Underground Lab — Subterranean Levels Beneath Aokusa Forest
The entrance closed behind them with a wet shhhlick.
Mirko winced, the pain in her side flaring again. She bit it back. The others didn't need to see it.
Bioluminescent tendrils lined the ceiling, glowing faint red. The walls weren't built—they'd grown. Flesh fused with decayed tech, veins snaking into machinery. The floor squelched under their boots.
"This isn't a lab," Rock Lock muttered. "It's some sort of creature" he said with a look of disgust.
Volt stepped closer to a growth pod on the wall—inside, a half-formed humanoid thrashed weakly against the membrane. Its eye opened. Red.
He stumbled back. "These things aren't human anymore…"
"They never were," Mirko said. "Not once Mazoku got to them."
Suddenly, the corridor shifted. The walls spasmed—alive, aware. Something knew they were inside.
Mandalay stiffened. "Incoming."
From the far end of the corridor, three mutated guards emerged. Their bodies were stretched, broken into impossible shapes. One's spine bent backward like a scorpion's tail. Another's jaw split wide, revealing rows of teeth too deep.
Mirko stepped forward, voice low and firm.
"No quirks. No noise. This is a hit-and-fade."
She leapt first.
Bone cracked beneath her foot as she slammed the first mutant into the wall. Rock Lock trapped the second by fusing the floor around its limbs. Volt surged, frying the nervous system of the third with a burst of concentrated voltage.
Silence returned.
Then the walls… moaned.
Something deeper had felt that.
Mirko nodded toward the elevator-shaped growth ahead. "Let's go. Mazoku's at the bottom. So is the Rush source."
They moved fast, deeper, past tanks of failed experiments and twitching corpses. And then—
They reached the central chamber.
A massive heart-like organ throbbed in the center, suspended by tendons, dripping Scarlet Rush into living veins below. Around it, tubes pumped glowing red fluid into a wall of pods—hundreds of them.
Rock Lock stared. "This… this is production. He's farming these creatures ."
Mirko stepped forward, baring her teeth.
"Then let's kill the crop."
———————-
Back at U.A. — Hero Arena, 20 Minutes into the Attack
A containment perimeter had been set. Students evacuated. The mutated infected had either been subdued or neutralized.
But the air was still heavy with unease.
Behind closed doors in the Hero Commission's makeshift war room, Principal Nezu, Aizawa, Tsukauchi, and several top heroes gathered around a table. A huge screen displayed a live-feed of data, medical scans, and surveillance.
"I ran facial recognition on one of the infected," Tsukauchi said grimly. "Koji Sakamura. Quirk-enhancement forum regular. Vanished a week ago."
"And the injection marks?" Aizawa asked.
"Confirmed. Scarlet Rush."
Ryukyu crossed her arms. "They weren't just test subjects. They were placed here. Deliberately."
Midnight frowned. "What for? The festival was full of kids, heroes, media—too risky for just a drug demo."
"Exactly," Nezu murmured. "It wasn't about chaos. It was about making a statement."
Tsukauchi tapped the tablet.
"And here's the worst part—we've traced the formula. Scarlet Rush includes synthesized Quirk DNA from five registered heroes. Stolen DNA."
A long silence.
Aizawa's eyes narrowed. "This was a raid on the future. The message is clear: he can make monsters out of anyone."
Nezu nodded slowly.
"We need to start preparing for societal impact. If people think quirk use leads to mutation…"
"They'll panic," Hawks said from the doorway. His wings were half-burned from earlier. "And worse… some might want the power. Even knowing the risk."
A slow realization spread through the room.
This wasn't just a bio-weapon.
It was a temptation.
——————
Underground maze-
No doors. No exits. Only the quiet thrum of pulsing veins lining the bone-like architecture. The air was thick with the sweet-metallic scent of Scarlet Rush, seeping from the very walls like humidity. It clung to the skin. Invaded the lungs.
Mirko stood at the front of the team—swaying slightly.
Her arm still throbbed. Her side ached. But none of that compared to the burn—that damn itch just beneath her skin. A hunger. A need. She clenched her fists hard enough that her nails bit into her palms.
"Mirko?" Mandalay whispered behind her.
"I'm fine," she spat back, though her voice came out raw and low. Too low.
They were deep underground now. This far in, even GPS failed. And the deeper they went, the more reality felt… wrong. Gravity was heavier. Sound bent strangely. And the walls—they breathed.
At the far end of the chamber, Mazoku stood atop a risen mass of muscle and bone, his eyes glowing faintly red, robes trailing like shadows. Beside him knelt Aika, quiet, her black hair fluttering even though there was no wind.
"You came," Mazoku said, his voice smooth and full of terrible warmth. "I was hoping you would."
"Cut the monologue," Mirko growled. "You're done."
Mazoku tilted his head. "Are you sure? I always thought they had a certain appeal maybe this is just a tough crowd."
Aika nodded her head with a blank look on her face.
Mirko looked around turning back to Mazoku.
Her eye twitched. The Scarlet Rush called out louder here. It was like she could feel it crawling through her bloodstream, reawakening. Her muscles felt too light. Her pupils dilated.
He took a step forward.
"I could give it to you freely this time," he said. "No pain. No needles. Just pleasure."
Mirko lunged—
—and stopped.
Her foot hovered just above the ground. She stood frozen in mid-air, a sudden tremor locking her limbs. Her eyes widened. No… not now…
Mazoku smiled softly. "You feel it, don't you? The link between us now. The resonance. You're already mine in part."
"She's not!" Pixie-Bob shouted, launching a volley of sharpened rock projectiles. They arced like bullets.
Aika's paper danced mid-air, slicing through the rock like silk. She raised her hand, and a spiral of paper daggers spun toward them. Ragdoll shoved Mandalay aside just in time.
Tigress roared and bolted forward, claws out. "I'll carve that grin off your face!"
Mazoku didn't flinch.
With a flick of his wrist, tendrils of muscle burst from the ground and slammed Tigress mid-leap, pinning her against the wall.
"Always so dramatic," he muttered.
Mirko forced herself to move. Her muscles trembled under her own command. Her heart was screaming. Everything felt too fast, too loud.
This is what withdrawal feels like, she thought. This bastard—he designed it that way.
Mazoku watched her. "You're not here to kill me," he said. "You're here because you want more."
"Shut up!"
She leapt. This time her legs obeyed.
Mid-air, she twisted and smashed her good leg toward his head, but Mazoku barely moved—his arm shifted, warping unnaturally as he blocked the kick.
The impact shook the chamber. But he didn't budge.
"You could be perfect," he whispered. "But you're still clinging to the lie of heroism."
He shoved her back like she weighed nothing.
Mirko slammed into a pillar, coughing blood.
Behind her, Mandalay screamed something. Pixie-Bob was trying to free Tigress. Ragdoll had taken a hit and was bleeding from the forehead. The team was falling apart.
Mirko staggered to her feet.
"Even now," Mazoku said gently, "I can make the pain go away."
"Good," Mirko rasped, and smiled through bloody teeth. "I like pain."
She charged again.
————
U.A. High — Underground Strategy Chamber
"Mirko's team's gone dark," Aizawa muttered, staring at the blinking tracker on the screen. "Last signal was 11 minutes ago."
Nezu's face was unreadable.
In the corner, All Might stood in shadow. He hadn't spoken in ten minutes.
A hologram of the Scarlet Rush molecule flickered in front of them—complex, shifting, organic in ways it shouldn't be. Not just a drug. A virus. Alive. Growing.
"This is spreading fast," Nezu said. "Osaka, Shibuya, now even Kirisaki City. We're chasing shadows."
All Might looked up, finally. "Then we stop chasing."
They turned to him.
"We go in," he said. "Full force. Commission-sanctioned or not."
"Into the forest?" Aizawa asked.
"No," Nezu said quietly. "We go beneath it."