice clothes, waiting on the riverbank while he learned to swim, secretly praying for him at the temple and bringing home a charm.
Moments he had buried deep for years surfaced vividly before him now.
"Aneue, I…"
Giyu opened his mouth. He wanted to say he had become a demon, that there was no going back. But Tsutako gently interrupted.
"I know things are hard for you right now."
Her gaze turned serious.
"You met a powerful enemy. You became what you hate most. And now you think you're beyond saving, don't you?"
Giyu's head shot up, his eyes wide in shock—how could she know?
"Because I've been watching you all this time."
Tsutako smiled softly.
"I watched you join the Demon Slayer Corps, watched you become the Water Hashira, watched you meet so many comrades, watched you fight so hard to protect everyone."
"Giyu, you've never been alone. There are so many people who believe in you—they're all waiting for you to come back."
"Don't give up, Giyu."
Her voice grew firm.
"You're not someone who gives in easily, and you're not the kind of demon who loses himself and hurts others. Your resolve, your faith—they're still inside you. As long as you reach for them, you can take them back."
"Sensei! Don't give up!"
"Giyu-san, you promised to teach me the proper Hinokami Kagura!"
"Tomioka-san, you promised to spend next Tanabata with us!"
Tō's voice, Tanjiro's voice, Shinobu's voice—echoed together, distant yet strikingly clear.
They intertwined like beams of light, piercing through the darkness of his fading consciousness.
Yes… how could he give up now?
He remembered the moment Kokushibo had defeated him—when the demon had crouched before him, asking if he wanted to become one of them.
He hadn't even hesitated. "I will never become a demon!"
He had tried to grab his fallen Nichirin Sword, determined to fight one last time—but Kokushibo's blade had cut him cleanly in half.
As the pain exploded through his body, he caught the look in Kokushibo's eyes—a flash of regret—and heard him murmur, "What a pity."
Then everything went dark.
He didn't know how long he was unconscious, nor what had happened after. Only that when he woke again, he was being dragged through the endless corridors of the Infinity Castle.
He couldn't move, couldn't resist.
And when he was finally brought before Kibutsuji Muzan, cold blood poured into his veins—his body frozen, his mind drowning—until his awareness began to return like a tide creeping in from the abyss.
Inside the great hall of the Infinity Castle, Kibutsuji Muzan floated at the center. His crimson eyes were cold and lifeless as he stared down at Giyu. Kokushibo stood beside him, all six of his eyes filled with faint anticipation.
"Kokushibo recommends you to take the seat of the new Upper Moon Six. I'll give you one chance."
Muzan's voice carried no warmth. Black blood dripped from his fingertip and merged into Giyu's body.
"Drink my blood, and you will gain greater power. But remember—from this moment on, your life belongs to me. If you dare to betray me, I will make your existence worse than death."
As the black blood flowed through him, pain ripped through every vein, like countless blades slicing his organs apart. Yet within that agony surged a terrifying strength, mending his bisected body with unnatural precision.
He tried to resist, but his body refused to obey. All he could do was endure as that demonic energy reshaped him completely.
"Your mission is to join the other Upper Moons. Find the Blue Spider Lily and eliminate the Hashira of the Demon Slayer Corps."
Muzan's voice echoed coldly.
"Do not disappoint me, Upper Moon Six."
With a wave of his hand, he dismissed him.
Kokushibo glanced sideways at him and said calmly, "Get used to your new body. Don't waste Muzan-sama's blood."
"Upper Moon Six—Tomioka Giyu."
Giyu staggered as he left the grand hall, wandering down the endless corridors of the Infinity Castle until he came upon a patch of reflective water on the wall—a natural mirror formed from the condensation pooling on the surface.
He froze.
His reflection stared back at him, utterly changed.
His eyes had transformed—black sclera, irises etched with the words "Upper Moon Six." From his forehead grew a pair of curved black horns, faintly rippled with water-like patterns. Along his cheeks, deep blue lines resembling flowing streams ran from the corners of his eyes to his jaw, just like the markings of his Water Breathing.
Those markings… a Demon Slayer Mark?
Giyu reached up and touched his face. The skin felt cool, almost icy.
He had never managed to awaken his mark before, yet now, as a demon, it had appeared effortlessly.
But none of that mattered now.
He stared into the water mirror—at the horns, the eyes, the markings. Every feature screamed the same truth.
He had become a demon.
"Aneue…"
He whispered softly.
Images flashed in his mind—his sister's death that winter night, her throat torn open by a demon as she shielded him. Her last words still echoed in his memory: "Giyu, become a strong swordsman. Protect others. Don't end up like me…"
His sister had died by a demon's hands.
And now, he was one of them.
Agony and guilt tore through him. He dropped to his knees, clutching his head, a muffled cry breaking from his throat.
He couldn't accept it. He couldn't be one of the monsters that preyed on humans. He couldn't betray his sister's last wish, or the trust of Shinobu, Tō, and Tanjiro.
"I can't… I can't be a demon…"
He repeated it again and again. His nails dug deep into his palms, but he felt no pain—his new body too strong, too detached from human sensation.
Footsteps echoed at the end of the corridor. Giyu's head snapped up, eyes flashing warily.
He was a demon now—the enemy of the Demon Slayer Corps. But his heart still held a human's resolve.
He had to control himself. He couldn't lose his mind. He couldn't harm the innocent. If fate had turned him into a demon, then he would use that power for his own purpose—
Just like Tamayo-san.
Giyu rose slowly, gripping his Nichirin Sword tightly.
Even as a demon, he would not abandon his beliefs. He would still fulfill his sister's wish. He would still stand beside his comrades to destroy Muzan.
In the mirror of water, his demon eyes glowed a deep, stormy blue—but beneath that light, the unyielding will of a human still burned.