The Ryūryū Dance—a technique that mimicked the fluidity of water—was meant to overwhelm an opponent with deceptive steps, feints, and surging momentum. Kanzaki Aoi's feet barely seemed to touch the ground as she darted left and right, her wooden sword poised to strike. The sound of her sandals brushing against the stone gave the illusion of water rippling through the night.
It was graceful, efficient, and well-practiced—yet Yukishiro only curled his lips into a sneer.
To him, her elegant movements looked almost… ornamental.
When she lunged, Aoi's confidence was clear. She had sparred countless times before, trained relentlessly in Water Breathing. This boy—an outsider who didn't even understand the basics of breathing techniques—shouldn't stand a chance.
But Yukishiro lowered his body, copying the exact stance of a sword draw. His pale hair glinted faintly beneath the moonlight, his expression calm.
He inhaled, sharp and deep, and when the gap closed to less than a meter, his sword slashed forward.
His movements weren't clumsy or panicked—they were smooth, instinctual, like muscle memory carved into bone.
Aoi blinked. "What? He's moving like a trained swordsman…"
Her grip tightened. "No matter. Technique without breathing won't win against me."
She raised her blade with both hands, driving the point straight toward his throat. The instinct to target the neck was second nature. That was where a demon's life ended; their training always aimed there.
Against another human it might seem ruthless, but this was only practice with wooden swords. At most, he'd collapse in shock.
Yukishiro's lips moved. His voice was low, almost carried away on the night wind.
"Cold Wave."
Two words.
No one in the Butterfly Mansion audience had ever heard of such a technique.
Aoi's blade was only a breath away from striking true when the world shifted. The air thickened, heavy with frost. A shiver tore through her body. Her lungs spasmed. The instant she inhaled, icy air knifed into her chest, biting and sharp.
Her breath stuttered. She coughed, once, twice, and the rhythm of her technique faltered.
Yukishiro sidestepped with ease, his wooden blade arcing toward her back.
How—?! Panic surged in her chest. "The temperature—he lowered it somehow? This isn't possible…"
For an instant she saw defeat.
"Water Breathing, Fourth Form—Twisting Whirlpool!"
Her body spun violently, the centrifugal force forcing her lungs to work, driving her blade outward in a desperate, spiraling slash. The whirl of motion barely managed to deflect his strike. She used the momentum to hurl herself backward, widening the gap, her chest heaving.
The wooden swords cracked together with a sharp clack! before she stumbled back several paces, coughing furiously.
From the veranda, the Butterfly Mansion attendants whooped and clapped, oblivious to the strain in Aoi's body.
"Come on, Sister Aoi!"
"Show him the strength of the Corps!"
"Don't let this rude boy win!"
Their voices rang brightly in the moonlit yard, but only Shinobu watched with narrowed eyes. She had seen it clearly.
The moment Yukishiro uttered "Cold Wave," a pale mist had bled into the air, curling low around his feet. The temperature shifted unnaturally, creating a thin veil of frost.
It wasn't mere theatrics—Aoi's body had truly reacted. Her coughs weren't feigned.
"Interesting, Shinobu thought, her smile deepening. So it's not only technique. His environment responds to his breath…"
Beside her, Kanao sat quietly, chewing the grape Shinobu had playfully slipped into her mouth. When Shinobu leaned over and whispered, "Kanao, who do you think will win?" the younger girl only tilted her head before shaking it.
Shinobu chuckled. "Don't know? Then maybe this boy has a chance."
Yukishiro, meanwhile, stood upright and relaxed, unaffected by the frost-laden air around him.
His pale hair drifted faintly in the breeze, his breathing steady.
Aoi, by contrast, clutched her chest, still recovering from the invasive chill that had burned her lungs. She glared at him, sweat beading along her brow despite the cold.
"Why isn't he affected? He's breathing the same air…"
Unbeknownst to her, the answer lay in his past.
Yukishiro had grown up near snowbound mountains, where winter reigned eternal. His lungs had adapted to biting cold since childhood, blood cells sluggish yet enduring. Where others felt constricted and suffocated, he thrived.
Not only that—his senses worked differently. Just as Kamado Tanjiro could smell emotions on the wind and Zenitsu could hear the faintest tremor, Yukishiro perceived temperature. Every shift of air, every ripple of movement left a trace of warmth or cold. Within his "Cold Wave," any intrusion lit up his awareness like fire against snow.
Aoi wiped her mouth with the back of her hand. She refused to falter, though her pride stung sharply. "This boy… if he had pressed that last attack, I might've been defeated."
Her eyes softened just a fraction. "He didn't. He held back. Maybe he isn't so bad after all".
Still, she couldn't ignore the pressure he radiated. For the first time, she acknowledged him as more than a patient or nuisance.
"Is this… really a breathing style?" she asked hoarsely.
Yukishiro tilted his head. "I told you, I don't know what you mean by 'breathing styles.' But if it's using your breath to fuel your movements, then sure. Call it that if you want. Now—are you still fighting, or not?"
Aoi steadied herself, planting her wooden sword in front of her like a stake. "Fight. Of course I'll fight. Don't think you've won just because of one strange technique. I'm a trained member of the Demon Slayer Corps. If I can't beat a layman like you, I may as well go home and embroider."
Her words were sharp, but her heart raced. She had no idea how to counter him. Direct confrontation was too risky; his frost-breathing disrupted her rhythm.
"Fine. I'll adapt."
She shifted her stance, deciding to breathe shallowly at the edges of her lungs, never too deep, never drawing in too much of that freezing mist. She would rely on her footwork, strike fast, then withdraw to breathe again in the clear. It wasn't elegant, but it was survival.
Yukishiro gave a short laugh. "You talk too much."
And then he moved.
His wooden sword flashed pale beneath the moonlight as he lunged forward, the air shimmering faintly with cold. Aoi bent her knees, preparing to answer.
The second round of their duel had begun.