Tamayo—once a human woman—had been deceived by Muzan Kibutsuji centuries ago. At the age of nineteen, she was turned into a demon.
And in the frenzy of that transformation, she lost control—slaughtering her husband and young children with her own hands.
Yet even amidst that tragedy, her hatred for Muzan burned stronger than her bloodlust. Through sheer will and intellect, she managed to suppress Muzan's curse for a short time and used her medical knowledge to experiment on herself—diminishing her craving for human blood.
Now, by consuming small amounts of donated blood on a timed schedule, she could live rationally, maintaining her sanity without ever harming a soul.
The young man beside her, Yushirō, had once been a dying human. Two centuries ago, Tamayo had transformed him into a demon using her own blood. Like her, he survived on stored blood instead of hunting humans.
Hearing this, Tanjiro's expression softened with dawning comprehension.
"So that's why your scent is different… you don't carry the same smell of blood and decay as other demons."
Tamayo nodded, though her gaze soon turned toward Chika.
"Miss Chika, you aren't a demon… and yet, there's a faint trace of demonic essence on you. And this girl"—she looked toward Nezuko's box—"she is a demon, but her scent is lighter than even ours. Please—tell me what happened to you both."
Her tone was earnest, almost pleading. If Yushirō hadn't restrained her, Tamayo might have bowed right then and there.
Normally, dragging up another's trauma would be inexcusable—but Chika didn't mind. Those memories were ones she relived in her dreams often enough; she was already "used to" the pain.
And so, she began recounting that night—the night the Kamado family was annihilated.
Tanjiro sat in silence, listening.
Even he didn't know the full story of what his sister had endured. As Chika spoke, the air grew heavy. It was as though her words painted the scene before them: the moonlit snow, the scent of blood, the helplessness of standing before an overwhelming force.
They could feel it—the sheer futility. Muzan Kibutsuji, the Demon King himself… a being standing at the very summit of existence.
To him, slaughtering a defenseless mother and her children wasn't even an act of cruelty—it was instinct.
Tanjiro's fists clenched. His jaw trembled. His red eyes burned darker, fiercer.
Unforgivable. Unforgivable!
Tamayo, too, lowered her gaze. The rage she'd carried for centuries stirred anew.
By the time Chika finished, an unspoken understanding had formed between them. Tamayo extended her hand, and Chika took it.
Enemies no longer—kindred spirits bound by the same hatred.
Tamayo, a doctor devoted to researching a cure for demonhood, also sought a medicine capable of killing Muzan himself.
And though her progress was slow, her reasoning was sound—after all, Muzan had not been born a demon. He had once been human, until a physician's experiment transformed him into the monster he became.
At that thought, Tamayo turned to Chika with hopeful eyes.
"Chika… would you allow me to take a small sample of your blood? And perhaps some from Nezuko as well? I'd like to study it—just a little."
"Of course," Chika said without hesitation.
"Thank you—truly!"
Tamayo's gratitude was sincere. She handed Chika a small medical kit, and Chika pricked her arm to draw a vial of blood before handing it back.
Tamayo examined it with clinical fascination. To the eye, it looked perfectly ordinary—yet as she watched, the tiny cut on Chika's skin was already clotting and healing before her eyes. Not with the regenerative speed of a demon—but far beyond that of any human.
"Incredible…"
Even Yushirō, who had been glaring suspiciously this whole time, couldn't help but mutter in disbelief.
Once Nezuko's sample was collected as well, Tamayo looked up from her instruments.
"If possible, could you also bring me blood samples from higher-ranked demons when you encounter them? It would greatly accelerate my research."
Tanjiro accepted the small blade Yushirō offered—a specialized tool for quick blood collection—and nodded firmly.
"Understood. We'll bring back whatever we can."
But before he could ask any further questions, Tanjiro froze.
A scent—so faint, yet so unmistakable—drifted into his nose.
That smell.
That smell.
He had only ever smelled it once before.
The night his family was slaughtered.
Muzan. Muzan. Muzan!
His breath quickened. His heart pounded violently. He shot to his feet, turning toward the direction of the scent, rage twisting his face.
Without thinking, he took a step forward—ready to charge.
But a firm hand landed on his shoulder.
"Tanjiro. Calm down."
He turned—Chika was standing beside him, eyes sharp, voice steady as stone.
"B-but, Sister! It's him! Muzan!"
"And what then?" she said quietly. "Do you honestly think you can defeat him now? You've barely fought a strong demon yet—and you think you can take on the Demon King himself?"
Her words struck like cold water.
Chika remembered the crushing pressure she'd once felt in Muzan's presence—the hopelessness that froze even the soul. And she knew the truth of the story: the only reason Tanjiro had survived his first encounter in the original tale was because Muzan had chosen to retreat.
But if fate shifted even slightly—if Muzan decided to test him instead of fleeing—it would be over in an instant.
"Now isn't the time," Chika said firmly. "We'll get stronger. We'll train. And one day, we will settle that score. But not like this."
Her calm certainty grounded him. Slowly, Tanjiro exhaled and sank back into his seat.
"You're right… Sister. Even Sensei wouldn't stand a chance against Muzan right now. We're nowhere near ready."
He paused, eyes thoughtful. "But… what does he look like? The one who did this—Muzan. What kind of face does he have?"
Chika blinked. Then, before she could stop herself, the first image that came to mind slipped out of her mouth.
"Michael… Jackson?"
"…Huh?"
Tanjiro stared. So did Tamayo. Even Yushirō looked confused.
Tamayo tilted her head, genuinely curious. "Michael… Jackson? I don't believe I've heard that name. Is he someone you know?"
Chika coughed awkwardly, averting her eyes.
"Ah, no, no—just… a figure from a dream, I guess."
Right. Distant future. Whole other world. He's not even born yet, she thought grimly.
And so, with a faint, embarrassed smile, she waved it off.
"Forget I said that."