The journey was long and silent.
The masked swordsman didn't speak unless necessary. He called himself Kurogiri, a minor member of the Demon Slayer Corps. His black cloak bore no color on the back—meaning he was no Hashira. But he moved like a man used to war. Sasuke recognized that gait.
They traveled across dense forests and through hidden paths that wound along streams and mountainsides. Kurogiri offered no explanation of where they were going, only that they were "headed to headquarters."
Sasuke didn't ask questions. He observed.
No chakra signatures… he thought. But breathing—each person's breath—has a presence. A rhythm.
It was foreign. Yet somehow, familiar.
Three days later, they reached a training facility nestled in a valley surrounded by cedar trees and waterfalls. The smell of damp earth and blood hung in the air. Wooden dummies were scattered around the field—many of them sliced in half or charred by recent training.
Sasuke was ushered into a stone courtyard, where a tall figure waited: a woman dressed in a deep purple kimono, with pale lavender eyes that glowed like starlight. Her presence was unsettling.
This was Shinobu Kocho, the Insect Hashira.
"So… you're the wild boy who beheaded a demon without a proper sword?" she said sweetly, hands folded behind her back.
"I killed it because it was going to kill a child," Sasuke replied flatly.
Shinobu tilted her head. "And what are you, exactly?"
"Just a man who used to fight monsters."
Her smile thinned. "Then you'll fit right in."
Sasuke was taken to a testing ground—wide and empty except for wooden posts and dummies. A pair of Demon Slayer trainers stood by with practice swords.
"Show me how you move," Shinobu said, sitting casually atop a rock. "Fight without killing."
Sasuke stepped forward, silent.
One of the trainers rushed at him, blade raised. Sasuke dodged effortlessly, leaning just outside the strike's arc, then struck the man in the gut with the hilt of his practice sword.
He pivoted as the second trainer approached, sweeping his leg out and knocking the attacker to the ground with fluid, dance-like grace.
In three seconds, it was over.
Shinobu clapped slowly.
"You don't move like a beginner. But you also don't breathe like a swordsman."
Sasuke narrowed his eyes. "Breathe?"
Kurogiri stepped forward and explained in a gruff tone. "To fight demons, we use special breathing styles. Techniques that allow the body to reach superhuman power without chakra or magic."
"…Breathing styles?" Sasuke muttered.
The concept intrigued him. Breath as a power source. As focus. It was like chakra control, but deeper. More instinctive.
Shinobu gestured, and a girl walked forward carrying a Nichirin Blade. "Try it," she said. "Hold it. Swing it. See if it speaks to you."
Sasuke accepted the sword and held it up. It was heavier than expected, but beautifully balanced. As he gripped the hilt and took a testing swing—
Something stirred.
A pulse.
A memory.
The blade shimmered faintly in the sunlight—then, as he exhaled slowly, the air around it dimmed for just a moment.
A strange chill rippled along his arm.
Shinobu's smile faded.
"His breathing… it shifted. Did you feel that?"
Kurogiri nodded. "It was like… moonlight being swallowed."
Sasuke closed his eyes.
He focused—not on chakra, not on ninjutsu—but on the rhythm of his lungs, the beat of his pulse, the stillness between breaths. He had once controlled fire and lightning with thought. Now, he had to learn to fight with breath alone.
In that moment, the first words came to him, unbidden—etched into his soul.
Shadow Moon Breathing, First Form: Phantom Slash.
He opened his eyes and swung.
A line of wind burst forward. It didn't cut—but it echoed. A phantom arc shimmered in its wake before vanishing.
The air was dead silent.
Shinobu rose from her rock, brows furrowed. "That wasn't any Breathing Style I've ever seen. It wasn't Moon Breathing… nor Flame…"
Sasuke lowered the blade. "It's mine."
That night, he was given quarters in a remote cabin. He stared out into the forest, the moon rising like a watchful eye.
He wasn't sure what this world wanted from him. But one thing was certain:
The demons here needed killing.
And now, he had a new way to do it.
Not as a shinobi.
But as something new—something forged in the dark, beneath the moon.