Sophia froze.

  She stared at the boy as if he’d just told a joke too absurd to be real—then a smile slipped out, and it turned into a soft, breathy laugh in her throat.

  “You really never stop messing around, do you…?” she said, shaking her head. “Breaking through the bottleneck? Do you even know how many mages—tens of thousands—spend their entire lives trapped at that tier?”

  Yet her pulse began to trip over itself.

  Because Rein’s eyes didn’t carry the faintest trace of humor.

  “No,” Rein answered, his voice low and steady. “I’m serious.”

  He tapped the stack of documents on the table.

  “While you were sleeping like the dead out there, I was working. I spent the entire night studying these.”

  Hey, idiot—Sophia protested silently.

  I was exhausted. I wasn’t “sleeping like the dead.”

  Rein’s fingertip knocked against an ancient parchment in a slow rhythm, as if emphasizing every line carved into it.

  “It’s a little strange, honestly—These materials are intact—when thousands of years should have turned them to dust.” He leaned back slightly, thoughtful. “If I had to guess… This room was one of the primary experimental hubs of whoever built this dungeon.”

  He lifted his gaze, calm as a surgeon.

  "A high-level Inscribed Magic Circle seals it—the kind that preserves matter and environment, halting decay entirely."

  Sophia turned her head and surveyed the room again, properly this time.

  And she had to admit it.

  There weren’t even hairline cracks in the walls. No thick dust. No rot.

  Even the air carried a faint, clean scent—paper, old books, and something herbal underneath, oddly refreshing.

  If this place truly had been abandoned for a thousand years…

  it should’ve collapsed into ruin long ago.

  “Right.” Rein added, his eyes drifting to the towering shelves. “Time inside this room might be distorted even more than outside. Or…”

  He paused, then spoke the word carefully, as if setting it onto the table.

  “…it could be a Pocket Dimension.”

  He let the words settle.

  “With its own laws of physics and mana.”

  He tore his gaze away from the shelves and returned to the table.

  With care, he unrolled a scroll whose edges had begun to fray, flattening it open.

  “There are two things in here that are… extremely interesting.”

  Sophia leaned in to see.

  So close that her orange hair nearly brushed his shoulder.

  Her brows drew together the moment she saw the diagram.

  It wasn’t a natural cave map. No messy tunnels, no chaotic twists like the dungeons she knew.

  It was a ten-layer schematic—perfect geometry.

  Circles and squares stacked and interlocked with unnatural precision, orderly enough to look like abstract art.

  “This is…” Sophia breathed, genuinely stunned.

  “It looks more like magical topology than a dungeon map.”

  “Hm.” Rein nodded. “I noticed that too.”

  He traced a line across the diagram.

  “From what I can tell, we’re not inside a naturally formed dungeon. This is a gigantic Inscribed Magic Circle—a circuit carved into reality—engineered in the shape of a dungeon.”

  “And each layer was designed to perform a specific function.”

  His finger moved to the scattered black marks clustered at corners of the squares.

  “And these nodes—these energy convergence points…”

  He tapped one.

  “…are the nests of those monsters.”

  Sophia’s mind flashed back to the mountain of bones—the nest of the eyeless mantis-beasts she’d barely escaped.

  So that was why the density there had been so wrong. So unnatural.

  “I’ve never seen anything like this,” she murmured, a heaviness settling in her chest. “This isn’t a prison dungeon.”

  “It’s a machine.”

  Rein nodded once, quietly.

  “I have a hypothesis.” His voice stayed composed, but the implication was sharp. “This dungeon’s purpose isn’t imprisonment. They built it as a research facility—and a breeding ground—for bio-weapons in wartime.”

  He paused when Sophia’s expression turned blank.

  “Uh. People today just call them monsters. Their original purpose was mass production of killing units.”

  “War…” Sophia whispered. Then her eyes widened. “You mean—the Divine War from the legends?”

  “Yes.” Rein confirmed without hesitation. “If I’m guessing right, it’s that era.”

  He pointed to the major nodes.

  “The ten-layer structure connects through primary nodes that function as descent gates to the next layer. And of course…”

  His finger stopped, firm.

  “…each gate will have a Gatekeeper stationed there.”

  “You mean the ‘boss’ guarding the door.” Sophia said with confidence.

  She wasn’t some sheltered noble girl.

  She was a survivor—someone who’d lived through the Lancaster family’s brutal succession rite.

  A rite that threw bastard children into dungeons and waited to see who crawled back out.

  The bitterness rose—

  then snapped off as Rein’s knuckle rapped the notebook beside the map.

  He opened an old journal with a worn leather cover.

  “Normally,” Rein said, “dungeon bosses fuse a Monster Core into their bodies, right?”

  “Yeah.” Sophia answered bluntly. “And it’s what every mage wants. The higher the grade, the more expensive it gets—and the harder it is to find.”

  That was the veritable wall: money.

  The barrier every mage hit when trying to climb higher.

  Rein turned to her and smiled.

  “I’ve heard enough to know Monster Cores are the true bottleneck. That’s why major families—and even nations—fight over dungeon exploration rights. For what’s buried inside.”

  He raised a brow.

  “Am I wrong?”

  “That’s… true.” Sophia said slowly, leaning forward. “Wait. What are you implying—”

  “Yes.” Rein said, as if confirming an equation.

  “But here’s what’s different about this dungeon.”

  He pointed at the primary nodes again.

  “Kill the boss on each layer—and it won’t stay dead.”

  “Not for long.”

  “In this place… the boss-class monster will respawn, over and over.”

  Sophia jolted.

  “Respawn?!”

  This story has been taken without authorization. Report any sightings.

  Her voice trembled with alarm.

  “Rein—this is an S-Rank dungeon! If it keeps producing monsters nonstop, We need to alert the Disciples and seal this place before it overruns the kingdom!”

  She was already mentally drafting a plan to save the world—

  when her eyes flicked to Rein’s face.

  He didn’t look worried.

  Not even a little.

  Instead, his gaze held something else.

  A clean, surgical kind of greed—so pure it felt almost holy.

  Rein dragged his finger down the diagram, deeper and deeper, until it reached the tenth layer.

  Then he looked up and flashed her a wide grin.

  “Look at this, Sophia.”

  “Monster Cores. Everywhere.”

  He spoke like a man pointing at a gold mine.

  “This isn’t a hell-prison.”

  “It’s a resource factory. One that never goes bankrupt.”

  Sophia stared at him, speechless.

  Was this guy even sane?

  When everyone else would see catastrophe—

  Rein saw profit margins and a mountain of treasure, and he wore that expression like it was the most obvious thing in the world.

  “Based on what I’ve decoded,” Rein continued calmly, not even lifting his eyes from the papers, “the boss on the first layer is B-grade or higher.”

  “And naturally, the deeper we go…”

  His voice stayed flat, almost casual.

  “the cores become rarer, more valuable—and exponentially more dangerous.”

  “Rein.” Sophia cut in, shaking her head. “You’re forgetting something.”

  “Having high-grade Monster Cores doesn’t mean you can just walk up and refine mana.”

  She crossed her arms and exhaled sharply.

  “A Mana Refinement Ring is delicate and complex. Across the entire continent, only a handful can operate high-tier Refinement Rings correctly—and most of them are contracted to noble families, or bought out by superpowers.”

  Her eyes hardened.

  “And do you know how many top-grade cores you have to burn just to raise the success rate by a few percent?”

  “Even nobles with massive family backing fail—again and again.”

  The words carried the echo of her own scar.

  Sophia remembered the time the Lancaster family had “invested” in her—hundreds of C-grade cores—

  and it still couldn’t raise her breakthrough odds beyond twenty percent.

  The higher a mage’s mana density rose, the harder it became to condense a new circuit—because Inner Mana Resistance multiplies the strain geometrically.

  Rein listened without interrupting.

  He and LIZ had already analyzed Sophia’s data long before this.

  Even though she was only at Troposphere Master-tier, in the AGMT duel she’d taken down two opponents in Primary Stratosphere-tier on raw talent alone.

  That meant the mana inside her was too “thick” for her official tier.

  Trying to form new Core Mana Circles through standard refinement methods was, for her, practically impossible.

  “I know.” Sophia lowered her voice. Bitterness sat plainly in her eyes. “My power surpassed Troposphere-tier a long time ago.”

  “But I still can’t increase my Core Mana Circles. Refinement won’t go through.” Her jaw tightened. “And if I keep forcing it—if I fail a few more times…”

  Her gaze sharpened, almost hostile.

  “…my existing Core Mana Circles could collapse for good.”

  She stared him down.

  “That’s why most mages don’t gamble unless they’re absolutely sure. They won’t risk it.”

  A black pen suddenly appeared in Rein’s right hand.

  He rolled it between his fingers with easy, almost lazy dexterity—like a magician thinking through an act.

  Then he stopped.

  He tilted his head at the orange-haired girl who still looked caught between anger and resignation, and he delivered an answer that would shake every mage’s common sense.

  “It’s possible.”

  His voice was calm—too calm.

  “After spending the entire night decoding the texts in this room, I can build a new Mana Refinement Ring.”

  He lifted a finger, counting with the certainty of a formula.

  “Give me six B-grade monster cores.”

  “And I’ll show you what a one-hundred percent refinement success rate actually looks like.”

  For a second, Sophia felt like she’d heard something so detached from reality it could only be the arrogance of someone who didn’t understand the world.

  She couldn’t help snapping back, serious this time.

  “Rein.” She stepped closer, eyes hard. “Even burning six B-grade cores only pushes the odds to fifty percent at best. The rest is luck—pure luck!”

  “And you don’t “invent” a refinement ring just because you read a few ancient texts.”

  Her voice sharpened as she pressed him.

  “As far as I know, some geniuses can use special artifacts to push the percentage a little higher, but—no one in Aetheria’s history has ever pushed refinement past sixty percent. Not once. Not ever.”

  But before she could finish—

  the black stone floor of the hall trembled faintly.

  Then it lit up.

  A deep cobalt glow bled outward—like ink dispersing through still water.

  Tens of thousands of ancient runes erupted from the ground and aligned themselves—layer upon layer—into a colossal, Mana Refinement Ring—spanning more than twenty feet across.

  Sophia’s voice cracked.

  “T-That’s… a Mana Refinement Ring!”

  Her breath caught.

  The mana within it felt pure. Stable. Clean in a way she had never experienced before in her life.

  “Are you insane…?” she whispered, stunned. “How—how can you do this?”

  She whipped around to Rein, caught between awe—and something colder. Fear of something that no longer felt human.

  Rein didn’t answer how.

  He only curved a faint smile at the corner of his mouth, blue eyes glittering with reflected rune-light.

  “All right,” he said softly.

  “So… do we have a deal?”

  …

  Three hours later—

  After weaving through winding routes to avoid the hungry swarms of eyeless mantis-beasts, the two finally reached their target.

  But neither of them looked good.

  To mask both “human scent” and their foreign mana signature, they had to smear themselves head to toe with the reeking fluid from the dead mantises.

  Naturally, Sophia didn’t stop complaining for even a second.

  Rein smiled under his mask.

  He understood her perfectly.

  No girl—especially one who had just soaked in a heavenly hot spring—wanted to coat her freshly clean skin in something that smelled like vomit given physical form.

  Peering down from an old brick ventilation shaft only four feet wide, they saw it.

  A massive hall—the main nest.

  And at its center stood the Mantis King.

  Nearly three stories tall.

  It loomed atop a mountain of bones more than six meters high, its black scythe-like blades catching faint light in a sick sheen.

  Thick armor plated its entire body, radiating pressure like a storm given flesh.

  B Grade.

  Possibly higher.

  Behind the mantis monarch stood a gigantic metal gate—the descent to the next layer.

  But reaching it wouldn’t be simple.

  Hundreds of eyeless mantis guards wandered and swarmed around it like an ant army with blades for hands.

  Sophia’s brows knitted together as she whispered, grim.

  “That thing isn’t normal… In standard terms, Taking it down would require at least two or three high-rank parties.”

  “Someone has to hold off those hundreds of minions while the main team piles onto the boss—otherwise we get torn apart before we even scratch it.”

  But the boy beside her offered a plan so reckless it bordered on madness.

  “Simple plan, Sophia.” Rein said.

  “You go down and draw the minions away from the nest. Pull them far. As far as you can.”

  “And that big one…”

  His voice didn’t rise. It didn’t shake.

  “I’ll take care of it.”

  “Wait—are you out of your mind?!” Sophia almost yelled—then forced her volume down at the last second, teeth clenched. “Solo a B+ boss with armor like that? What are you thinking?!”

  Instead of arguing, Rein repeated the order—sharp enough that Sophia could only stare into his eyes in the darkness.

  Then she exhaled in frustration.

  “Fine. With my speed, luring them won’t take long.”

  She narrowed her eyes.

  “Just don’t die before I get back.”

  “I’ll come back and help.”

  The moment Sophia dropped from the vent, she opened with violence—

  she cleaved the nearest guard mantis clean in half.

  Green blood sprayed across the floor, loud and vivid, drawing the entire nest’s attention at once.

  Wind magic wrapped around her body.

  She vanished in a blur, accelerating and lured hundreds of minions to chase her until the nest was nearly empty.

  But anxiety churned in her chest.

  Rein alone can’t do more than stall a B+ boss…

  If she didn’t return fast enough, he’d become another bone pile in this nest.

  She wanted the breakthrough with everything she had—

  but she wasn’t selfish enough to trade someone’s life for it.

  After scattering the swarm across multiple corridors, Sophia snapped back toward the nest at maximum speed—

  only to halt so abruptly she almost lost her footing.

  Rein was… sitting casually atop the massive corpse of the eyeless mantis king.

  The head had been removed with surgical precision.

  The cut was so smooth it looked like a blade both impossibly hard—and impossibly sharp had made it.

  Sharp enough to shear through obsidian-steel armor like paper.

  “Here.” Rein tossed something to her without even looking up.

  “First Monster Core.”

  Sophia caught it on reflex, dazed.

  A B+ core—extracted with meticulous precision.

  A clear green gem—like flawless emerald glass—roughly the size of a human heart—trembling with densely packed mana.

  “Y-You…” Sophia’s voice wavered with disbelief. “You’re not going to keep it for yourself?”

  For a first-year student, a B+ core was the kind of resource that could change a life.

  “I don’t need it.” Rein said flatly.

  His eyes shifted to the gate leading downward—the way to the next layer, now standing open.

  Sophia’s lips curled into a mischievous smile, as if to patch over her own confusion.

  “Or what… are you actually just into me?”

  She twirled a strand of her orange hair, teasing in the dim light.

  “But I’m warning you—just because you hand me six cores doesn’t mean I’m agreeing to be your girlfriend that easily.”

  Rein made a face like he’d just bitten something sour.

  He shook his head and cut away from the nonsense immediately, yanking the atmosphere back into seriousness.

  “According to that journal—and my calculations…” Rein said, standing and dusting off his pants, “This boss takes roughly two hours to respawn.”

  “So here’s my proposal.”

  “Instead of sitting here for two hours inhaling corpse stench, we go down and scout the deeper layer.”

  “I expect the next one will have A-grade monsters. Their cores will stabilize your refinement far better than anything you’re holding right now.”

  Sophia stiffened. The playful smile vanished instantly.

  “Hold on,” she said, voice tight.

  “Are you telling me… we’re about to run an S-Rank dungeon with just the two of us?”

  “You’re serious?”

  It felt like she was stepping into a pit so deep she might never climb back out.

  “Yes.” Rein replied lightly—like he was inviting her for a walk in a backyard garden.

  “But not clearing all ten layers in one go.”

  “We’ll take two or three layers—just enough to secure what we need.”

  “Then we retreat to the hub, rest, and start the refinement process there.”

  He looked at her.

  “Deal?”

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

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

  Monsters

  Eyeless Mantis King

  The B+ rank boss monster guarding the first descent gate. A massive, eyeless mantis creature that radiates deadly pressure. Rein defeats it solo with surgical precision and extracts its core for Sophia’s use in refinement.

  Magic and Spell Techniques

  Inscribed Magic Circle

  A high-level magical structure etched into physical reality, capable of producing complex magical effects on a massive scale. In this chapter, the entire dungeon is revealed to be one such structure: a ten-layer circuit engineered in the shape of a dungeon, designed not for imprisonment but for bio-weapon research.

  Mana Refinement Ring

  A complex magical structure used to refine Monster Cores and condense them into new Core Mana Circles. Only a few skilled specialists can use them successfully. Rein, after studying ancient texts, constructs a fully operational Mana Refinement Ring within the Pocket Dimension, offering 100% refinement success rate—something never before achieved in history.

  Magical Topology

  A term used by Sophia to describe the dungeon’s schematic. Unlike naturally formed dungeons, this structure features perfect geometry—circles and squares arranged in symmetrical layers, hinting at artificial, arcane engineering. Resembles a fusion of magical and mathematical design.

  Resource

  Monster Core

  A dense crystal of mana condensed inside high-tier monsters, often embedded within dungeon bosses. These cores are rare, highly valuable resources used for mana refinement. Rein identifies the dungeon as a renewable source of Monster Cores due to the bosses’ ability to respawn—a discovery he likens to a “resource factory.”

  Concept

  Pocket Dimension

  A sealed, self-contained space that exists with its own independent laws of physics and mana. The room Rein and Sophia discover in the dungeon shows signs of such a dimension—it is preserved in perfect condition despite being thousands of years old. Rein suggests a high-tier Inscribed Magic Circle is responsible for halting decay and time inside the room.

  Gatekeeper / Boss Monster

  A powerful monster stationed at the descent gate between dungeon layers. In this artificial dungeon, bosses respawn after being defeated, making them renewable sources of Monster Cores. Rein plans to exploit this feature for high-grade core farming.

  Inner Mana Resistance

  A natural barrier that increases with mana density. As a mage advances in power, it becomes harder to condense new Core Mana Circles due to internal resistance. This is the primary reason breakthrough rates drop sharply in high-tier mages.

  Core Mana Circle (Update)

  The internal magical structure within a mage that stores and channels mana. The number and quality of Core Mana Circles determine a mage’s tier and capabilities. Advancing requires successful mana refinement using Monster Cores—failure may damage or collapse existing Circles.

  Monster Respawn Mechanism

  Unique to this dungeon, boss-class monsters regenerate after being killed. Rein theorizes this is due to the dungeon’s design as a research and weaponization facility. This feature transforms the dungeon into an infinite supply of cores, ideal for mana refinement and power scaling.

  Refinement Success Rate

  A statistic measuring the odds of successfully integrating a Monster Core into a Core Mana Circle. Traditionally very low, even with expert assistance and high-tier cores. Rein claims he can achieve a 100% success rate using a newly constructed refinement ring based on decoded ancient methods.

  Dungeon Ranks

  S-Rank Dungeon

  The classification given to the dungeon Rein and Sophia explore. S-Rank dungeons are the most dangerous type, typically requiring elite teams to clear. Rein proposes to run multiple layers with just the two of them, thanks to the dungeon’s structured design and renewable resources.