My Special Ability is Growing Muscles

The night bled fire.

Deep in the Human Domain, the forge district of Ironvale blazed like a dying star. Towers of molten chimneys toppled, furnaces ruptured, and the screams of smiths and apprentices were drowned beneath the grinding of bone.

At the heart of it all stood a colossal figure… Kravox Bone-Tyrant, one of the 8 Demon Lords of the Demon Council.

Eight feet tall, plated in a blackened bone armor fused from thousands of corpses, he was like a God of Death itself.

His helm that was designed like a Demon skull grinned with eternal malice, fangs jutting down like scythes. In his clawed hands, a crooked staff dripped marrow as it pulsed with necrotic flame.

Around him, his legion stirred.

An army of skeletal horrors, smiths, guards, and civilians all corrupted by his powerful demonic energy raised again within minutes of their deaths, bones clicking as they fell under his dominion.

This was why he was a terror of the Demon Race.

Against the Bone Tyrant, you were not just fighting against a single S Ranked Demon, due to his profane abilities, you were literally fighting against an army, an army of bones.

Kravos Bone-Tyrant was perhaps the only one of the 8 Demon Lords of the Demon Council who could claim the title of one man army.

Every clang of the hammer and every groan of breaking stone in the forge was answered by another corpse pulling itself from the rubble to serve him.

"Stop him!" The forge masters shrieked in desperation and panic.

"Where are the guards?! What are they doing?"

"Ahhh… stay away from me… ARGHHHH!"

"Heretic Demon, you'll pay for this!"

The forge masters and their apprentices resisted, they tried, but it was all for naught in the face of this powerful Demon Lord.

"Break their chains," Kravox hissed, voice a rasp of grinding teeth and in response, Bone Serpents slithered through alleys, constricting panicked humans.

War constructs made of ribcages and furnace metal rose from the wreckage, swinging molten hammers back at their creators.

The great forges of Ironvale, humanity's lifeblood of weapons and armor, collapsed one by one, unraveled by a single Demon Lord. All of their defenses were broken down by him methodically, one after the other.

They were helpless, they stood no chance unless reinforcements came.

But that was the thing. The Demons planned their attack to perfection. They attacked when the human domain was least protected, when the strongest Heroes of the human domain were out on expeditions to other dimensions.

It was a perfect plan, and Kravos Bone-Tyrant executed it to perfection.

Spellsteel veins cracked, reservoirs of enchanted ore flooding with necrotic fire as he rampaged through the forges.

His laugh echoed through the choking smog. "Haahaahahaha!"

"MUAHAHAHAHA!"

"Let them march to war without their steel, let them drown in ash and marrow!"

"We shall spread them bare and vulnerable".

Every strike of his staff shattered another anvil. Every gesture raised another thrall, and the entire forge district became one graveyard armory, a kingdom of bones under his heel.

But then, after minutes of going at it, wreaking untold havoc and devastation in the forges, the ground suddenly trembled.

BOOM!

Through the smoke descended a beacon of golden fire. Reinforcement.

A knight clad in gleaming armor appeared, crest of the Hero Union blazing on his breastplate. His sword was pure radiance, a sun forged into steel.

Sir Ardent Solarion, an S-Rank Hero of humanity, sworn defender of the Northern provinces.

"Kravox!" He roared, his voice shaking the city's ruins, his rage manifesting as a tyrannical golden aura that engulfed his body and his surroundings. "You dare come all the way here alone?!"

"You truly court death!" He snarled. "You will fall here!"

"Pay for your crimes!"

He charged, blade blazing, carving through waves of skeletons like wheat. Each swing was an inferno, each step a vow of protection.

He didn't move like a man at all, rather, he moved like a force of nature.

Every movement of his seemed to shake the world.

KABOOM!

But Kravox only cackled. His staff cracked against the earth, and the ground split open. Colossal bone giants rose, stitched together from the corpses of smiths and guards, wielding furnace doors as shields, chimneys as spears.

"Fall? Ha! I have already won". He laughed without care.

And then, they clashed.

Solarion's sword blazed with holy wrath, cleaving a bone giant in half. His aura burned through bone serpents, turning undead to ash with every pulse.

But for every abomination he destroyed, Kravox raised two more. The entire city pulsed with necrotic veins, the bones of thousands answering the Tyrant's call.

Solarion's fury lit the night, his sword splitting sky from earth but his face hardened as he realized the truth. The forges were gone, the supplies were gone. Humanity's weapons, its war machines, its lifeblood of steel… all destroyed.

The damage was done and there was nothing he could do about it.

And though he knew that he could not kill the Bone Tyrant immediately in a head-on clash, fueled by rage, he attacked furiously anyway.

Kravox's laughter was a rolling thunder. "You burn bright, little Hero… but tell me, what good is light when there is nothing left to protect?"

With a final wave of his staff, Kravox collapsed the last of Ironvale's foundries. Towers of enchanted steel fell in a cascade of fire and dust.

Solarion roared, lunging at him, sword blazing like dawn. But Kravox simply vanished into a storm of bones, his voice echoing through the ruins.

"Hahahaha! You are too late! The forge of men is broken, now let them fight their war with sticks and prayers!"

When the dust cleared, the knight stood alone amidst the wreckage, sword trembling. Around him, nothing remained but ruins and an army of lifeless bones crumbling to dust.

High above the smoking city, Kravox reformed in the night sky, his skeletal wings unfurling. He looked back once, savoring the ruin.

"The Demon King will be pleased," he rasped, grin widening. "This world will kneel on bones."

And with that, the Bone Tyrant vanished into the shadows of the continent.