Endless Evolution as an Undead

SSS Rank Dungeon — Demonic Fortress

“Avoid it!” Arthur shouted, his throat burning from the demonic mana present in the room, along with the suffocating smell of burning wood in the background.

In front of him was the Demon Lord, a massive entity hated by all races. The one who radiated intense demonic mana unlike any demon they had faced before. The entire space seemed to bend to his will. Even the pressure released by him was enough to make normal people collapse in an instant.

Behind Arthur, his squad was already falling apart.

“Don't just stand there! Move!” Arthur shouted, fighting through the deafening ringing in his ears.

With every ounce of strength left in his battered legs, he lunged forward, thrusting his longsword to intercept the Demon Lord's heavy blow—a monstrous cleaver made from raw black metal.

Clang!

The massive impact crashed through his arms, nearly shattering his bones.

“Tank! Shield wall! The right flank is wide open!” Arthur ordered.

Moving out from his previous position, he drove his blade deep into the Demon Lord's shoulder joint, finally delivering a massive cut.

For a split second, Arthur looked back at his team, who were already falling apart, barely able to keep themselves upright.

Edward, the hulking tank of the party, was trembling violently, his knees knocking together under the weight of the Demon Lord's gaze. Clara, the priestess, fumbled with her magic circle; her hands shook so badly that her incantation kept flickering out. The mage could only manage to cast sluggish, delayed fireballs, and the archer’s arrows barely stuck into the beast’s hardened hide before falling away.

They were entirely paralyzed by the sheer terror of death. If left alone by themselves, they wouldn't even last ten breaths before being slaughtered by the Demon Lord in seconds.

“It falls to me again,” Arthur whispered silently under his breath.

There was no time for anger. Gritting his teeth, he channeled his remaining stamina into a furious, relentless onslaught.

For a legendary hero like him, he was already in tune with the attack patterns of the Demon Lord, barely dodging every sword strike and magic attack while striking the Demon Lord whenever he got the chance.

Carrying the entire chaotic battle on his shoulders, he was dealing ninety percent of the damage alone, almost as though he was carrying his team, but he couldn't complain. It wasn't like this was the first time. A party formed from nobles and the Church only wanted fame and fortune, basking in the glory of the hero's party.

“Mage, suppress the left side! Archer, target the eyes on my mark!”

With one final, desperate surge of strength, Arthur jumped off a crumbled stone pillar and drove his longsword straight through the Demon Lord’s glowing red heart.

The Demon Lord froze.

The oppressive aura around it flickered slowly before finally dissipating as the creature let out one final rattling breath before dissolving into a mountain of ashes.

Silence fell over the throne room.

Arthur collapsed to his knees, coughing violently. He drove his longsword deep into the stone floor to support himself from falling face-first onto the ground.

It was over.

They had successfully cleared the SSS-rank dungeon.

Footsteps slowly approached.

“Arthur...”

It was the assassin of their party, Clara. Her voice was soft and honey-like amidst her frequent gasps for air. Without waiting for Arthur to turn his head and look at her, she rushed forward, wrapped her arms around Arthur’s neck, and hugged him tightly.

The tension drained out of Arthur, replaced by a wash of profound relief. Even someone as cold and calculating as Clara had broken down in celebration.

“We... we won,” she whispered against his ear.

“Yeah,” Arthur murmured back, a tired, genuine smile touching his lips. “We finally did it.”

Shhhk.

Arthur’s smile disappeared, and he felt a searing burning sensation across his lower back.

Looking down, Arthur saw a dagger protruding from his abdomen, dripping slowly with his blood.

“Wh—what...?” Arthur choked out, his hand trembling as he reached back.

He tried to turn his head, but his limbs became heavy, refusing to obey.

The assassin ripped the blade out with a clinical motion, then stepped away from Arthur.

Arthur collapsed onto his knees, coughing out a mouthful of blood.

Behind him, the rest of the party appeared from the shadows. The fear that had paralyzed them in battle was completely gone, replaced by cold indifference.

“Why... Why is my body numb?” Arthur gasped, staring up at them with hatred in his eyes.

Clara smirked, spinning the blood-stained dagger between her fingers.

“Special order, Arthur. A custom paralyzing agent, formulated specifically for our great hero. Months of planning, together with the capital's top alchemists.”

“Consider yourself honored,” the Mage said, adjusting his robes with a cold, mocking chuckle. “Do you have any idea how much funding it took us to get a poison prepared especially for you? You should be honored to be so important.”

“We’re going to report to the capital that you died bravely slaying the Demon Lord,” the Priestess added, crossing her arms without a hint of remorse. “Your sacrifice will be remembered forever. Really. The Church and the Empire will make sure your name goes down in history.”

Desperate, Arthur tried to force his mana to surge, to fight back. Instead, a sharp, icy frost flooded his veins.

The poison paralyzed him and actively blocked his mana, choking off his legendary constitution as easily as it would a common man's.

Arthur’s vision blurred at the edges. The faces of his comrades twisted and distorted into a spinning vortex of darkness.

Thud.

Arthur’s chest hit the cold stone floor. His tongue went numb. The pounding in his ears slowed, then stopped.

The hero was dead.

---

Three Days Later

The party had long since departed the dungeon, leaving Arthur’s body behind to rot in the dark.

The throne room was silent except for the huge pile of ashes from the fallen Demon Lord.

Slowly and almost unnoticed, the remaining aura of death from the Demon Lord’s ashes started to awaken.

It curled into thick, slow smoke and started to creep along the floor. Drawn by an invisible magnet, the black smoke converged on Arthur’s lifeless body, swirling around his chest before sinking deep into his pale, cold skin.

Deep within the quiet stillness of death, a single spark ignited.

«[System Alert]

Condition met: User has died.

Mythical Rank Skill [DEATH] activation sequence initiated.

User status check: Heartbeat stopped. Vital organs necrotized. Body temperature: subzero.

Executing recovery protocol: Harnessing the energy of the Abyss to restore life functions...

Loading... Loading... [FAILED]

Loading... Loading... [FAILED]

Loading... Loading... [FAILED]

Loading... Loading... [FAILED]

Loading... Loading... [SUCCESS]

Congratulations to the user for activating the Mythical Rank Skill [DEATH].»

In the dark, blood-stained stone of the SSS-rank dungeon, deep underground, a pair of empty eye sockets opened in the pitch-black darkness.