The Protagonist's Sister Is Actually The Strongest

“{Heavenly Seal}!”

Using the particles of light, ki, and other energies released by the explosion, Anna transformed them into giant chain-shaped runes that wrapped tightly around the portal.

“Greeeaaagh!”

“Gryyeeeh!”

“Shaaaahh!”

The insectoid demons lunged forward again, grasping the chains and shaking them violently in their desperation to break through. Their hands burned on contact, turning to ash as they recoiled in agony.

“There! Done! Things are too chaotic to deal with another problem right now!” Anna declared. “I’ve temporarily sealed it. It should hold for at least half an hour; that will give us enough time to handle this situation.”

“Please explain what’s going on!” her adoptive father grumbled, frustration evident in his voice.

“Hah, long story short, I have some enemies back home—let’s say three otherworldly demons whose power surpasses all the constellations we’ve fought combined,” Anna replied with a calm, straight face.

“EH?!”

Her entire adoptive family stared in stunned disbelief. Anna had rarely spoken of her many enemies, and this sudden revelation made the situation feel even more overwhelming.

“It seems the Void Ruler behind this—the Universal Computer—formed some sort of pact with them and brought them here. But I believe this is their last resort. We need to act quickly: eliminate the remaining machines, destroy the catalysts, and then find a way to fend that thing off,” Anna explained.

“How can we stop the demon invasion?” Song asked urgently.

“We’ll close the portals to prevent more demons from coming through and destroy their catalysts,” Anna answered, her gaze fixed on Beelzebub. “That nasty fly is one of them. But I detect two more large portals, which means there are two other catalysts. We’ll have to split up and take them out. Song, choose who you want to accompany.”

“I’ll go with Mom then!” Song decided quickly. “She didn’t absorb the cosmic power like Dad did, right? So she’s still weaker.”

“Hah… Well, I was a bit arrogant in rejecting such strength, but thank you,” his mother said with a warm smile. “I appreciate the help, my son.”

“Fine then! I’ll go alone! Not like I need my son’s help or anything!” the Heavenly Demon grumbled.

“You girls, accompany them!” Anna’s Myriad Self Aura split into several Egos. Six of them emerged—three joined her mother and Song, while the other three moved to support her father.

As this unfolded, she cast a quick glance toward Beelzebub.

“Young Lady, I am ready for battle at any time!”

Fang Shuan’s voice echoed clearly in her mind. She was currently fused inside his mechanical body, merging her powers with his to transform him into an imposing mech.

Sepa and Bastet had also integrated into his form, amplifying his strength further. Using the Mighty Morphin Core, they unleashed power reminiscent of the King of Steel.

“Anna, let’s finish that bastard off once and for all!”

Sepa sounded fiercely determined.

“Indeed. It’s time for him to meet his ultimate end.”

Bastet’s voice carried rare bloodthirst.

“If I could already kill two Constellations, then taking down this damn fly shouldn’t take long… Let’s do this.”

CRAAASH!

RUMBLE!

The Demon King and Beelzebub collided with tremendous force, their blows clashing violently. Without Song’s soul, the Demon King had grown noticeably weaker. Although being named by Anna had restored some of his power, at least half remained lost.

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Even so, it was still overwhelming. The worst part for Beelzebub was that the longer they fought, the more the Demon King learned. Like a machine, it possessed incredible adaptive ability, rapidly memorizing every movement, evading them, and predicting what came next.

At the same time, Nemesis was evolving swiftly. Its old and new abilities were being rediscovered and refined in the heat of combat.

Beelzebub had unwittingly become the perfect training partner for Anna’s new companion, and she felt a quiet gratitude for that irony.

“DAMMIT, THIS THING!”

Beelzebub swung all six of his gigantic, armored claws. His body now towered over a hundred meters tall, yet the Demon King stood several dozen meters higher. Both of its enormous arms were massively bulky and harder than any metal Beelzebub had ever encountered.

His claws couldn’t even pierce Nemesis’s armor. Instead, they cracked and threatened to shatter into fragments. Demonic power surged through his body, allowing him to regenerate the damage almost instantly.

“You’re one annoying bastard, aren’t you?!”

Beelzebub gritted his sharp jaws. He swung his claws upward and downward—not to strike, but to evade the barrage of laser beams fired from cannons Nemesis had generated.

As the giant fly dodged countless explosions with astonishing agility, he continued moving his claws. Hundreds of demonic runes formed in mere seconds, converging into a massive demonic pentagram.

FLASH!

Then, with all his strength, he shot forward in a blur of black and red. The Demon King’s heavy body couldn’t track him fast enough. Beelzebub slipped behind it.

“{Black Cross of Pestilence}!”

FLAAASH!

A colossal black cross erupted from the pentagram and pierced straight through the Demon King’s body. Though it dealt no visible physical damage, the Demon King’s eyes widened in sudden, excruciating pain.

An electrifying agony coursed through its form. The deadly black cross unleashed a curse that shocked its entire being. Green fog rapidly manifested, wrapping around it and sapping its strength.

The Demon King swung its claws at Beelzebub, but its movements had grown sluggish. The fly evaded effortlessly and smiled with vicious satisfaction.

“Heh! You’re slow now, aren’t you? You might be stronger physically, but when it comes to Demonic Magic, nobody can surpass me!”

“RAAAAAHH!”

The Demon King roared in fury and manifested two massive mechanical arms from thin air. Unhindered by the Black Cross of Pestilence, they smashed toward Beelzebub from both sides.

CLAAAASH!

“GIIEEGH?!”

Beelzebub let out a pathetic groan. He was shocked that the Demon King could still fight so fiercely. His own body had become incredibly tough and powerful, yet the overwhelming might of a Demon King remained a step ahead—even in its weakened, hollow state.

“T-This damn bastard is still this strong?!” Beelzebub thought, gritting his mandibles as he poured power into all his limbs. He pushed outward with desperate force, muscles tearing and breaking only to regenerate moments later. “I cannot let him get me! I may be weaker, but I possess a gigantic quantity of Demonic Energy thanks to my sponsors! I won’t lose!”

While four of his arms shoved the two massive mechanical palms away, his remaining two finished conjuring a triple-layered demonic pentagram.

“{Red Sword of Starvation}!”

CLAAASH!

“GRRRH?!”

The Demon King vomited black, miasma-like blood as a giant red sword pierced its chest in an instant. A red cloud enveloped it, rapidly draining its energy and nutrients.

But Beelzebub was not finished.

“{Green Axe of Agony}!”

A massive green axe formed from strange, slime-like energy swung down, severing the Demon King’s left arm completely.

SLAAASH!

“GRAAAAAAHHHH!”

The Demon King screamed in torment, its powers destabilizing further.

“Heh… Ugh…! And now…!”

Suddenly, a blue scythe materialized above Nemesis, glowing with the pure aura of…

Death!

“Your body will be mine… And once I obtain it… I will become the strongest demon!”

Beelzebub laughed triumphantly as the scythe descended.

“{Blue Scythe of Death}!”

The scythe spun faster, gathering immense force as it hurtled toward the Demon King’s head—aiming to behead him and leave his body vulnerable for takeover.

“YOUR BODY IS MINE!!!”

Beelzebub already believed victory was his. His laughter echoed across the skies as the scythe—

“{Heavenly Myriad Blade Arts}: {Golden Dragon Descent}!”

”ROOOAAARRR!”

Beelzebub’s eyes widened in horror as a gigantic golden dragon erupted from below. It opened its jaws wide and devoured the blue scythe, shattering it into fragments.

Crack, crack…!

CRASH!

The golden dragon surged forward, still trapped between the Demon King’s mechanical fists, and charged straight at Beelzebub.

“W-wait a second—AAACK!”

SLASH! SLASH! SLASH! SLASH! SLASH!

The powerful swordsmanship technique engulfed Beelzebub completely. As the dragon devoured him, thousands of slashing attacks tore across his body in an instant. Then the accumulated force detonated in a massive explosion.

BOOOMMM!!!

“W-What the…?!”

Beelzebub plummeted from the sky, his eyes wide with disbelief at the sheer devastation. More than half of his gigantic body had vanished.

What remained was only his torso, two left arms, and half his head.

His insectoid eyes turned toward Anna—or rather, toward the colossal machine she piloted, fused with her power.

“How did she become so powerful in such a short time?!”

The gap between the Anna he had fought before and the one before him now was like heaven and earth.

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