The Protagonist's Sister Is Actually The Strongest

Lucifer was under attack from every angle. The Heavenly Empress unleashed powerful palm strikes followed by masterful swordsmanship techniques, relentlessly driving him back with her newly enhanced Heavenly Imperial Armament Mechanical Armor.

Meanwhile, Song channeled the power of the Heroic Heart of Will, delivering a barrage of blazing punches infused with his massive Battle Aura. Following the techniques his father had taught him, he drove the giant seven-headed dragon back and forth.

RUMBLE!

“TCH! RAAAAHHH!”

Lucifer grew desperate and unleashed seven gigantic breath attacks at both of them. The blasts pursued them as they tried to evade, relentlessly targeting their every move.

“Song! Come to me!”

The Heavenly Empress called to her son. The boy swiftly flew to her side. In that instant, she waved her hand and manifested a colossal golden shield. She stood firm as all seven breath attacks slammed into it.

BOOOMMM!!!

Crack, crack…!

The shield began to fracture, yet it held against all seven attacks at once. Lucifer stared in stunned disbelief, his seven heads brimming with frustration.

“Y-YOU THINK THAT SHIELD WILL BE ENOUGH?!”

An eighth head suddenly emerged from his torso, jaws gaping wide to reveal thousands of razor-sharp fangs and a writhing tongue.

With a monstrous roar, a titanic breath attack of pure demonic energy surged toward the Heavenly Empress and her son.

“Reversal!”

She swiftly released the damage absorbed by the crumbling shield, countering with an equally massive beam of light that collided with Lucifer’s desperate attack.

RUMBLE!

As the skies quaked from the clashing beams of demonic energy and ki, the Heavenly Empress and Song seized the opening. They darted toward Lucifer from below.

At the same moment, a giant mechanical fist slammed into Lucifer’s backside, hurling him forward with tremendous force.

BAAAM!

“Ugh?!”

He glared back in fury and locked eyes with the colossal Fifth Demon King, Nemesis. Unlike the others, Nemesis faced him head-on, showing not a trace of fear.

“YOU DAMN PIECE OF SHIT!”

Lucifer lunged downward, jaws wide, and bit into the mechanical Demon King’s body. The Demon King roared furiously with a metallic voice. It opened its massive jaws and unleashed an explosive beam of photon energy directly into Lucifer’s face.

BOOOM!

“AARRGH!”

Lucifer screamed in agony as a gaping hole tore through his eighth head. Most of its upper jaw was obliterated, and blood gushed everywhere.

“Y-YOU DAMN…!”

He swiftly extended his giant draconic arms and conjured thousands of enormous demonic pentagrams—magic circles unique to demons.

“{Endless Infernal Meteor Rain}!”

Roaring with boundless fury, the King of All Evil bombarded Nemesis with countless explosive meteors, striking the demon’s body without mercy.

BOOM! BOOM! BOOM! BOOM! BOOM!

“GRUUUAAAGGGHHH!”

Nemesis tried to push through with raw physical strength but faltered as Lucifer laughed maniacally and continued his relentless onslaught.

Each meteor exploded against the Demon King’s face, melting its metallic body and driving it downward with crushing force.

“The Demon King was tamed by Anna, and he’s putting his life on the line for our sake now…!”

The Heavenly Empress glanced at the Demon King. Even as half its body melted, it kept roaring and fighting like a relentless beast on the verge of death.

Though her son stood by her side, that monster had been forged from his body. Even with his soul now secured, that being remained a part of Song.

“Mother, now!”

Song knew exactly what his mother was thinking and why she hesitated to coordinate with Nemesis.

But there was no time for hesitation.

“I know what you must be thinking, but he’s our ally now. We have to fight together, or we’ll never avenge my father’s death!”

“That’s right…! I’m sorry, Song! Let’s do this.”

The Heavenly Empress and her son surged toward Lucifer like a golden and a red star, striking his body from both sides.

“{Twin Star of Hope and Will}!”

Their auras converged, unleashing a combined technique reminiscent of the one the Heavenly Empress had once performed with the Heavenly Demon.

CRAAASH!

Lucifer vomited torrents of blood as cracks splintered through his soul. He looked down at the massive hole piercing his heart and lungs.

“D-Dammit…! FUCKING… DAMMIT!!!”

His wounds resisted regeneration. He mutated further, sprouting grotesque tumors of flesh and bone to replace the lost tissue. His original vessel twisted and warped into something unrecognizable.

“GRAAAAHHH! I WON’T DIE UNTIL I MAKE SURE I KILL YOU ALL!!!”

Lucifer’s fury consumed him. His monstrous draconic form sprouted long, scaled tentacles resembling dragon tails and countless additional heads, transforming him into an eldritch abomination.

“DIE! DIE! DIE! DIE! DIEEEE!”

His heads roared the same words endlessly, driven mad as his sense of superiority shattered before these “lowly mortals” who defied all logic.

Space and time warped around his body. The Heavenly Empress and her son stared in disbelief at the aberration before them.

As if the entity controlling the machines wasn’t enough, it had summoned such an abomination into their world.

“Let’s do this, mother!”

“My son… You’ve truly grown so much…”

The Heavenly Empress gazed at her son, radiating confidence. For a moment, she glimpsed the shadow of his father behind him. With every battle, he grew to resemble him—not as he once was, but as the incredible hero who had sacrificed himself for a world he once despised.

Through hope and family, he had learned to love it, becoming someone so extraordinary that, in his final moments, he even surpassed her.

“This is a monster beyond all our expectations. We can’t hold back, alright?”

FLUOSH!

“Yes, I understand, Mother!”

Their auras merged, golden and red hues intertwining, erupting into flames that formed a massive phoenix-like battle aura behind them.

“{Heavenly Phoenix of Hope and Will}!!!”

The two roared and charged at Lucifer with the colossal phoenix at their backs. An explosion of flames engulfed half of his aberrant body.

BOOOMMM!!!

Lucifer screamed in agony. The flames burned him relentlessly, making regeneration nearly impossible as he squirmed and distorted the space around him, desperately trying to open more Demon Gates.

“STOP!”

As Song and his mother shouted furiously, the giant phoenix cried out. It swung its sharp talons and tore apart several of the draconic king’s heads, disrupting his focus.

“B-BASTARDS…!”

Lucifer gritted his myriad sharp teeth. His body continued mutating as massive, muscular arms and fists sprouted across his fleshy form, unleashing a barrage of punches and explosions of demonic flames.

BAAM! BAAM! BAAM!

The phoenix was swiftly overwhelmed and reduced to nothing. It exploded into pure energy, blinding Lucifer and pushing him back.

BOOOM!

“MY DEMONS…! MY DEMON ARMY! COME TO MEEEE!”

In a desperate act of frustration, Lucifer pierced his own flesh and soul with his hands, opening a massive, blazing demon portal within his aberrant body.

FLUOSH!

“W-What…?!”

“That bastard could do something like that?!”

Countless demonic hands and monstrous beasts poured out of the hole in Lucifer’s body, overflowing with demonic energy and constantly warping the space around them.

“ROOAAARR!”

“GRYYAAAH!”

“SHAAAAGH!”

Their incomprehensible roars revealed their true nature. These were no ordinary demons, but something far worse—Demonic Beasts forged in the brutal environment of the 999 Hells.

“KILL EVERYTHING! DEVOUR EVERYTHING! THIS WORLD IS OURS TO PLUNDER AND BURN!”

“I WON’T LET YOU!”

“THIS WORLD IS NOT YOURS!”

Mother and son roared back. Their auras swelled to tremendous size, enveloping their surroundings and distorting reality itself.

“{Double Domain: Heavenly Cage}!”

FLAAASH!

They conjured a powerful Domain out of nowhere, trapping Lucifer and the Demonic Beasts inside. It bought them precious time as they rushed through the horde, cutting the beasts down one by one.

“Just when will this end?! This damned monster…! I cannot let my husband’s death be in vain! There must be a way!”

The Heavenly Empress swung her katanas, slicing through countless Demonic Beasts. Their bodies exploded upon death, constantly harming her.

BOOM! BOOM! BOOM! BOOM!

“Uggh…! Dammit! This is ridiculous!”

She glanced at Song, who was being overwhelmed by dozens of Demonic Beasts at once. Her eyes widened as she rushed to save her son.

“SONG!”

However, more Demonic Beasts emerged—aberrant wolves, tigers, lions, rhinoceroses, and chimeras of various beasts and monsters. Typically covered in red, black, or orange fur, they bristled with horns, spikes, extra eyes, limbs, and wings.

The smallest stood over fifteen meters tall, while the largest reached fifty meters. The Heavenly Empress had no trouble slaying them, but their sheer numbers made movement difficult, let alone dodging their blows.

Things looked dire once more, and yet…

“GRAAAAHHHH!”

The mighty Fifth Demon King continued fighting fiercely, giving his all.

-----