My Perfect Isekai: Pragmatic Protagonist, Progression Fantasy and Strategy

The fifty-ninth floor of the Crossgard dungeon did not offer the crystalline geometry of the levels above, nor the oppressive, two-hundred-degree furnace of the slag abysses. It was a subterranean drowned canyon—a vast, pitch-black chasm carved through millions of tons of ancient basalt, flooded by an underground river of boiling, mineral-dense brine.

Sulfuric steam curled from the dark water, clinging to the jagged rock walls in heavy, suffocating curtains. The ambient temperature lingered at a humid, skin-blistering ninety degrees Celsius, but inside our five-meter sphere of Sapphire Slime, the air remained at a crisp, perfectly regulated eighteen degrees.

”Tactical radar clear, boss!” Kaede’s cheerful, high-pitched ping echoed in my left ear in our native Polish operational cipher. ”Płyniemy korytem podziemnego kanionu! Czujniki wyłapują potężne wstrząsy pod powierzchnią tej gorącej solanki! Coś wielkiego idzie pod prąd z pięćdziesiątej dziewiątej piętrówki! Szefie, ten kloc pcha przed sobą tysiąc ton wrzącej wody!”

”Let it push,” I replied smoothly, my hands loosely tucked into the pockets of my dark coat. ”Water is just a fluid medium. It obeys mass, velocity, and pressure. Nothing more.”

Beside me, Shnee stood with her Celestial Silver rapier held in a relaxed, low guard. Her ice-blue eyes scanned the bubbling, dark surface of the brine river with cold, predatory focus.

”The current is accelerating, Dave,” she noted softly, her voice cool and steady despite the stifling steam outside our thermal barrier. ”The aquatic creatures in this biome rely on hydraulic pressure to crush their prey before dragging them into the trench.”

”They can rely on whatever physics they want,” I said calmly. ”Until they hit a wall.”

A fraction of a second later, the dark river erupted.

A colossal wave—a forty-meter subterranean tsunami of boiling, mineral-thick brine—surged out of the cavern’s gloom, filling the entire width of the canyon. Pushed by an immense, unseen force, the wall of water roared toward our narrow basalt ledge at eighty kilometers per hour, threatening to sweep our entire party off the rock and drown us in the scalding abyss.

Hidden within the crest of the boiling wave was the architect of the surge: a thirty-meter-long Slag-Crested Leviathan. Its armor consisted of interlocking plates of petrified basalt and volcanic glass, fused together by centuries of geothermal pressure. Crimson, glowing runes pulsed along its spine, driving its hydraulic tail with terrifying power.

”Szefie! Tsunami na sterydach!” Kaede yelped, her small spider legs tightening around my collar. ”Brak miejsca na uchylenie się na półce skalnej! Boczny unik odpada, spadniemy w przepaść!”

”Who said anything about dodging?” I muttered.

I took one step forward, stepping directly onto the edge of the wet basalt ledge. I unbuckled a mental valve in my energy pathways, letting the dense, gold-blue currents of my newly awakened Pyrite Core surge through my broadened mana weaves. The upgraded Pyrite Core in my modernized Vessel hummed with an absolute, frictionless density, operating at a effortless eighteen percent capacity.

Instead of erecting a static shield, I extended my right arm forward, extending three dozen thick, sapphire-blue tendrils of slime from my coat sleeve.

”Kinetic Ramp, invert thirty-five degrees,” I commanded inwardly.

The tendrils expanded into a broad, parabolic wedge of dense, frictionless Sapphire Slime, angled precisely to intercept the forty-meter wave. When the multi-ton wall of boiling brine slammed into the barrier, it didn’t smash through our position. Guided by the zero-friction surface and the parabolic curvature, the entire tsunami was redirected upward and over our heads, arching harmlessly across the canyon vault in a massive, roaring geyser that splashed into the abyss behind us.

Inside our thermal sphere, not a single drop of boiling water touched us.

The Slag-Crested Leviathan, carried mid-surge by its own immense forward momentum, suddenly found itself stripped of its water cushion. It launched out of the redirected wave, flying straight toward our ledge with its jaw unhinged—a maw lined with three rows of razor-sharp, volcanic obsidian teeth.

”Shnee, disable its lateral balance,” I ordered quietly.

”Understood,” the white-haired elf replied instantly.

She blurred forward like a streak of silver light. Leaving the safety of the sphere for a fraction of a second, her Celestial Silver rapier executed a lightning-fast double thrust. She didn’t attempt to pierce the leviathan’s two-meter-thick head armor; instead, she drove two concentrated needles of extreme frost mana straight into the monster’s left gill slits.

The sudden, brutal drop in temperature froze the creature’s internal hydraulic pumps mid-cycle. The leviathan’s left side seized instantly, causing its thirty-meter body to tilt violently in mid-air, exposing the soft, unarmored cartilage beneath its throat.

”My turn,” I said calmly.

I stepped off the basalt ledge, launching myself straight toward the airborne monster. I didn’t bother drawing a weapon. As I closed the ten-meter gap in mid-air, I coated my entire right arm from fingertips to shoulder in the pitch-black, light-absorbing shell of my Gōtai. Powered by the refined density of my Pyrite Core, the black aura hummed with an absolute, light-warping stability.

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”Kinetic Compression: Diamond Spike,” I whispered.

I drove my right hand straight into the exposed cartilage beneath the leviathan’s throat. The black Gōtai armor, sharpened to a monomolekular point by my telekinetic compression, penetrated the thick hide like hot iron through lard.

Once my hand was buried three feet deep inside the monster’s chest cavity, directly adjacent to its pulsating purple core, I unbuckled the main output valve of my energy channels.

”Disposal,” I commanded cold-bloodedly.

I unleashed a triple-voltage discharge of pure Sapphire Lightning directly into the beast’s central nervous system and core matrix. The gold-blue electrical impulse blasted through its circulatory pathways in a fraction of a millisecond.

BOOM!

The internal pressure of the electrical explosion shattered the leviathan’s internal organs instantly. Steam and purple sparks erupted from its gill slits and eye sockets. The thirty-meter monster froze mid-air, its crimson runes flickering out before its entire volcanic chassis collapsed inward, breaking apart into harmless piles of gravel, cracked obsidian, and steaming ash.

I caught the purple core—a glowing sphere the size of a watermelon—in my left hand, landed lightly back on the basalt ledge, and slid my hands back into my coat pockets.

”Radary czyste, szefie!” Kaede cheered, her spider legs doing a little victory dance on my shoulder. ”Pięćdziesiąta dziewiąta piętrówka zamknięta w niecałe trzy minuty! Ten kloc nawet nie zdążył pomyśleć o przetrawieniu nas! Zero zużycia kalorii, a rdzeń jest wielkości arbuza!”

”Pack it up,” I said, tossing the purple core to Shnee, who caught it deftly and stowed it in our dimensional satchel. ”The sixtieth floor is right ahead. The final gate of the sixth decade.”

The archway leading to the sixtieth floor was forged from solid, ancient iron, encrusted with centuries of mineral salt and basalt corrosion. Beyond the heavy portal lay a colossal, circular amphitheater—the heart of the subterranean canyon.

The ground here was composed of polished, black obsidian, illuminated by rivers of liquid fire that flowed through deep trenches in the floor. Sitting in the center of the arena, resting its massive chin on a twenty-ton basalt war hammer, was the ruler of the sixth decade:

The Subterranean Iron Colossus.

It stood eighteen meters tall—a towering titan of ancient, runic iron and hardened slag. Its chest plate was three meters thick, glowing with a deep, crimson light where its master core burned. Unlike the mindless beasts of the upper levels, the Colossus possessed an ancient, tactical instinct. The moment our boots stepped onto the obsidian floor, its crimson eye-slits flared to life with a low, mechanical hum.

”Szefie! Ten kloc ma pancerz z pięciokrotnie przetapianego żelaza runicznego!” Kaede reported sharply, her operational pings coming fast and precise. ”Jego rdzeń jest osłonięty podwójną klatką grawitacyjną! Każda próba ataku frontalnego zostanie odbita przez jego pole magnetyczne!”

”A magnetic field requires a closed circuit,” I observed dryly, taking a slow step forward. ”Break the circuit, and the field collapses.”

”Shall I attack the joints, Dave?” Shnee asked, her rapier gleaming with cold frost mana.

”No,” I replied, raising a hand. ”I want this done cleanly. We have an appointment back in Oakhaven with a full table of Mina’s roast pork, and I don’t intend to spend the evening scrubbing slag off my coat.”

The Colossus rose to its full eighteen-meter height. With a deafening metallic screech, it lifted its twenty-ton basalt hammer with both hands, bringing it down toward our position in a devastating, parabolic overhead smash. The sheer air displacement alone created a sonic boom that cracked the obsidian floor before the hammer even landed.

”Stand behind me,” I instructed quietly.

Shnee and Kaede didn’t hesitate, stepping smoothly into my shadow.

I didn’t move an inch. As the twenty-ton hammer descended at two hundred kilometers per hour, I raised my right hand, extending a single, ultra-dense tendril of Sapphire Slime straight up to meet the falling weapon.

”Friction coefficient: absolute zero,” I muttered.

The moment the massive basalt hammer struck the sapphire tendril, the zero-friction surface completely negated the transfer of kinetic energy. Instead of crushing us, the twenty-ton weapon slid off the parabolic slime curve at an angle, smashing harmlessly into the obsidian floor two meters to my right with a earth-shattering THUD! that shook the entire amphitheater.

The Colossus, thrown completely off balance by the sudden loss of resistance, stumbled forward, its massive chest plate tilting downward toward the floor.

”Circuit broken,” I said coldly.

Before the titan could recover its posture, I launched myself forward in a straight line of force. I closed the fifteen-meter gap in a fraction of a millisecond, appearing directly in front of the Colossus’s three-meter-thick chest plate.

I coated both my hands in the pitch-black, light-warping armor of my Gōtai, infused with the golden-sapphire charge of my Pyrite Core.

”Double Impactor,” I whispered.

I slammed both palms simultaneously into the seams of the titan’s iron chest plate. I didn’t try to punch through three meters of solid iron; instead, I injected two opposing, high-frequency kinetic pulses directly into the armor’s structural stress points, matched precisely to the natural resonance of runic iron.

CRACK-THOOM!

The harmonic shockwave vibrated through the eighteen-meter frame. The two-meter iron plates didn’t just dent—they depolymerized on a molecular level, shattering into millions of tiny, glowing iron filings that rained down onto the obsidian floor.

The Colossus’s master core—a blinding, pulsating purple sphere the size of a wine barrel—was now completely exposed.

I reached out with my right hand, wrapping my black Gōtai-coated fingers around the hot core. With a cold, effortless twist of my wrist, I severed the mana conduits connecting the core to the chassis.

”Liquidated,” I said softly.

The eighteen-meter titan froze instantly. The crimson glow in its eye-slits died. A second later, the entire iron chassis collapsed into an inert, lifeless heap of scrap metal and steaming ash.

I held the colossal purple core in my hand, feeling the immense, warm energy radiating from its surface. The Pyrite Core in my chest hummed in quiet appreciation, absorbing a fraction of the ambient energy to top off my reserves.

”Radary czyste, szefie!” Kaede shouted, jumping up and down on my shoulder. ”Sześćdziesiąte piętro leży i kwiczy! Cała szósta dycha odhaczona! Mamy komplet fioletowych rdzeni, zero uszkodzeń w sprzęcie i idealny harmonogram na kolację u pani Eleny!”

”Good,” I said, turning on my heel as the azure portal to the surface opened at the back of the amphitheater. ”Let’s go home. The dungeon can wait until tomorrow.”

Shnee smiled gently, sheathing her rapier with a soft click. ”A very efficient raid, Dave.”

”Engineering always is,” I replied smoothly, sliding my hands into my pockets and stepping into the blue light.