The sky over Japan felt different now—thicker, gray with the smog of hidden DSC factories and the perpetual tension of a stalemate.
Ren sat in the "Omega Sanctum," a deeper, more fortified layer of the Aegis Wing. He had grown; his ice-blue hair was now a sharp, professional cut, and his crystal-blue eyes were perpetually framed by the HUD-glow of his latest goggles. He no longer looked like a fragile child, but a tired commander.
Muzan, driven by a paranoia that had reached a fever pitch, had sacrificed thousands of low-level demons just to understand Ren's weapons.
The demons had adapted. They no longer moved in predictable patterns. Muzan had used his blood to engineer "Hardened Carapace" demons—creatures whose skin had a high silicon content to reflect the Apollo Flash. They developed "Seismic Senses" to detect Ren's underground sensors and used their own flesh to create "Biological Jamming" organs that hummed at the same frequency as the Aoki-Radio, creating static in the Slayers' ears.
Muzan himself had become an enigma. He had moved the Infinity Castle into a spatial pocket that even A.I.D.A. couldn't pinpoint. He was no longer just a monster; he was a biological architect matching Ren move for move.
TP Spent: 40,000 (Accumulated over the 2-year skip)
Ren entered the Lab. The machinery was no longer brass and steam; it was sleek, cold, and hummed with a low-frequency power. He had spent two years perfecting the "Aoki-Pattern Nichirin Blade."
Technical Document: Aoki-Pattern Mark IV
The Problem: Traditional forging was too slow. Hand-folded steel couldn't keep up with the new, hardened demons.
The Solution: Molecular Vibration Forging. Ren developed a system where the Sword Smith Village used high-frequency resonance to "settle" the Nichirin molecules.
The Result: Mass-produced blades that were 30% lighter and possessed a "Chain-Serrated" edge. When a Slayer swung, the blade vibrated at 20,000 cycles per second, allowing it to saw through even the most "hardened" demon skin like it was warm butter.
Ren delivered the blueprints to the Sword Smith Village via a high-speed, automated drone convoy. The village had been transformed into a sprawling industrial forge, churning out weapons that would have made their ancestors weep with both pride and terror.
Despite the new blades and the mass-produced "Sun-Lead" rifles, Ren felt the weight of the stalemate. He knew Muzan was waiting for him to slip up.
"A.I.D.A.," Ren's voice was raspy from lack of sleep. "Logically, we are fighting a war of attrition. At this rate, we will run out of Slayers before Muzan runs out of blood. I need a 'Zero-Point' solution."
"REN-SAMA," the computer responded, its voice now possessing a hauntingly human cadence. "YOU ARE REFERRING TO THE THERMOBARIC WISTERIA PROXY. THE 'MOTHER OF ALL DEMON BOMBS' (MOADB)."
Ren stared at the blueprint on his screen. It was a weapon of mass destruction designed to aerosolize concentrated Wisteria toxins using a high-temperature blast. It wouldn't just kill a demon; it would turn a 5-kilometer radius into a dead zone for demon cells for a hundred years.
"It's... it's a bit much, isn't it?" Ren whispered, his hand hovering over the 'Confirm Purchase' button on the System.
"IT IS LOGICAL," A.I.D.A. replied. "BUT THE MATERIALS REQUIRED—REACTIVE URALITE AND REFINED SUN-CRYSTAL—ARE NOT IN THE SYSTEM SHOP. YOU MUST LOCATE THEM IN THE REAL WORLD."
The oppression of the era reached a breaking point when Muzan sent Upper Moon One, Kokushibo, to destroy the Sword Smith Village and halt Ren's production line.
Ren didn't just hear about the attack; he saw it through the eyes of a thousand drones. He saw the legendary swordsman cutting through his automated turrets as if they were made of paper.
"All Hashira, divert to Sector 7!" Ren commanded through the Aoki-Radio. "I am deploying the Vanguard Unit 02."
Ren didn't wait. He stepped into a new, larger mech—the "Aoki-Dreadnought." It was a walking tank, plated in Nichirin-steel and armed with dual "Gravity-Cannons."
He arrived at the village as the sky turned blood-red. Kokushibo stood amidst the burning forges, his six eyes tracking the massive machine's arrival.
"A metal shell..." Kokushibo's voice echoed, cold and ancient. "You seek to hide your weakness behind iron, child."
"Logically," Ren's voice came through the external speakers, steady and cold, "iron is more reliable than flesh."
The battle was a tectonic shift. Kokushibo's Moon Breathing shattered the village's stone walls, while Ren's Gravity-Cannons warped the very air, trying to crush the demon's internal organs. It wasn't a duel; it was a collision of eras. Ren used Calculus Breathing: Seventh Form (Orbital Decay), using the mech's thrusters to spin in a lethal circle, creating a vacuum that pulled Kokushibo toward a 50-barrel Nichirin volley.
The demon was forced to retreat—not because he was defeated, but because the "cost-benefit analysis" favored survival. Ren had successfully protected the forge, but at the cost of 40% of the village's infrastructure.
After the battle, Ren stepped out of the smoking mech. He was covered in soot, his hands shaking from the feedback of the gravity-cannons.
The Hashira gathered around him. They didn't see a child anymore; they saw a weary general. Shinobu walked up to him, her own haori singed. She didn't hug him this time. She simply placed a warm hand on his shoulder and handed him a bottle of water.
"You're pushing yourself too hard, Ren-kun," she said, her voice filled with a quiet, heavy concern. "The Master is worried. We are all worried."
Ren looked at her. He wanted to explain the math—that if he stopped for even a day, the demons' adaptation rate would surpass their defenses. But as he looked into her eyes, his "Logic Brain" finally short-circuited under the weight of two years of repressed emotion.
"The... the structural damage to the village... is approximately..."
His face didn't just turn red; it turned a pale, sickly pink as he realized he was standing in the middle of a burning village, being comforted by the person who most distracted his calculations.
"I... I need to calibrate... the... the water..."
Ren's eyes rolled back. He didn't do a backflip or a dramatic slide. He simply leaned forward and fell asleep (and fainted) directly against Shinobu's shoulder, his small body finally giving in to the exhaustion of being the world's only hope.
"He's finally quiet," Sanemi muttered, putting away his blade. "Took a god-level demon and a burning village to make the brat take a nap."
Ren locked himself in the "Deep Core" of the Aegis Wing. The walls were lined with pressurized glass vats containing fragments of Upper Moon flesh harvested from the Siege of the Forge. In the center sat a Molecular Sequencer—a machine that shouldn't exist for another century, humming with a soft, rhythmic pulse.
"A.I.D.A.," Ren said, his voice echoing in the sterile room. "Compare the mitochondrial DNA of the Akaza specimen with the records of the Heian-era 'Doctor' who originally treated Muzan."
"ANALYZING..." A.I.D.A. replied. A complex, double-helix structure projected into the air, glowing a sickly crimson.
"REN-SAMA, THE MUZAN-CELL IS NOT MERELY A MUTATION. IT IS A PARASITIC ORGANISM THAT REQUIRES A SPECIFIC CHEMICAL CATALYST TO STABILIZE. WITHOUT IT, THE HOST SUFFERS FROM PHOTO-SENSITIVE CELLULAR COLLAPSE—SUNLIGHT SICKNESS."
Ren adjusted his goggles. "The Blue Spider Lily. The 'Doctor' used it as a medicine for Muzan's terminal illness, but he died before the treatment was finished. Logically, the flower contains the missing link that allows a body to handle extreme cellular regeneration without the side effect of being vaporized by UV rays."
TP Spent: 15,000 (Earned from the Forge Defense & Data Analysis)
Ren entered the Lab. He wasn't building a bomb this time. He was building a Biological Trojan Horse.
Technical Complexity: The "Aoki-Anti-Muzan" Virus (AMV-01)
The Concept: If Muzan's cells are a parasite, they can be "deceived."
The Execution: Using the 15,000 TP, Ren created a synthetic enzyme that mimics the properties of the Blue Spider Lily but with a "Delayed Lethality" trigger.
The Result: Instead of curing the sunlight weakness, this enzyme attaches to a demon's cells and, upon exposure to a specific frequency of Aoki-Radio waves, it forces the cells to undergo "Hyper-Aging."
Ren stared at the tiny vial of clear liquid. This wasn't just medicine; it was a way to force a demon back into being a mortal human—or to age them 10,000 years in ten seconds.
To test the virus, Ren needed a live subject of high quality. A.I.D.A. flagged a surge in demonic activity in the Mount Natagumo region.
"A.I.D.A., deploy the Vanguard Unit 03: 'Arachne' Edition," Ren commanded.
He didn't go with the Hashira. He went alone, cloaked in the Void-Silk Stealth Field. He watched through a drone feed as a group of lower-ranked Slayers were being toyed with by the "Spider Family."
Ren landed in the center of the forest. The "Father Spider" demon, a hulking beast with a literal house on its back, roared at the small, metal-clad boy.
"Calculation," Ren whispered, engaging Calculus Breathing: Ninth Form (Probability Strike).
The Vanguard suit's arm didn't fire a bullet. It fired a Pneumatic Harpoon coated in the AMV-01 virus. The harpoon pierced the Father Spider's chest.
"A toy..." the demon mocked, pulling the spear out. "I feel... nothing."
"Wait for it," Ren said coldly. He pressed a button on his wrist-link. "A.I.D.A., broadcast the 'Requiem' frequency."
The Aoki-Radio towers across the region hummed. The demon froze. His skin didn't burn; it wrinkled. His hair turned white. His massive muscles withered into thin, brittle strings. In less than thirty seconds, the "immortal" demon had become a frail, elderly man-creature that could barely lift its own head.
"The secret is time," Ren said, walking toward the collapsing demon. "You aren't gods. You're just accidents."
The success of the virus was a turning point, but it revealed a terrifying truth. A.I.D.A. processed the data from the Mount Natagumo test and produced a horrifying projection.
"WARNING: MUZAN KIBUTSUJI HAS SENSED THE VIRUS. LOGICAL PROJECTION SUGGESTS HE WILL NOW ATTEMPT TO CONSUME THE 'ARCHITECT' TO INCORPORATE THE STABILIZING AGENT INTO HIS OWN DNA."
Ren realized he had accidentally given Muzan the "Blueprints" to his own perfection. If Muzan captured Ren, he could reverse-engineer the virus to finally conquer the sun.
Ren knew he couldn't wait for the Infinity Castle to find him. He had to build the Mass Destruction Weapon he had envisioned—not just a bomb, but a "Sun-Generator".
Using the 12,000 TP he had left and the rare materials gathered from the Mount Natagumo raid, Ren began construction on Project: AMATERASU.
It was a satellite-relay system that used the Aoki-Radio network to create a "Cylinder of Light." If triggered, it would focus the sunlight of the entire hemisphere into a single, square-kilometer area, even at midnight.
As Ren finished the final soldering on the Amaterasu Controller, the door to his sanctum slid open. It was Kanae and Shinobu. They looked at the boy, who was now surrounded by screens showing genetic sequences and satellite trajectories.
"Ren-kun," Kanae said, her voice filled with a sadness that bypassed his logic. "You're not sleeping. You're barely breathing. You're becoming a machine."
She walked over and gently took the soldering iron from his hand. Ren tried to pull away, his "Social Defense" flaring up.
"The... the synchronization of the mirrors... is at 99.8%... I cannot... stop..."
Shinobu stepped in front of him, blocking his view of the monitors. She leaned down, her face inches from his, and whispered, "The world won't end if you take a breath, Ren. But you will."
She reached out and wiped a smudge of oil from his cheek with her thumb.
Ren's "Logic Brain" hit a Fatal Exception.
Fact 1: The Sun-Generator is nearly complete.
Fact 2: Muzan is coming.
Fact 3: Two Hashira are currently performing 'Emotional Maintenance' on me.
Ren's face went from the metallic gray of his lab to a blinding, supernova crimson. His "Aoki-Skin" suit started to vent emergency steam from the neck.
"I... the thermal conductivity... of your... hands..."
Ren's eyes rolled back. He didn't just faint; he did a slow, dizzy pirouette and landed perfectly in a pile of discarded blueprints, snoring softly as his brain finally forced a "Hard Reset."
"At least he's cute when he's not inventing doomsday weapons," Shinobu sighed, covering him with her haori.