Jujutsu Kaisen: False Dawn

The Living Core Hypothesis—Chapter 137

"Use the Inverted Spear of Heaven as the base… Let Kai2 be the cursed-energy core… and make Flood Maw the embedded cursed technique."

The idea hit and wouldn't let go.

Ren was already on his feet, pacing tight circles across the bedroom floor, hands flicking as if he were sketching sigils in the air.

"Structurally, the only 'loss' is that Kai2's form as a curse will be altered. That's fine. In fact, I can reinforce the whole thing. I understand Magnetic Decree—I know how metal behaves under cursed energy. With Red Stitch, I can lay a circuit inside the metal… no—better—make the blade itself out of the circuit."

He stopped, eyes widening.

"Yeah. Red Stitch becomes the blade. The Inverted Spear is the spine, the anchor. Then I stack binding vows, use the 'copy' understanding to pass Flood Maw into Kai2, and fuse the three layers: base—core—technique."

The plan built itself, piece by piece.

"That would give the sword a perfect cursed-energy circuit. If the circuit is mine—if it's Red Stitch—then syncing it to my own circuit becomes trivial. Feed it cursed energy effortlessly. Use Flood Maw through it, like breathing. And since I already understand curses through Cursed Spirit Manipulation, I can shape Kai2's form correctly as a core."

He blinked, realization sinking in.

"…This could turn Kai2 into the first living cursed tool."

Silence. Then a grin.

"Is it even possible? Sukuna split himself into twenty fingers. If he could do that, turning Kai2 into a blade is nothing. There it is… I thought I'd lost it—the genius. I got comfortable after Rika. Lazy. Now that I don't have her… the ideas are back."

He smiled—sharp, alive.

No more waiting.

First: proof of pathway—run small tests without committing.

He called Kai2 over, then didn't speak a vow—only simulated it with red stitch: intention-construction without sealing the terms. He pushed red stitch threads as conditions through the fish, watching for rejection, instability, and feedback. Nothing snapped. No recoil. No backlash.

Good.

Next, he grabbed the broken Inverted Spear of Heaven and wound Red Stitch around it—tight, precise, every thread interlocking like circuitry. Visually? Nothing changed.

Energetically?

Different story.

He pushed cursed energy through the stitch, and it slid cleanly into the blade, as if the thread and the metal were a single conduit.

A slow smile split his face.

"Bingo."

It's possible. The Red Stitch can act as a live relay—his own cursed energy traveling down his own circuit into the weapon. That meant embedding a permanent, perfected circuit wasn't just theory—it was execution waiting to happen.

He let out a breath, then stared at Kai2 again.

"The second piece: can you take Flood Maw?"

If he could transfer a technique—even a simple one—then the final fusion would work. And if it worked…

He'd have a blade with:

The Inverted Spear's base (structure, stability).

Kai2 as the living core (energy, responsiveness, adaptive behavior).

Flood Maw is the embedded cursed technique (offense, elemental execution).

A Red Stitch perfected circuit (control, linkability, efficiency).

"I've merged the impossible before," he reminded himself. "The first test I ever did—when Kai got absorbed by me, when I unlocked Red Stitch—what I did then was more impossible than this. Back then I didn't know anything. Now I understand curses, techniques, and binding vows. This isn't madness—it's engineering, cursed engineering!"

His grin widened.

"If this works… I'm making a special-grade cursed tool on the spot."

He sat back down, heart thudding—not with fear, but with anticipation.

"Alright, Kai2… Let's see what you can become."