My Special Ability is Growing Muscles

'God… I'm tired!'

Kairo punched.

He punched again, and again, and again.

All his muscles ached. His bone joints creaked like cords of a machine that were suffering from too much wear and tear, and needed a comprehensive overhaul. He was pushed to his wit's end.

Not even the combat phase of the entrance tournament into Nexus Academy pushed him this much.

At least, then, he fought against other boys of his age. Prodigies, yes, but still they were boys of his age.

But this time, he fought against Demons.

Of the 5 races in Planet Scrontum, the Orcs had the strongest and most enduring physique, but right behind them was the Demon race. The Demons had one of the most frightening and intimidating physiques.

And of the 5 races, humans were right at the very end alongside the Elven race when it came to physique.

The Elves' unnatural affinity to mana and nature more than made up for it though. As for humans, if they had one redeeming quality, it had to be their adaptability.

Adaptability… it seemed like an underwhelming trait but it was the core of the human race.

It was what kept them alive and protected them from going extinct in a world where their neighbors had so much innate talent and nature-given advantages.

And it was also what kept Kairo going.

It was also what kept the surviving applicants alive against the Demon onslaught, when it seemed like all hope was lost.

Having been fighting all the way from the night massacre to 6 brutal rounds of combat, every single survivor among the applicants were already at their wit's end, exhausted, tired, and their bodies longed to rest.

This was why at first when the commotion started, they were rattled so deeply because even psychologically, they were not in their optimal state.

And when the barrier protecting the combat arenas shattered, it was also why at first, they devolved into panic, unable to handle the situation.

At first, Kairo also devolved into panic, but then, one thought pushed him to survive. 'Leora…'

'Fight!' He had to fight, he must fight, he must survive!

With his body already shriveled up at that point, tired and exhausted both physically and mentally, Kairo had no business surviving a battle against Demons but adaptability kept him going.

Adaptability kept him standing, and it was what also enabled him to awaken his new ability skill when he needed it the most.

With Monarch's Roar, he adapted to the situation, rallying the survivors, boys and girls that were once his bitter rivals so they could fight together.

All they needed was calm.

Because in the end, though tired, they were equipped to survive.

In that group were some of the strongest 16 year olds of humanity. There were defensive experts, versatile fighters, and offensive juggernauts in the group. All they needed was calm to bring out the best of their abilities.

Desperation did the rest.

Pushed against the wall, their enduring will to survive against all odds pushed them to stand their ground against the Demon horde and annihilate the horde of F-Rank Demons that charged them first.

They survived, but fate was cruel. That was not enough as they faced a bigger test in the form of E-Rank Demons.

Humans were adaptable, but there is a limit to their adaptability.

Fighting a rank above their weight when tired and exhausted should have been the breaking point, but once again, Kairo struck with Monarch's Roar.

It was crazy, it was illogical, but with this new ability of his, Kairo actually managed to convince these boys and girls that they stood a chance against E-Rank Demons. On a normal day, he would have been ridiculed and laughed at.

But today was as far from normal as any day could, and so, these boys and girls rallied to defy heaven and defy fate.

They fought, they survived.

Some of them died, all of them suffered grievous injuries of varying degrees, but at the end, willpower pushed majority of them to the finish line.

The horns came first.

HOOOOONK!

Reinforcement was here, finally.

The ground quaked as human banners streamed through the shattered coliseum gates. Cavalry thundered across the blood-soaked floor, shields locked and lances raised as human warriors came for blood.

Mage battalions lined the flanks, incantations already glowing on their lips as the atmosphere became supercharged with mana.

Above them, beast riders swooped in on gryphons and wyverns, their shadows cutting across the broken arena as they hunted the Demons.

E and F-Rank Demons could not fly with their wings, but D-Rank and above could. These were the Demons that the beast riders hunted down, every one of them a juggernaut of humanity.

"Reinforcements!" Mira gasped, her voice trembling with disbelief.

The E-Rank Demons finally stopped their assault.

The surviving applicants staggered where they stood, bloodied and hollow-eyed. Some dropped to their knees in relief. Kairo leaned heavily on Mira, his body shrunken and shriveled again from the toll of Muscle Genesis, but his gaze burned.

"They came," he whispered, his gaze burning feverishly. His cracked lips curled into a weak grin, fists still trembling with stubborn defiance.

Above the carnage, three titanic figures finally paused their assault.

Malgar Voidborne's silver eyes flicked to the gates as fresh waves of human forces poured in. His void-laced blade dripped with the blood of instructors, but his smirk was calm, calculating.

"Not victory," he murmured, "but this is enough".

As he said, his eyes scanned the coliseum beneath him, looking at the extent of damage that they just did in just a few minutes to the heart of the human domain.

He cackled in satisfaction. 'Mission complete,' he thought.

Serika Thornveil's masks rippled, sending phantasms screaming through the ranks to cover their exit. "The seeds of fear are sown," she said with a grin. "They will bleed themselves for years to come."

"They will never forget this event".

Ulfar slammed his molten hammer down, collapsing entire sections of the stands and blocking the onrushing knights as he flashed a bloody grin.

"Let them dig through their rubble, let them dig out the bodies," he grinned evilly. "We're done here."

Major Pain stood bloodied, chest heaving, his Eye of Pain blazing as he tried to pierce Serika's illusions. But the void warped, the smoke thickened, and the Demon Lords vanished, retreating back into shadow.

He couldn't give chase either. Having fought 1 vs 3 for a time before Principal Aelthar came, he was also suffering from grievous injuries.

In the sky, as soon as the 3 Demon Lords escaped, Principal Aelthar's White Flame incinerated entire platoons of lesser demons. The Lords may have already slipped from their grasp, but Demons still remained to incinerate.

Only then did the scale of devastation fully settle.

The stands of the coliseum, once filled with nobles, scouts, and cheering families were now rivers of blood.

Limbs scattered like broken dolls. Guild envoys in scholarly robes lay dismembered, their contracts and scrolls burning to ash. Proud nobles, once laughing at the battles below, now hung in pieces from shattered stone.

Even Nexus Academy's own senior students who came to watch their juniors were dead, their bodies cut down before they could ever rise to glory.

Unlike the applicants, high-ranked Demons targeted them.

Mira covered her mouth at the sight, bile rising in her throat. Kairo stood frozen, staring at the corpses with hollow eyes, fury boiling inside his starved, broken frame. His fists clenched until his nails dug into flesh.

"This…" he rasped, "is what they came for".

But the slaughter wasn't finished.

The demon foot soldiers, though outnumbered now by the tide of reinforcements, suddenly froze. Their crimson eyes flickered.

The human Knights hesitated. "Why did they stop…?"

Then the runes appeared. Crimson glyphs spread across their chests and throats, glowing brighter with every second.

Major Pain's sudden roar split the air.

"BACK! EVERYONE BACK!"

But it was too late.

One by one, then all at once, the demon soldiers detonated!

BOOOOOM!

A chain of hellfire explosions tore through the arena.

Shockwaves flattened entire battalions, and flames swallowed civilians as smoke and screams filled the air. Stone walls cracked and collapsed, burying survivors and corpses alike. The sky itself turned red from the infernal blaze.

Students shielded their faces, ears ringing as the ground heaved beneath them.

When the smoke finally cleared, only devastation remained.

Reinforcements secured the ruins, staggering through flames to gather the survivors. Mages cast barriers to keep the coliseum from collapsing entirely, while healers scrambled from body to body.

The Demon Lords were gone. Their foot soldiers had reduced themselves and thousands of humans to ash.

Major Pain stood bloodied among the rubble, one arm hanging uselessly, his remaining eye burning with fury.

"This wasn't a battle," he growled, his voice carrying across the ruins.

"It was a message!"

Kairo slumped to the ground, body trembling. His stomach gnawed at him, his muscles screamed, but none of it drowned the truth pressing into his skull.

A message carved in blood and fire.

He whispered the words, voice hoarse but steady.

"This is war".