In the depths of the Infinity Castle, where walls shifted like ripples across water and time bent to Muzan's will, the air grew still.
Akaza knelt, bloodied and trembling, before the king of demons.
Muzan's eyes glowed crimson in the darkness. He loomed above, silent and unreadable.
"You failed," he said finally, voice colder than the void.
Akaza bowed his head low. "Forgive me, Lord Muzan. I—"
"I don't want excuses," Muzan hissed.
The tension in the room thickened like tar. The other Upper Moons—silent observers through summoned shadows—watched with hidden amusement and anxiety.
Akaza clenched his fists, trembling.
"I nearly killed the Flame Hashira. If it weren't for him—"
"Him?"
Muzan's voice sharpened.
Akaza hesitated. "The one who intervened. He used… Sun Breathing."
The silence that followed was absolute.
Muzan froze.
Then the room shook.
"You dare speak that name?!" Muzan's form rippled, his human shape shattering for a brief moment to reveal a mass of hatred, tendrils, and eyes.
Akaza's body was flung across the marble floor, crashing into a pillar and coughing blood.
"He used which forms?"
"All of them," Akaza choked out. "All thirteen."
A deep tremble passed through the chamber.
Memories stirred.Visions of Yoriichi Tsugikuni—the only man Muzan ever feared.The swordsman who nearly ended him.
"No," Muzan growled, trembling with fury. "He cannot return. Yoriichi is dead."
Akaza coughed again. "This wasn't Yoriichi. He looked different. Spoke different. But… he fought like him. I saw something through your blood. He's… older. From somewhere beyond."
Muzan's crimson gaze narrowed.
"…Another anomaly. Another threat."
He turned away, cloak billowing in the surreal wind of the castle.
"Find him," he commanded, voice laced with venom. "Send everything. I want his heart… torn from his chest."
The shadows swallowed Akaza whole.
The storm had been noticed.
Far away from Muzan's madness, the sun broke gently over the quiet fields surrounding the Butterfly Estate.
In a secluded glade hidden behind the compound, Tanjiro exhaled deeply, sweat dripping from his brow.
"Again," came Tharion's quiet command.
Tanjiro nodded and moved, his form fluid, blade dancing through the air.
"First Form: Dance."
Tharion watched closely.
"Too tight in the shoulder. Let your movement flow with breath—not against it."
Tanjiro nodded, adjusting.
He began again.
"Second Form: Clear Blue Sky!"
The flaming arc cut through the air, more graceful this time.
Nearby, a tree bore the charred remains of earlier slashes. Tharion had created a ring of stone to protect the grove, insulating their sessions from curious eyes.
They had trained like this for a week now—just before dawn and again after dusk.
No one knew.
Only Nezuko had wandered close once. She sat nearby quietly during each session, her gaze fixed on her brother with proud, protective warmth.
During a short break, Tanjiro sat down heavily, wiping sweat from his brow.
"You never told me… where you learned Sun Breathing," he asked carefully.
Tharion sat beside him, cloak wrapped around his knees. The morning mist curled around his dark hair.
"I didn't learn it here," he said simply. "In my world, breathing styles don't exist. But when I came here… something changed inside me. I remembered movements that weren't mine, instincts that weren't born of me."
Tanjiro blinked.
"You mean… the Sun Breathing found you?"
Tharion nodded. "Or perhaps… it was waiting for me."
There was a long silence.
Then Tharion looked at him.
"You'll need to master all thirteen forms. Not just the techniques—but the cycle. When done perfectly, it becomes endless. That's how Yoriichi nearly killed Muzan."
Tanjiro's hands tightened on his blade.
"I'll do it. I'll master it. Even if it kills me."
Tharion placed a hand on his shoulder.
"It won't kill you, Tanjiro."
He looked toward the rising sun.
"It will make you the sun."
Across Japan, demon activity surged.
The Upper Moons had gone silent—but not inactive. Scouts began disappearing. Villages once safe were found in ruins. The night grew thicker with each passing day.
The Corps noticed.
And though many did not yet understand what was coming, Kagaya Ubuyashiki did.
He gathered the Hashira once again.
"The war," he said softly, "is accelerating."