After climbing down the narrow, steep spiral stair into the next layer, Sophia found that the dungeon’s ecosystem had shifted completely.

  The second floor belonged to Rock Golems—massive stone constructs—larger and far sturdier than the mantises above.

  Their physical defense was terrifying, and their Regeneration was the truly irritating part. Unless you destroyed the Mana Core hidden inside their bodies, they would gather surrounding rubble and rebuild themselves endlessly.

  There weren’t as many of them as on the first floor—

  but their sheer durability turned every push forward into a slow grind.

  Rein, however, showed a different kind of interest.

  After Sophia sliced through two golems with razor-wind magic, Rein immediately dashed in to inspect the broken stone remains. He took a moment to study the structure—then turned to her.

  “I think I’ve found the weakness,” he said. “I’m going to look for a shortcut to the boss. No point wasting mana on unnecessary fights.”

  He held out a small glass vial filled with a clear blue liquid.

  “Here. Drink. Mana recovery.”

  “There’s still more of that?” Sophia took it and drank obediently. “How many bottles did you even bring?”

  Her depleted mana began to refill—warmth spreading through her circuits.

  She glanced at Rein as he calmly pulled out another bottle, this one labeled as a Stamina Potion, from his cloak pocket.

  He didn’t answer.

  He simply patted the cloak—suspiciously flat for something holding that much—then reached in again, pulled out a paper-wrapped sandwich, and tossed one to her.

  Sophia unwrapped it and took a huge bite, eyes narrowing with suspicion.

  “That’s… a Dimensional Storage cloak, isn’t it? A magic storage cloak that can hold basically anything.” She chewed. “Those are rare. Where did you get something like that?”

  “Secret,” Rein said shortly, pulling out his own sandwich.

  He sat down on the shattered head of the golem they’d just killed, using it like a chair in the cold, silent dark.

  Sophia swallowed her last bite, brushed crumbs from her fingers, and shifted restlessly.

  “The duel starts soon up there,” she said. “Aren’t you worried? Not even a little?”

  “What if we don’t make it back in time? You could be declared absent—or Winter will accuse you of running away like a coward!”

  Rein went quiet.

  His gaze turned distant, as if he was turning something over in his mind that Sophia couldn’t reach.

  Instead of answering, he pulled out a strange metal flask from his cloak—along with two small metal cups.

  He set the cups on the cold stone floor.

  Then he poured amber-colored tea, still steaming, into them.

  A gentle fragrance rose from the leaves, cutting cleanly through the dungeon’s damp rot.

  “Good thing,” Rein said casually, handing her a cup. “The other day, when I went through the Kingdom Zone, I stumbled onto a hidden item shop that sold heat-retaining flasks.”

  “I had the cloak shop next door sew an insulated sleeve around it, too—so it’s easier to carry and doesn’t burn your hand.”

  He nodded toward her cup.

  “Now we can drink hot tea and rinse out the awful taste of mana potions. Nice, right?”

  Sophia sipped, still confused—until warmth spread through her chest and she almost nodded along in a trance.

  Then she jerked her head up.

  “Hey! Don’t change the subject! I’m talking about something life-or-death here—the duel!”

  “Ah. Right. The duel.” Rein nodded lazily, then glanced at the surrounding darkness littered with stone giant corpses.

  “I know, Sophia.”

  “But what exactly do you think we can do about it right now?”

  He lifted his tea and took a slow sip—far too calm—before saying, evenly:

  “We deal with what’s in front of us first.”

  “Everything else can wait.”

  He put the cups and the thermos away with smooth efficiency, then rose—his posture shifting into something sharper.

  “Let’s clear the boss of this floor.”

  “After that, we dive down and deal with the one guarding Floor Three.”

  “On the way back, we farm the respawned bosses on Floors One and Two.”

  His head tilted slightly as he calculated.

  “That gets us the cores we need: two B+ cores, and three A-grade cores.”

  He looked at her.

  “With mana density that high, We can substitute those for the standard six B-grade cores. Easily.”

  “And it’ll push your refinement success rate… past a hundred percent.”

  Sophia’s mouth fell open at a plan that sounded downright inhuman.

  “You’re talking about killing six high-rank bosses in one run…” she blurted, “with just two people—in a few hours?!”

  “Do you have any idea how long top-tier adventurer parties spend preparing for a single boss? Months!”

  “They spend months wandering blind because they don’t know the route,” Rein replied mildly.

  “So why would we waste time doing that… when the exit is right in front of us?”

  He turned and walked straight to one side of the stone wall.

  In the dark, his blue eyes flashed—like a precious gem.

  He pressed his palm to the cold surface, feeling for a hidden seam.

  “It should be around here… ah. Found it.”

  He pushed on a stone that looked too smooth.

  Gears hidden inside the wall engaged.

  The stone sank inward—and a massive slab slid aside with a heavy, grinding roar that echoed through the corridor like a giant waking from sleep.

  Rein glanced back at her, a faint smile curving.

  “The shortcut to the boss room is open,” he said lightly.

  “After you.”

  From the map data he’d gathered in The Hub, Rein was confident this dungeon had a shortcut to the boss room on every floor.

  He only needed to pinpoint the exact location.

  The moment they crossed into Floor Two, he activated MiDAR, sweeping the entire level in a silent pulse and reconstructing it into a centimeter-precise three-dimensional model within his vision.

  And eventually—he found what he was looking for.

  This tale has been unlawfully lifted from Royal Road; report any instances of this story if found elsewhere.

  A route hidden behind geometric mechanisms in the stone wall.

  Rein had predicted this from the start.

  If this dungeon had truly been built as a biological weapons research facility, there was no conceivable reason for its creators to waste time hacking their way through the very monsters they had engineered—merely to observe results.

  “It’d be idiotic,” Rein muttered under his breath, leading Sophia onward, “for researchers to get lost in their own lab.”

  They stepped into the boss hall.

  The boss of this floor was a colossal rock golem—towering as tall as a four-story building.

  Its destructive force could pulverize everything into dust in an instant, and its Magic Resistance was shockingly high.

  But to the two of them—the giant looked slow. And full of openings.

  Rein activated Mana Vision, locking onto a deep green concentration point inside the golem’s chest.

  He took the role of decoy, drawing the giant’s attention and kiting it across the hall—

  shouting out the exact coordinates Sophia needed to finish it.

  Rock golems were, by nature, the enemy of mages due to their elemental resistance.

  But Sophia was an exception.

  Her control—blending mana with physical mechanics—was flawless.

  Even back when they first met in the Student Council, Rein had analyzed her Vacuum Blade: it wasn’t “wind” at all.

  It was a sudden, ruthless creation of low pressure—producing a destructive force capable of tearing even obsidian stone at the molecular level.

  Rein slipped past the golem’s massive fist with Haste, agile and precise—

  while above, Sophia gathered mana, forming a gigantic Vacuum Blade nearly ten feet long.

  She launched through the air—

  and snapped her kick, sending that invisible edge straight into the fatal point Rein had called out.

  The result required no embellishment.

  The giant that had moments ago seemed immovable and eternal—

  fractured in a single instant, collapsing into a thunderous avalanche of stone.

  An emerald Monster Core dropped amid the rubble, flawless and unscarred.

  That carrot… Rein thought, watching the flawless dissection with quiet admiration.

  So much power—compressed, refined—wielded with the clinical precision of a surgeon’s scalpel.

  Ten minutes later, the two of them descended to the next floor.

  Sophia quickly realized that Floor Three belonged to Giant Spiders.

  Every square inch was smothered in thick webbing—sticky as the finest glue. If you so much as brushed it, pulling free would cost strength and time in a way that made your teeth grind.

  And worse—these threads could absorb mana.

  They also functioned like signal lines, calling hundreds of spiders to the prey the moment the web was disturbed.

  As they moved carefully through stone corridors slowly veiled in cloudy white silk, Sophia couldn’t help comparing the Rein who had beaten her at the AGMT duel to the Rein walking ahead of her now.

  Something was different.

  The Rein she had faced during AGMT had been a demon—sharp, merciless, burning with the need to prove himself to the world.

  She stole a glance at his back now.

  Back then… he had been on fire.

  Just like her.

  However this Rein felt… changed.

  He still irritated her—still carried that infuriating, arrogant air, still acted like her opinions barely registered.

  But he walked as if someone placed a map right in front of him.

  And somehow—unbelievably—he guided her through hidden routes buried in shadow, avoiding the “web-hell” completely.

  If they’d taken the normal paths, they would have spent dozens of hours fighting nonstop.

  He really is a genius…

  The realization slipped into her mind before she could shut it out.

  They called her a rare prodigy—

  yet beside Rein, she felt like a girl trailing behind an adult who could see through everything. His presence was too “old” for his age. Almost unnatural.

  Outside, he was still the same annoying bastard.

  Inside…

  it felt like someone you could actually trust was hiding there.

  Sophia sealed that conclusion silently in her heart.

  After only half an hour, they reached the central hall of the Third Floor—

  the nest of the Tarantula Spider Queen.

  An eight-legged monstrosity she had previously encountered only in the illustrated margins of high-rank adventurer logs.

  Its legs were sharp like iron spears, capable of punching through stone.

  And the swollen sac beneath its abdomen was ready to spit steel-like silk to bind an enemy at any moment.

  The old plan returned—

  Sophia would lure. Rein would finish.

  But this time, as she drew the spider minions away, Sophia cast Haste on herself.

  With a single tap of her foot, her body blurred—leaving only an afterimage. No spider would ever catch her.

  Because Sophia wanted to see it with her own eyes—how Rein fought a high-rank boss.

  And what she witnessed erased every doubt.

  Rein faced the Spider Queen alone.

  He didn’t cast a single offensive spell.

  Instead, he raised a Magic Shield—a deceptively simple circular barrier, no wider than two feet across.

  It looked ordinary. Almost laughable.

  Yet it received the Spider Queen’s crushing strikes without so much as a tremor—

  as if her legs were slamming into a mountain that would never move.

  But the shock didn’t end there.

  Rein didn’t use the shield only to defend.

  He spun it—once, twice—and the air shrieked under the acceleration.

  Then he released it.

  The shield became a killing discus.

  It cleaved straight through the Tarantula Queen—through the steel-hard silk she commanded—and parted her body with surgical indifference.

  Sophia froze like a statue.

  Her eyes were wide as she stared at the Queen’s severed corpse—

  killed by a “shield.”

  The destructive force rivaled her own Vacuum Blade—

  the technique she had polished to perfection.

  And he had unleashed it with the ease of someone tossing a pebble into a pond.

  It was far beyond a Troposphere Master-tier.

  “H-How…? Where did you get that spell—no, that way of using a spell?”

  Sophia’s voice cracked as she fought to gather her thoughts.

  Rein turned slowly.

  The blue light in his eyes narrowed slightly.

  Then he lifted a finger to the iron mask and tapped the lips—lightly.

  “Secret,” he replied lightly.

  “And some things are better left that way.”

  “Secret again!” Sophia snapped, folding her arms, glaring at him. “Honestly, I’m starting to wonder if you’re a Shapeshifter—or something worse pretending to be human!”

  Rein didn’t answer.

  He simply dropped onto one of the Spider Queen’s still-warm legs, uncorked a Mana Potion, and chugged it in one go.

  His face immediately twisted into something ugly as hell.

  The taste was beyond horrific.

  “Oookay… I take it back.” Sophia burst out laughing at the sight. “A Shapeshifter wouldn’t make a face that disgusting drinking a mana potion.”

  “You’re Rein. The real one.”

  Half an hour later, Rein and Sophia returned to wait for the same “unlucky victim” again.

  The giant golem boss, barely respawned for five minutes, was smashed back into rubble by Sophia.

  And the blind mantis king was decapitated a second time the moment it returned.

  Even with five high-grade Monster Cores in her hands, Sophia still felt like she was dreaming.

  Two students.

  B+ and A-rank bosses.

  A handful of hours.

  And an outcome that would have taken elite parties months.

  This is a revolution…

  Rein’s method wasn’t just efficient—

  it tore up every textbook she’d ever believed in.

  When they returned to The Hub, the hidden laboratory, Rein didn’t waste a second.

  He began constructing a new Mana Refinement Ring.

  He placed the five cores at the ring’s center, then nodded for Sophia to step into position.

  “Wait…” Sophia’s voice trembled slightly. Anxiety gnawed at her chest. The cores in her reach were worth millions of AC—yet Rein treated them like roadside pebbles.

  “You’re sure?” she asked quietly.

  “Have you… ever done this before?”

  “Relax,” Rein said evenly.

  “You’re my first live test subject.”

  “…Huh?”

  Sophia’s eyes went wide.

  “WHAT!? You mean this is your first time!?”

  “Hey.” Rein frowned. “Don’t shout. If someone hears you, they’ll get the wrong idea.”

  “Who’s going to hear us!? This is an underground dungeon, you idiot!” Sophia kept yelling—

  but at that exact moment, the ring beneath her feet began to glow.

  Their argument died instantly.

  “Clench your teeth,” Rein said, voice hardening. “We’re starting the refinement—now.”

  With his left hand, Rein activated the primary ring.

  Multiple layered rings ignited and began rotating—counterclockwise, alternating in rhythm.

  The five Monster Cores melted, turning into pure mana fluid.

  Sophia’s body lifted from the ground as if gravity itself had loosened its grip—

  and then the current struck.

  Colossal. Relentless.

  Mana roared through her circuits like a storm tearing through a city.

  [LIZ: Refinement success rate… 47%… 49%… 50%. We’ve reached the maximum limit of a single-layer ring, Rein!]

  “Proceed to the next step!”

  Rein clenched his jaw. Sweat beaded across his face.

  Then, slowly, he raised his other hand.

  What he was about to do consumed a monstrous amount of mana—and shattered the limits of human sense.

  With his left hand sustaining the primary ring,

  Rein raised his right—

  and began constructing a second Mana Refinement Ring from nothing.

  This was Dual-Hand Casting—

  a discipline that even high-tier mages struggled to execute without tearing their own mana circuits apart.

  And Rein layered it calmly over the first.

  These entries expand the lore and mechanics introduced in this chapter.

  Completely optional—read only if you enjoy diving deeper into the system.

  Artifacts and Items

  Dimensional Storage Cloak

  A rare magical item capable of storing a large number of items despite appearing physically flat or empty. Rein uses one to carry potions, food, and even a thermos of hot tea. The internal space operates on pocket-dimension logic, functioning like a portable sub-reality for item containment.

  Mana Potion

  A standard alchemical item used to restore a mage’s internal mana reserves. Rein uses multiple during the dungeon run. Though effective, it is noted to taste absolutely horrible.

  Stamina Potion

  An alchemical brew designed to restore physical endurance and reduce fatigue. Used alongside mana potions to sustain longer battles.

  Monster Core (B+ / A-Grade)

  Crystalline cores extracted from high-rank monsters. Serve as power sources for enchantments, mana refinement, or high-grade crafting. In this chapter, Rein plans to use 2 B+ cores and 3 A-grade cores to exceed the mana refinement threshold.

  Heat-Retaining Flask

  A practical invention found in a hidden item shop, capable of keeping liquids hot for long periods. Used by Rein to bring tea into the dungeon, emphasizing his attention to both comfort and morale.

  Magic & Spell Techniques

  Mana Refinement Ring (Dual-Layered)

  A highly complex magical construct designed to channel Monster Cores into the mage’s mana circuits, enhancing their density and purity. Rein’s version uses a two-layer setup to push beyond conventional limits, multiplying the power and risk involved. Requires Dual-Hand Casting.

  Dual-Hand Casting

  The act of simultaneously constructing and sustaining two separate magic circles or spells with each hand. Extremely rare and dangerous, as it requires perfect control over mana flow to avoid overload or internal injury. Rein executes it to stabilize the dual-ring refinement process for Sophia.

  Concept

  Shortcut Mechanism

  Hidden mechanisms built into the dungeon’s design, presumably by researchers to avoid the monsters they created. Rein locates and activates these to skip unnecessary battles.

  Monster

  Tarantula Spider Queen

  A boss-level monster on Floor Three of the dungeon. Massive, armored, and capable of silk attacks strong enough to penetrate stone. Slain by Rein using his weaponized shield technique.

  Colossal Rock Golem

  Boss Monster on the Second Floor of the dungeon. A titanic golem forged from densely packed stone, clay, and mana-rich sediment. Standing over forty feet tall, the Colossal Rock Golem acts as the last obstacle of the dungeon’s second floor. It possesses massive physical strength, near-impervious defense, and devastating shockwave attacks that pulverize everything in a wide radius.

  Sophia uses Vacuum Blade to slice through its dense limbs, while Rein exploits timing and structural weaknesses to finish the fight.