To force Kibutsuji Muzan to show himself, Nightingale had once left the Demon Slayer Corps to search for the Blue Spider Lily.
Though she didn't know exactly where to find the Blue Spider Lily, she knew whom to ask.
Both Kamado Tanjiro and Kamado Nezuko had managed to overcome sunlight after becoming demons, leading some to speculate that the legendary Blue Spider Lily—which could supposedly grant demons that power—was growing somewhere in the Kamado family's backyard… Nightingale wasn't sure if that rumor was true, but she did recall a memory in Tanjiro's mind: a fleeting glimpse of a blue spider lily.
So, Nightingale paid a visit to the Kamado home, and it was after this that she happened to meet Tamayo.
The Kamado family lived at Mount Kumotori in Okutama—the highest peak in Tokyo, rising 2,017 meters above sea level.
When Nightingale arrived at the Kamado household, she was surprised to find that Tanjiro's father, Kamado Tanjuro, was still alive. He was frail and sickly, but hadn't yet passed away.
Tanjuro and Tanjiro looked alike in many ways—both had the same deep red hair, both bore a scar on the left side of their foreheads. But Tanjuro's face was sallow and thin, his body weak, wracked by constant coughing.
Though Nightingale's original purpose had been to seek the Blue Spider Lily, seeing Tanjuro's condition, she immediately set her quest aside to nurse him back to health.
His body was so frail that any aggressive treatment would only do more harm. Nightingale could only use gentle, patient care, allowing him to recover bit by bit.
Witnessing Tanjuro's slow but steady recovery, the Kamado family was immensely grateful. So when Nightingale finally asked about the Blue Spider Lily, Tanjiro's mother, Kie, agreed without a moment's hesitation.
Kie Kamado knew exactly where the flower grew. The reason it had appeared in Tanjiro's memories was because, as a child, Kie had once brought him to see it.
The Blue Spider Lily really did grow near the Kamado home—and the place where it bloomed was the grave of Tsugikuni Yoriichi's wife. After Yoriichi's wife was killed by a demon, he had planted the flower at her grave.
Maybe this is fate… For a thousand years, Muzan had searched for the Blue Spider Lily, and yet, again and again, he'd passed right by it.
The thing you most want to find… is hidden in the place you least want to look.
Because the flower would not bloom for some time, and because Tanjuro's care required patience, Nightingale ended up staying with the Kamados for almost a year.
On her last day there, as Tanjuro's health had finally improved, he came to Nightingale, intent on repaying her kindness.
I only did what anyone in my position should—bringing healing to those in need is my duty… I don't require any reward… Nightingale tried to refuse, but Tanjuro was unexpectedly stubborn—he insisted on expressing his gratitude.
As thanks, he performed the Kamado family's ancestral kagura dance, the "Hinokami Kagura," in front of Nightingale.
Tanjuro explained that the dance was an offering to the fire god for peace and safety, but Nightingale saw clearly—Hinokami Kagura was none other than Sun Breathing, the original and source of all Breathing Styles.
Long ago, when Yoriichi was a Demon Slayer, he had once saved Tanjiro's ancestor, Sumiyoshi. After being banished from the Corps for letting Muzan escape, Yoriichi visited Sumiyoshi one last time and passed Sun Breathing on to the Kamado family, and so it became the "Hinokami Kagura" they had inherited.
Despite knowing all this, Nightingale felt little interest in Sun Breathing itself.
Yoriichi truly was a genius—if he'd been born in the world of Type-Moon or anywhere else, his achievements would have been even greater… But this world is too small; it stunted his growth. The Sun Breathing style that's considered unattainable here… is nothing special to me.
During my time with Kanae and the others, I picked up Flower, Water, Flame Breathing, and the rest just by watching once. Sun Breathing is the root of them all—learning it was even easier for me.
Yet, in the next moment, Nightingale's calm red eyes widened in shock.
Before her, as Tanjuro danced the Hinokami Kagura on the packed earth, the figure before Nightingale's eyes began to change.
His deep red hair, tied high, flickered like a living flame; a fire-shaped Mark bloomed near his left eye; his irises burned scarlet; a pair of sun earrings hung from each ear; his red haori fluttered over a yellow kimono.
As he danced, he seemed less like a man and more like a spirit of the sun.
Then, suddenly, that figure turned, red eyes meeting Nightingale's.
He smiled, gentle and relieved.
"I'll leave it to you."
That's what he said.
Nightingale blinked, stunned, and by the time she tried to focus again, Tanjuro's demonstration was over—and the otherworldly figure had vanished.
How strange… Let me take another look—wait, where'd he go?
The next day, with her heart tangled in complex emotions, Nightingale left the Kamado home.
She'd only meant to pick a flower. Instead, she'd spent nearly a year nursing someone back to health… and, somehow, ended up accepting a request.
And I didn't even get to refuse! He just said his piece and disappeared!
I mean—come on! It's not like I would've said no, so why run off like that?
…
Back on the battlefield, everything was in ruins.
Huge, savage sword scars crisscrossed the land as far as the eye could see.
The storm of sword energy that had wrought such devastation had long faded, leaving only scraps of torn clothing—and, hidden within, a broken flute.
Inhale… exhale…
For the first time ever, Nightingale had flawlessly executed the legendary Sun Breathing technique.
The surging flames of the sun wrapped around her, and just looking at her silhouette felt like having your eyes burned, as if you were staring straight into the noonday sun.
With Sun Breathing, she had ended Kokushibo's life. That was the reason she hadn't killed Muzan immediately upon capturing him.
After all, once Muzan died, Kokushibo would die too.
Now that Kokushibo was gone, Muzan no longer needed to be spared—she could destroy him right here and now.
Just then, Nightingale suddenly felt her hand grow light.
Kibutsuji Muzan's head, which she'd been holding, slipped from her grasp. Before it even hit the ground, it turned to black ash, scattering on the wind.
Kibutsuji Muzan was dead—dead in an instant.
Even Nightingale looked genuinely surprised.
A little earlier…
With only his head left, Muzan had been putting on a show of docility. In truth, every moment, he was straining to break down the poison inside him.
Damn this lunatic woman, humiliating me like this… I am the Demon King! I am a being who has half-stepped into immortality! Once I neutralize this poison and finish digesting the Blue Spider Lily, I'll slaughter the entire Demon Slayer Corps! I'll make this madwoman wish she could die, but never let her!
And those idiots… Even though I weakened myself before the battle by sharing my blood, they were still so useless! Couldn't even buy me time! Even Kokushibo—how did it take him this long to kill a few Hashira? Worthless! None of them could find the Blue Spider Lily or kill the right people!
It's almost done, almost… just a little more…
Muzan, battered down to a single head by Nightingale, was extremely weak. If the poison spread any further, he would die, so he focused on containing it—isolating it in one place before slowly breaking it down.
He had almost finished by the time Nightingale dragged him to Kokushibo's battlefield.
Just a bit more! The hope of immortality is right in front of me!
He kept up his act perfectly—eyes blank, mind sharp, ignoring all distractions, working toward his goal.
But when Kokushibo unleashed his massive sword technique, even Muzan was startled—at that moment, without his regenerative power, Kokushibo could've killed him too.
Kokushibo! You traitor! Why didn't you fight this hard against the Hashira? Are you aiming for my throne, you bastard? Do you want to be the next Demon King?!
After cursing Kokushibo in his heart, Muzan suddenly realized his focus on the poison was slipping, and he frantically redoubled his efforts.
Until… that familiar sunlight blazed again.
No doubt.
He couldn't possibly mistake it.
That's Sun Breathing! The very same technique Yoriichi almost killed me with!
In an instant, his pupils shrank to pinpoints, a tidal wave of terror swallowing him, as if he were drowning in a bottomless sea.
The moment his eyes caught the flash of flame, Muzan felt a pain that seemed to burn his soul to ashes.
Even after centuries, even after devouring countless humans, the wound Yoriichi left in him had never healed, tormenting him all these years.
Fear—rooted in every cell of his being.
Each cell shrieked in agony, desperate to escape. Each cell seemed to have a mind of its own—but all wanted only one thing: to get as far from that searing sun as possible.
Reason evaporated. He couldn't think at all.
And with that, Muzan completely lost control over the poison inside him.
The toxin that could kill demon cells, finally freed, tore through Muzan's body like a starving wolf among sheep. But lost in terror, Muzan didn't even notice.
And so, Muzan died.
Scared to death by Nightingale's Sun Breathing.
Nightingale had been considering letting the Demon Slayers take their vengeance, giving them Muzan's head to vent their anger—after all, with her around, Muzan couldn't stir up any more trouble.
But before she could do anything, Muzan just… died?
Is this supposed to count as faking an injury?
But this was no time to ponder such things.
A tremor shook the ground beneath her feet—the entire Infinity Castle began to shudder violently.
"What's…?"
Nightingale realized what was happening.
"The Infinity Castle… is collapsing!"
The Infinity Castle was an extradimensional space created by Nakime's Blood Demon Art. Now, with the source of all demons—Muzan—dead, every demon he'd created or controlled would vanish, Nakime included.
When Nakime died, the Blood Demon Art supporting the castle would collapse too.
If a house collapses, you might survive being trapped or buried. But if this extradimensional space itself fell apart, anyone left inside would be destroyed along with it.
She needed to find the exit, and get everyone out before the castle crumbled.
But…
Muichirou and Iguro… and so many other Demon Slayers are too far away… There's no time!
The groan of grinding gears grew louder and louder—the shaking of the Infinity Castle worsened.
If I use the Holy Savior Blade, I could stabilize this space temporarily—or maybe send everyone out before the castle breaks apart…
Though she instinctively recoiled at the thought of using the Savior's Blade, what she absolutely couldn't accept was watching lives slip away before her eyes.
Just then, a wooden door suddenly opened at Nightingale's feet.
Not just for her—Kochou Shinobu, Tomioka Giyuu, Rengoku Kyojuro, and the others all saw doors appear beneath them as well.
At the same time, every Demon Slayer inside the castle—crying tears of relief after the demons vanished—had doors open under their feet. Before they could react, they were all dropped through, sent back to the real world.
At the center of the Infinity Castle, two figures stood.
One, her face hidden by long black hair, sat cradling a biwa—Nakime, the master of the castle.
The other was Yushirou, who was using his Blood Demon Art to control Nakime, guiding the Demon Slayers out one by one.
"Damn that Muzan… Even dead, he manages to make such a mess…"
Yushirou muttered to himself, veins standing out, sweat pouring down his face—the strain of controlling Nakime was clearly immense.
Still, he gritted his teeth and endured… even though the deaths of humans had never really mattered to him.
"That crazy woman… Just remember this—I owe you nothing from now on!"
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T/N: WOAH YUSHIROU ACTUALLY A GOAT???