The service duct smelled of metal and dust as the four survivors pressed onward, hearts pounding in unison. Slim beams of waning daylight filtered through the grated vents overhead, casting trembling patterns across their faces. Each step felt like a descent into a deeper abyss—not just beneath Haeryun Academy's storied corridors, but into the unknown that had torn their world apart.
Min‑woo led the way, his athletic frame contorting to fit the narrow passage. Every scrape of his jacket against the steel walls echoed like a gunshot. Behind him, Seo‑yeon gripped her dagger hilt, knuckles white, eyes sharp as a hawk's. Jae‑hyun clutched his leather satchel, mind racing through contingency plans. Ha‑neul brought up the rear, holo‑pad clasped to her chest, guilt and determination flickering in her gaze.
They crept toward the maintenance stairwell at the duct's end—an emergency exit rumored to open into the faculty quarters. But as they approached, a low, anguished moan drifted up from the labyrinth below, freezing them mid‑crawl.
"Zombies," whispered Seo‑yeon, voice hushed yet electric. "Below us."
Min‑woo paused, listening. The moan swelled into a chorus of tortured lamentations, punctuated by metallic clanks—perhaps tools dropped by panicked custodians turned prey. He flexed his fingers around the duct's edge. "We can't let them surround us."
Jae‑hyun exhaled slowly. "We need to create noise elsewhere to draw them away." His mind, ever the strategist, sketched a plan in fractions of a second. "Ha‑neul, do you still have battery power on your holo‑pad?"
Her augmented lenses flickered as she tapped the side of the device. "Twenty percent," she replied. "But I can route a signal through the academy's low‑frequency speakers in the east wing. It'll buy us two minutes at best."
Seo‑yeon nodded. "Two minutes is enough. Min‑woo, you and I will detour to the service shaft landing and trigger the alarm. Jae‑hyun and Ha‑neul head to security—find a map of the outbreak zones." She drew a steadying breath. "Divide and conquer."
A beat of silence, then four nods. They split: Min‑woo and Seo‑yeon slid silently back into the corridor, while Jae‑hyun and Ha‑neul continued toward the security hub through a parallel tunnel.
Min‑woo and Seo‑yeon emerged into a narrow supply corridor lined with dusty crates. The stench of damp wood and stale air was overwhelming. With each step, Min‑woo kept his free hand on Seo‑yeon's elbow—an unspoken reassurance. When they reached the service shaft's landing, he yanked the lever marked "Emergency Signal."
In the east wing, hidden speakers crackled to life with a bone‑chilling wail. It pierced the air like an alarm of war. Min‑woo and Seo‑yeon vanished back into the shadows just as the undead below clamored toward the sound, their hungry groans echoing upward.
Meanwhile, deeper beneath the academy, Jae‑hyun and Ha‑neul arrived at a reinforced door stamped "Security Control." Jae‑hyun's fingers danced across the biometric keypad, overriding lockdown sequences with the authority of his mentor's credentials. The door hissed open.
Inside, rows of monitors displayed flickering CCTV feeds—corridors in chaos, students fleeing, labs ablaze with eerie green flames. A half‑burned map of Haeryun's lowest levels hung on a corkboard beside the screens, corridors marked in red and blue. Jae‑hyun traced a route with a gloved fingertip.
"These corridors lead to the central power grid," he murmured. "If we can reestablish stable energy, we might isolate the outbreak to a single zone."
Ha‑neul scanned the data logs. "The first infection was here, in Lab 3B, at 3:14 AM. My lab." Her voice quavered. "I released the catalyst as a test… I never meant this to spread."
Jae‑hyun placed a reassuring hand on her shoulder. "We'll fix this," he vowed. "We'll contain every sample, reverse what's been done."
Her eyes met his—frail, luminous beneath the flickering screens. "Promise me," she whispered, "no more lives lost because of me."
He nodded. "I promise."
Above them, Min‑woo and Seo‑yeon navigated back to the duct junction, every corridor birthing new horrors. A wailing figure lunged from a corner; Seo‑yeon slashed its forearm, and Min‑woo finished it with a swift elbow to the jaw. They moved on, adrenaline their ally, until the distant pulsing of the alarm signaled success.
Pausing at the junction, Seo‑yeon's chest heaved. "They're converging on the service docks. We still have time."
Min‑woo brushed a petal from her hair—soft as silk against steel. His voice was low but earnest. "We will get through this… together."
In that moment, beneath flickering emergency lights, their eyes locked. It was a promise and a confession entwined—a spark that neither the undead nor the catastrophe could extinguish.
Elsewhere, Jae‑hyun and Ha‑neul hacked the main console. With a flurry of commands, power grids rerouted, doors sealed, and security shutters descended across infected wings. A hush fell over the control room as screens went dark one by one, isolating the outbreak to Lab 3B—where the green‑flamed chaos had begun.
Ha‑neul let out a shaky breath. "It's done."
Jae‑hyun's jaw tightened. "Now we retrieve the samples." He tapped the screen to highlight an underground repository marked in blue. "The vault's here—in the subbasement."
Ha‑neul's eyes widened. "That's beneath the old archives. We'll need the master key."
Jae‑hyun reached into his satchel and withdrew the encrypted USB drive. "My discovery isn't just math," he said softly. "It holds the override codes to every system in Haeryun—if we can decrypt it, we can open the vault."
Her hand closed over his. "Then let's decrypt them—now."
They regrouped at the duct junction—four souls drawn back together by peril and purpose. Outside, the academy trembled with distant blasts and muffled screams. Above them, cherry blossoms drifted down empty corridors, their fragility a cruel contrast to the carnage.
Seo‑yeon sheathed her dagger. "Are we all ready?"
Min‑woo cracked his knuckles, smile fierce. "Born ready."
Ha‑neul activated her holo‑pad, the screen glowing like a second heartbeat. "Decrypt sequence starting… now."
Jae‑hyun watched the progress bar climb, every percent a step closer to salvation—or doom. In the cramped darkness, their shoulders brushed, a quartet bound by secrets, guilt, and an unspoken hope that love might still bloom in the ruins.
Behind them, Lab 3B lay sealed—its horrors locked away for now. Ahead, the vault of Haeryun's darkest secrets awaited.
And somewhere, in the silent hum of the academy's buried passages, the final catalyst stirred, aching for release.
The decryption bar trembled at ninety‑five percent as the hum of distant alarms droned through the duct. Ha‑neul's fingers flew over the holo‑pad, sweat beading at her temples.
"Almost there…" she whispered.
Below them, the muffled thuds of pounding feet grew louder—the undead, drawn by the siren's false promise of prey. The metal grate above their heads rattled.
Min‑woo pressed his back against the duct wall. "We need to move—now!"
With a final chime, the holo‑pad lit green. Jae‑hyun snatched it, heart pounding. "Got it!" He tapped the drive into his satchel and rose. "The vault's two corridors east, then down a service stair. Follow me."
They slipped from the duct into a narrow maintenance hall. Deadbolts slid shut behind them, and the grate clanged shut overhead. Seo‑yeon's dagger traced impatient patterns across her palm.
"Next stop: the subbasement archives."
Jae‑hyun unfolded the academy blueprint, projecting it in ghostly blue lines. "Here—through that door, and then left at the junction. The vault door should be marked with the Haeryun crest."
Ha‑neul swallowed. "Let's just hope the override codes work on the old mechanical locks."
They sprinted down the hallway, rounding corners two at a time. Fluorescent lights flickered overhead, and every shadow felt alive. A low groan echoed from around the bend.
Seo‑yeon held up a finger. "Zombies." She pressed herself flat against the wall, clasping Min‑woo's sleeve. "We'll have to sneak past."
Min‑woo nodded. "On three." He and Seo‑yeon inched forward, stepping over broken floor tiles. A gaunt hand snaked through a broken window frame—black fingernails scraping metal. A creature's hollow eyes fixed on them.
Seo‑yeon froze. The zombie's jaw hung loose, tongue lolling. Its rasping breath misted in the cold air.
Min‑woo slipped an arm around her waist and in a single motion pulled her backward. They slipped past as the creature lunged, its clawed hand slamming into empty air. Heartbeats later, they were around the corner, and Seo‑yeon let out a breath she'd held.
"Close one," she murmured.
Behind them, Jae‑hyun and Ha‑neul encountered no such resistance—few had ventured this deep in the panic. They reached a weathered steel door embossed with the academy crest. A mechanical dial lock sat at its center.
Jae‑hyun pulled the decrypted drive from his satchel and inserted it into a small port beside the dial. Gears clicked. The dial spun, numbers falling into place.
"Vault override accepted," a calm, digitized voice intoned.
Ha‑neul exhaled. "You did it."
But before Jae‑hyun could turn the handle, the door shuddered under a brutal impact. The undead on the other side had discovered them.
"Battle stations!" Min‑woo's voice crackled in Jae‑hyun's earpiece.
On the other side of the corridor, Seo‑yeon stepped forward, dagger raised. Min‑woo caught her wrist. "Let me," he said, and with one fluid motion scooped her into his arms. He dashed toward the vault's side panel and slammed his shoulder into it. Metal groaned but held.
Inside the vault, the four tumbled in together, slamming the heavy door shut. The lock engaged with a pneumatic hiss, plunging them into darkness. Emergency red lights glowed to life.
Ha‑neul's holo‑pad illuminated the chamber. Rows of reinforced glass cases displayed serum vials—emerald liquid quivering within. At the far end, metal cabinets held stacks of confidential files.
Seo‑yeon leaned against Min‑woo's chest, breath still shaking. "Is everyone all right?"
Jae‑hyun wiped sweat from his brow. "We're safe—for now."
But Ha‑neul's gaze was already on the cabinets. She tore open the top drawer and extracted a file stamped "Project Rebirth." Her hands trembled as she flipped through pages of schematics, cell‑regeneration charts, and untested protocols.
"This is it…" she breathed. "My research… and all the hidden tests."
A sudden crash rattled the vault door. The undead outside battered it with inhuman strength.
Seo‑yeon drew her dagger again, eyes fierce. "They're not giving up."
Min‑woo squared his shoulders. "Then neither are we."
Jae‑hyun studied the files. "There's a counter‑serum formula here—an inhibitor to reverse the catalyst's effects. But it needs to be synthesized using lab equipment back in 3B."
Ha‑neul's voice caught. "You want to go back?"
He met her eyes. "We can't leave anyone alive out there to suffer. Not after what happened." He gestured at the vials. "We take what we need, then head back. We finish this—together."
For a heartbeat, they all simply stared at the rows of glass bottles, the weight of their task settling in. Then Seo‑yeon stepped forward, placing a hand over Ha‑neul's. "We'll do it," she vowed. "Side by side."
The vault door groaned again under the onslaught, but inside, the four stood united—two couples bound by crisis, and a promise heavier than steel: they would confront the darkness they had unleashed, or die trying.
Above them, the dead clawed at the walls. Below, the secrets of life and death waited to be wielded.
And in that electric stillness, their real journey had only just begun.