CHAPTER 15: THE BIWA

Inside the ever-shifting walls of the Infinity Castle, the air was heavy with tension. Doors slammed. Floors twisted. Ceilings stretched into impossible heights.

Mitsuri Kanroji and Obanai Iguro dashed side by side, their swords glinting with deadly intent, their breathing sharp and synchronized.

"This castle's messing with my rhythm," Mitsuri said, breathless but smiling.

Obanai glanced her way briefly. "Focus, Mitsuri. We're not out of danger yet."

Then, without warning—the walls shifted again.

A sudden rumble echoed, and the pair fell through a collapsing floor—only to land in a vast circular chamber. Thousands of biwa strings echoed through the space.

A single figure stood at the center, her fingers poised on a massive biwa.

Nakime.

THE CONTROLLER. Composer of the castle. Manipulator of space.

Her single glowing eye locked on them.

"I've grown tired of mice," Nakime whispered, plucking a chord. The entire room warped.

A hallway shot toward them from the left, spikes protruding.

The floor fell open into a pit of void.

Obanai slashed the ground, catching Mitsuri before she fell.

"She's using the castle itself!" Mitsuri yelled, jumping to the side as a ceiling beam nearly crushed her.

Obanai's blade flicked forward—Serpent Breathing, Third Form: Slithering Serpent Strike.

But Nakime vanished, the walls shifting again. His strike sliced nothing but air.

Mitsuri growled, tightening her grip.

Love Breathing, Fifth Form: Swaying Blaze Strikes!

Her flexible blade spiraled, demolishing pillars and walls, but the castle repaired itself instantly.

"She's invincible in here," Obanai muttered, sweat sliding down his face.

"No…" a voice echoed.

From a far wall, a shimmer of light appeared. Then, a figure slowly faded into sight.

Yushiro.

He placed his fingers on a paper charm on his forehead—Blood Demon Art: Illusory Sight Override.

"I've hijacked her vision," he said. "I can't hold it long. Now's your only chance."

Nakime's eye flickered—suddenly her movements paused. The castle stuttered.

Obanai didn't hesitate.

"Mitsuri—now!"

The two Pillars soared into the air—like twin comets crashing toward a single point.

Mitsuri's whip-blade coiled around Nakime's arm, pulling her tight.

Obanai's katana gleamed silver in the shifting light—aimed for her neck.

Their blades struck together—

THUNK.

Nakime's head flew into the air, her biwa strings letting out one final dissonant scream.

The castle trembled—its chaotic movement slowed.

Obanai landed on his feet, sheathing his blade. Mitsuri collapsed beside him, panting hard.

"We did it," she whispered.

Obanai didn't speak—he just looked at her, eyes hidden behind his bandages, heart thundering in his chest.

Yushiro nodded from the shadows, already fading.

"One less demon," he said softly. "One step closer to the end."