As a Grey Knight In Naruto

Chapter 38 – Furnace of Flesh

The earth breathed in silence below and outside of Tanzaku Quarters.

Beneath meters of solid stone, where light never reached and no life stirred, a sanctum pulsed with quiet activity. In that still, sterile underground chamber, Hajime stood shirtless beneath the glow of psychic light. His shadow stretched behind him, elongated by the floating threads of Warp energy that flickered like ghostly filaments through the air.

Suspended before him in a cradle of psychic force was a gland, unfinished, embryonic. No larger than a child fist, its form resembled a condensed adrenal lobe, pulsing faintly within a gelatinous membrane. It was still growing.

The Biscopea.

A synthetic organ designed not by nature, but by knowledge stolen from another universe. Hajime had no machines, no automated genecrafting tools like the Apothecaries of the Imperium. But he had something even greater, perfect will.

And the Warp bent to that will.

He extended a finger, and a thread of golden Yang chakra slipped into the chamber around the organ. It slithered between cell structures, triggering accelerated growth, simulating the biological signaling of stem cells differentiating into hormone-producing tissue. Every step of its creation was deliberate, microscopic instructions etched into biomass by thought, psychic energy, and chakra working in concert.

The Warp fed him limitlessly. There was no fatigue. His mind burned with ceaseless clarity. Even as others slept above, Hajime needed no more than two hours of meditative rest. His body was strong, self-regulated, and enhanced by gene-seed optimization. There was no degradation.

And so, he worked through the night.

Three nights had passed since he began crafting the Biscopea. It was nearly complete.

It would be his next transformation.

This organ would regulate hormone output, stimulate dense muscle growth, elevate testosterone and regenerative signals, and interface with his nervous system to maintain perfect hormonal balance. Not wild power, but disciplined strength, the kind of muscle that could crush stone without needing to swell grotesquely.

Enables muscles to grow denser, not just larger, giving Astartes superhuman strength

He focused.

A swirl of blue-white psychic filaments lashed from his palms, wrapping around the gland like threads weaving cloth. His mind directed the fusion of vascular lines with neural inlays, preparing the interfaces that would soon bind to his spine and circulatory system. The Warp responded instantly.

He whispered, almost reverently, "Behind the lungs… just above the diaphragm… anchor to the adrenals…"

He had memorized the anatomical map. The Biscopea would lie deep in the chest cavity, nestled like a sleeping beast between organs, connected to the blood and the brain.

Another pulse of Yang chakra glowed through the gland. It responded by twitching once, an unconscious flex of life.

It was ready.

He let the gland hover in stasis, suspended within a ring of chakra-infused air, and turned away. His work was done for the night.

Tomorrow, he would implant it.

But even now, he felt no need for sleep. Instead, he ascended quietly through the tunnel, emerging in the forest shadows far from Tanzaku's walls. The stars greeted him, silent, glittering, and he walked calmly back toward the clinic.

The morning came with birdsong and warm wind.

Outside the clinic, the wooden veranda basked in golden light as Tsunade sat cross-legged, sipping sake with her usual bleary-eyed expression. Shizune had just brought out breakfast, bowls of miso soup, soft-boiled eggs, rice, and grilled mackerel. Tonton snuffled near the edge of the mat, nose twitching.

Hajime emerged from inside, freshly washed, dressed in a clean robe stretched slightly too tight at the shoulders.

"Breakfast," Shizune said, gesturing toward the tray. "Eat before Tsunade finishes your portion."

"I don't finish his portion," Tsunade grumbled, "he eats like a furnace."

"Because I'm growing," Hajime replied lightly as he sat down.

He reached into his satchel and pulled out a cloth bundle. With practiced ease, he unwrapped it, revealing several off-white bars, each roughly the size of a kunai hilt. They looked like compressed chalk fused with coral.

Tsunade narrowed her eyes. "You're still eating those bone bricks?"

"Calcium bars," he corrected, taking a bite. The sound cracked like he'd bitten a shell. "Mostly fish and ox bones. Ground fine, compressed with a little salt and psychic heat. Easy to digest."

Shizune gave him a skeptical look. "Easy for you. I'd break my teeth."

"They melt down once they hit stomach acid," he assured.

Tsunade stared for a moment, then said with mock seriousness, "You're not human."

He smiled faintly. "That's what you said yesterday."

"And the day before," Shizune muttered.

They returned to their breakfast. The fish was tender. The tea hot. Even Tonton earned a few scraps. But beneath the casual conversation, something quieter lingered, curiosity. The way Tsunade occasionally glanced at Hajime's wrists, noting the thickened bones under his skin. Or how Shizune squinted at the way his jaw had grown sharper, cleaner.

He was changing fast.

And they knew it.

Clinic hours passed in a blur.

Hajime moved through patients with quiet skill, his psychic precision subtly blending into his chakra usage. A twisted ankle, a fevered child, a shinobi with bruised ribs. None of it challenged him anymore. He healed not by procedure, but by insight. His control had become so refined that he could direct tissue repair without even touching a wound.

Shizune noticed, of course.

But Tsunade noticed more.

She watched from across the room as Hajime stabilized a patient's arrhythmia with two fingers pressed lightly to the sternum. No visible chakra. No hand signs. Just presence and intent.

Tsunade's lips pursed as she made a mental note.

He was no longer learning.

He was refining.

That night, Hajime returned underground.

The chamber welcomed him like a second home, cold, clean, sterile. The Biscopea still floated in the stasis field, pulsing with faint life. Hajime stripped off his robe, laying it neatly against the stone. His skin gleamed faintly in the psychic light, muscles lean but corded, veins prominent from clean nutrition and steady mutation.

He reached inward with his mind and silenced pain receptors.

Then, with a steady breath, he activated the chakra scalpel.

There was no hesitation.

A thin incision opened along his chest, just below the pectorals, between the ribs. He widened the cavity carefully, parting tissue without bleeding, sealing capillaries as he moved. Psychic threads held his ribs apart like invisible hands.

The Biscopea floated forward.

He guided it inside.

It nestled against the rear chest wall, slipping behind the lungs, cradled between the adrenal glands and the diaphragm.

Then came the integration.

Psychic filaments stretched from his fingers into the gland, connecting nerve to nerve, vessel to vessel. He fused it with his bloodstream. It began to warm.

Then pulse.

Then activate.

His whole body shuddered.

Not with pain, but with pressure. With fire. The Warp surged through his system like a divine bellows stoking the forge of his blood. The Biscopea flared with life, releasing its first hormonal signals in a cascade of engineered growth.

His muscles twitched.

Veins thickened.

Even his lungs adjusted to the surge, processing oxygen at greater efficiency.

The gene-seed responded almost immediately. It aligned the new organ, optimizing the signals, dampening instability, calibrating his endocrine balance. His adrenal glands merged rhythmically with the new system.

And still, he felt no fear.

Only strength.

He reached for one of the calcium bars nearby, cracked it open, and consumed it in four bites. Then another. The gland had just begun, but already he felt the hunger. Not for food. For material.

His bones are growing.

Now it was his flesh that would follow.

More mass.

More density.

More power.

All under his command.

When dawn touched the mountains above Tanzaku Quarters, Hajime stepped from the forest in silence, his robe freshly folded, body warm from within.

There were three days left before the Chūnin Exams.

And Hajime, who once arrived in this world small, fragile, and cautious, now walked with the poise of something beyond human.

He smiled faintly as the clinic came into view.

There was still more work to do.

But now…

He was ready for anything.

End of Chapter 38 – Furnace of Flesh