The sky was still cloaked in soft morning mist, and the sun hadn't yet fully risen from behind the mountains. Only a faint golden hue began to trace the edges of the horizon.

And yet, a man stood silently outside the small wooden pavilion owned by Tachibana Kyūjō.

His face was pale, his eyes sunken with deep shadows beneath them—clear signs of a sleepless night.

Last night, Kyūjō had finally completed the final version of his newly refined Breathing Technique. For the first time in what felt like ages, he had drifted into a deep, uninterrupted sleep.

But peace, as always, never lasted long.

BAM. BAM. BAM.

A loud, hurried knocking shattered the quiet dawn like a stone tossed into still water.

Kyūjō groaned from his futon, dragging himself up with a look of pure annoyance. He stretched lazily, joints cracking, then shuffled to the front gate, unlatching the wooden lock with no sense of urgency.

Standing there at the entrance...

Was none other than Kagaya Ubuyashiki, the head of the Demon Slayer Corps.

His usually serene appearance was completely wrecked—dark circles under his eyes, hair slightly disheveled, and a stiff tension coiled through his jaw.

Seeing the dignified Oyakata-sama looking so... haggard, Kyūjō couldn't help the crooked smirk that curled at the corner of his lips.

He exhaled a tiny chuckle and teased, voice brimming with playful malice:

"Oyakata-sama... how tragic."

"If you keep pushing yourself like this, you might break, y'know?"

"You're still young—try showing a little restraint."

Kagaya's expression twitched. A vein visibly pulsed on his temple.

He stared at Kyūjō with the kind of look that said: If I didn't need you alive, I'd strangle you right now.

Of course, Kyūjō had said it on purpose.

Who in their right mind sends a message that urgent in the middle of the night? Obviously, he knew Kagaya wouldn't be able to sleep afterward. Diabolical bastard.

Still, Kagaya chose to ignore the provocation. He kept his voice cold and direct.

"The words you sent me last night... What exactly did you mean?"

Kyūjō raised an eyebrow, feigning innocence.

"Which words, exactly?"

Kagaya clicked his tongue in frustration and turned to leave.

But before he could step past the gate—

Kyūjō grabbed his shoulder, eyes shining with something wild and electric.

"C'mon, Kagaya. Follow me."

"I'll show you something."

"The pinnacle of power in this world."

Kagaya stopped mid-step, glancing back with a skeptical frown.

"If this turns out to be another joke... I'll personally expel you from the Demon Slayer Corps. And I'm cutting off your salary too."

Kyūjō's expression went stiff.

He raised both hands in exaggerated surrender.

"Whoa, no need for financial threats, Oyakata-sama! Let's go! Right now!"

And the moment those words left his mouth, Kyūjō vanished.

A flash of yellow-blue lightning surged through the air, engulfing Kagaya as well. In an instant, both of them disappeared, leaving only the scorched scent of ozone and a faint afterimage.

Just seconds later, a squad of elite guards dashed toward the empty pavilion, their faces pale with panic.

"Oyakata-sama?!"

"Where did he go?!"

"There were two people here just now... and now—nothing! How is that even possible?!"

— — —

Somewhere far outside the Demon Slayer Corps' headquarters—

A brilliant flash lit up the forest clearing, and the two figures reappeared in a burst of speed that tore leaves from nearby trees.

Kagaya stumbled slightly, trying to catch his breath.

Even though he'd heard reports—countless ones—about Tachibana Kyūjō's terrifying speed, experiencing it firsthand was an entirely different matter.

So this was the man whispered about in reverent tones across the land.

The one known as—The Lightning Sword Saint from the Sky

Kyūjō stood with his arms crossed, chest puffed out proudly.

"Pretty impressive, right?"

Kagaya's eyes still glimmered with residual shock, but now they burned with curiosity.

"Kyūjō... Have you fully recovered your strength?"

But Kyūjō shook his head slowly. His voice turned quiet—serious.

"You misunderstand."

"I'm not just recovered."

"I've gone beyond the peak of this world."

"Right now... I could crush ten of my past selves without breaking a sweat."

Even if Tsugikuni Yoriichi, the strongest human in history, were to return from the dead...

Kyūjō truly believed—he wouldn't lose.

It might've been arrogance, or maybe pure conviction.

But his belief was unshakable.

— — —

After some time, they arrived at a narrow waterfall tucked deep in a quiet valley.

It wasn't massive, standing about seventeen meters tall and five or six meters wide. But its crashing current echoed loudly, scattering white mist into the air.

Kagaya frowned suspiciously.

"Wait... Don't tell me. You're planning to cut the waterfall?"

Kyūjō didn't answer. He simply smiled.

Then, with fluid motion, he drew the Nichirin Blade at his waist.

The blade's name was Zetsuaku – Soul Calmer.

It hissed softly as it left its sheath, as though rejoicing at being held again after so long.

Kyūjō raised the black blade toward the rising sun. Morning light danced across its edge, illuminating the fine scratch marks etched into the steel—a silent testament to the brutal battle against Kokushibō, Upper Moon One.

He had never repaired the sword at the Swordsmith Village.

Back then, he had no intention of wielding it again.

It was just a memory.

But now...

Now, everything had changed.

Zetsuaku resonated with its master's emotions. The blade trembled gently in sync with Kyūjō's heartbeat.

He traced a finger along the flat of the sword, slow and reverent, like touching something fragile... and sacred.

Watching from behind, Kagaya suddenly felt a chill creep down his spine.

That look in his eyes...

He had never seen anyone gaze at a sword like that.

Like it wasn't just a weapon—but a lover.

Unable to endure the awkward tension, Kagaya snapped.

"Hey! You done yet?! At this rate, the sun's gonna set before you even swing!"

Kyūjō chuckled quietly, then turned to face the waterfall.

"Kagaya. Stand behind me—and take ten steps back."

Kagaya hesitated, then did as instructed, backing away until he stood at a safe distance.

Then it began.

Kyūjō's pores opened wide.

The air around him shifted.

The atmosphere twisted, swirling in a growing spiral around his body, like invisible winds pulling everything inward.

Even from behind, Kagaya could feel it.

The pressure.

The way the air itself seemed to thin, drawn toward one man standing in silence.

Then...

A low rumble echoed from deep within Kyūjō's core.

Thunder. Muffled and primal. As if a god had just stirred in his chest.

He wasn't using standard Thunder Breathing anymore.

This was something entirely different—an evolved form, refined beyond mortal limits:

Thunder Breathing – Version 2.0

A technique that had torn past the natural rules of the world.

With a single, focused movement, Kyūjō spun his energy through every tendon, muscle, and nerve—

And unleashed a single upward slash.

One arc.

One breath.

The blade cut the air clean, too fast for human eyes to follow.

It carved an invisible line that sliced through the entire base of the waterfall.

And in the next heartbeat—

WHOOOOM!!!

Water exploded upward—yes, upward—defying gravity, surging toward the sky like a great dragon ascending.

The entire waterfall erupted into chaos, and then came crashing back down in an avalanche of roaring white spray...

Right where Kagaya was standing.

He didn't even have time to dodge.

In an instant, the refined and composed leader of the Demon Slayer Corps was drenched head to toe—drenched so thoroughly he looked like a drowned rat pulled from a well.

He stared at Kyūjō in stunned silence, water dripping from his chin.

Kyūjō, still standing proudly, hadn't moved an inch.

"So... the reason you told me to stand ten meters back... was just to make sure I got soaked like this, huh?!"

A single slash beyond logic.

But more than that...

An unforgivable prank.

— — — — — — — — — — — — — — — —

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