On the seventh day of Giyu's disappearance, the air at the Demon Slayer Corps headquarters was so heavy that it hurt to breathe.
The Kakushi had searched through every part of Kirigakure Village and the surrounding mountains. All they brought back was a patch of dried black-red blood, several shattered pieces of a Nichirin Sword, and a deep-blue haori torn cleanly in half—the haori that belonged to Tomioka Giyu. The edge still carried the faint scent of the herbs he always used.
"How is it? Are the test results ready?"
Kocho Kanae stood at the doorway of the Butterfly Mansion's laboratory, her voice trembling ever so slightly.
Behind her, Tō and Kamado Tanjiro stood with their heads lowered, hands clenched so tightly that their nails dug into their palms.
For seven days straight, they had joined every search mission. Yet they hadn't found even a shadow of Giyu.
Tamayo stepped out of the lab, her expression heavy as she shook her head. "The blood sample comparison confirms it—it belongs to Tomioka-san. The blood loss is massive, far beyond what a human could survive. And…"
She paused before continuing quietly. "On the Nichirin fragments, alongside his blood, there was another kind—black blood. It's from a demon."
Yushiro, standing beside her, added, "There were no traces of a body at the scene. Judging by the residual demonic aura, Tomioka-san was most likely devoured by the demon. Not even a corpse was left behind."
"Devoured…?"
Tanjiro's voice broke. His throat closed, and tears streamed down his face uncontrollably.
He remembered how Giyu had corrected his breathing posture, how he brought dorayaki for his siblings, how he quietly said, "I'll protect you all." Each memory stabbed at his chest like a knife.
Tō swayed on his feet, his face pale as paper.
He bit his lip hard, refusing to cry out, though inside he felt the pillar that supported his world collapse completely.
Sensei had promised to come back for dinner. He had promised to teach him Sun Breathing. He had promised to watch him become a strong swordsman. How… how could he just be gone?
News spread quickly across headquarters, and silence fell over the entire Corps.
The Water Hashira, Tomioka Giyu—the quiet, meticulous swordsman who always protected others without a word—was gone.
Killed by an unknown Upper Moon demon, leaving not even a body behind.
Anger burned through the ranks like wildfire. The Kakushi gripped their swords with white-knuckled hands, nurses at the Butterfly Mansion packed Giyu's belongings through tears, and the remaining Hashira gathered in the main hall for an emergency meeting.
No one spoke first. The only sound was the heavy, uneven breathing of grief.
Kanae was the first to go looking for Kocho Shinobu.
She knew her sister too well—when Shinobu was in pain, she smiled even more brightly, pretending everything was fine while burying her emotions deep inside.
Inside the lab, Shinobu sat at the desk, holding a test tube, studying the liquid inside with sharp focus.
Her lips even curved in a small smile, no different from her usual expression.
"Shinobu," Kanae called softly.
Shinobu turned around, smiling. "Nee-san, you're here. Perfect timing. Tamayo-san and I just extracted a new toxin—it's three times more effective at breaking down demonic cells than the last one. We'll have a much better chance when facing the Upper Moons now."
Kanae stared at her sister's smile, her chest twisting painfully.
She walked forward and pulled Shinobu into a hug. Tears streamed down her cheeks. "Stop pretending, Shinobu. I know you're hurting. Giyu's gone. It hurts, doesn't it?"
Shinobu's body stiffened, her smile vanishing instantly.
She wanted to say "I'm fine," but the words stuck in her throat. Not a single sound came out.
All the tension she'd been holding back shattered. She leaned against her sister, her shoulders trembling as she whispered, almost too softly to hear, "Nee-san, I'm fine… really. I still have to work with Tamayo-san. We'll make the deadliest poison in the world… and make those demons pay."
"I know, I know…"
Kanae patted her back, voice breaking. "But don't push yourself too hard. It's okay to cry. I'm still here."
A month later, Tō and Tanjiro finally found the courage to visit the Butterfly Mansion.
When they entered the lab, Shinobu was bent over her desk, writing a report. She looked up, smiling gently the moment she saw them.
"Tō, Tanjiro, you're here. Sit down. I just brewed some tea."
But Tō didn't sit. He stayed where he was, staring at her quietly.
He could see the "threads" of people's emotions—normally, Shinobu's were a calm, soft blue.
Now, they were violently flickering, burning bright red like flames, each thread pulsing with anger and sorrow.
Tanjiro frowned slightly. His heightened sense of smell caught it too—
Beneath the herbal scent that always clung to Shinobu, there was another overwhelming odor.
The sharp, suffocating scent of rage.
The smell in the air was heavy—heavier than any demon stench Tanjiro had ever encountered before.
"Shinobu-san," Tanjiro hesitated, then finally spoke. "Are you… angry?"
Shinobu paused, her pen freezing midair. "Why do you ask that, Tanjiro?"
"I can smell it," he said softly. "There's a strong scent of anger around you… and sadness, too."
He glanced toward Tō. "Tō can see it too, right?"
Tō nodded, his voice rough. "Shinobu-san, the threads around you… they're shaking. They're red—burning red—and so hot it hurts to look."
Shinobu fell silent.
She had thought she hid it well, but these two boys had seen right through her.
Setting the pen down, she leaned back in her chair. The gentleness in her eyes faded, replaced by exhaustion and the weight of fury.
"Yes. I'm angry. Angry that I'm too weak—angry that I couldn't create a poison strong enough to kill the Upper Moons sooner. Angry that Tomioka-san is gone, and we don't even know which demon did it. Angry that those monsters can take the lives of people we care about whenever they want…"
She stopped for a moment, then smiled again. But this time, her smile carried steel beneath it.
"But anger won't fix anything. I'll turn it into strength instead. I'll make the strongest poison. I'll avenge Tomioka-san. Every demon that's ever hurt our comrades will pay for it—with everything."
Tō and Tanjiro said nothing.
They both knew—this unshakable resolve was what kept Shinobu moving forward.
They bowed and left the lab.
Outside, sunlight fell across their faces—but it felt cold, empty.
"Tō," Tanjiro said quietly, "you haven't moved on either, have you?"
Tō shook his head, his eyes red. "Every day, I train with my sword until my arms go numb. But I still miss Sensei… He promised to teach me Sun Breathing. He hasn't even seen how strong I've become…"
Tanjiro placed a hand on his shoulder and said nothing.
He understood completely. He too practiced the Hinokami Kagura every day, pushing himself harder, hoping to grow stronger—to find the demon who had killed Giyu and avenge him.
At the emergency Hashira meeting, Ubuyashiki Kagaya sat in his wheelchair, his face pale but calm.
"Based on the Kakushi's investigation and Tamayo-san's examination, we can confirm that Tomioka Giyu has fallen in battle. The culprit is an Upper Moon. The black blood found at the site cannot yet be identified."
"Can't be identified?"
Uzui Tengen slammed his fist into the table, his silver-lavender hair swaying with anger. "We're just letting that demon run free? We need to find it—now—and avenge Giyu!"
Himejima Gyomei pressed his hands together in prayer, his voice heavy and deep. "We'll increase patrol coverage in every region. If there's any trace of an Upper Moon, we'll alert all Hashira and move together. Giyu's death must be avenged."
Tokito Muichiro gripped his Nichirin Sword, eyes sharp as blades. "I'll search the northern border myself. Since that demon appeared in Kirigakure Village, it's likely still nearby."
Kanae looked around at everyone, her tone firm. "Shinobu and Tamayo-san will speed up their research on the poison. We have to find the one who killed Giyu—avenge him, and everyone else taken by demons."
Anger burned through the meeting room once again—but this time, it carried with it a steady, shared determination.
None of them knew that the one who had killed Giyu was Upper Moon One, Kokushibo. None of them knew that Giyu wasn't truly dead—that he had become the new Upper Moon Six.
But they knew this much: no matter who the killer was, no matter the cost, they would find the demon and make it pay.
Outside, the wind passed through the courtyard, carrying a chill—but it couldn't cool the fire of vengeance or the resolve burning in the hearts of the Demon Slayer Corps.
This war between humans and demons, ignited by Giyu's "death," had only become more brutal—yet their faith in protecting the living world had never been stronger.
…
Somewhere far away, Giyu suddenly sneezed.
He rubbed his nose, frowning.
"Strange… can demons catch colds too?"