The Protagonist's Sister Is Actually The Strongest

Astaroth’s eyes widened. Despite the thousands of years they had known each other, the words still echoed in his mind.

“You have my back, and I have yours…”

Aim had never forgotten the day Astaroth said that.

“Aim…!”

Without warning, Astaroth burst into tears and pulled Aim into a tight embrace.

“Let me go, you fucking piece of shit! Agh! Oi! Look! Lucifer is coming! Hey! We have to do something, you dumbass!”

“We’re friends! Friends!”

“Agh! I swear, I should’ve killed you back then!”

As Aim began to regret every corny thing he had ever said…

“That was love in its purest form. How beautiful. To think even demons can feel love.”

“{Heavenly Myriad Blade Arts}”

SLASH! SLASH! SLASH! SLASH! SLASH!

“UGH?!”

“Huh?!”

“W-Wha…?!”

In that instant, Lucifer, Astaroth, and Aim all looked skyward as a rain of pink slashing flames tore through Lucifer’s heads and arms in the blink of an eye.

“{Loveless Slash Assault}”

As Lucifer was ripped apart, the trio turned toward the source of the attack. Her eyes glowed bright pink, hearts shimmering within her blazing pink-and-gold aura.

And then—

BOOOM! BOOOM! BOOOM!

Countless explosions erupted around her. The Demonic Beasts were hurled back, burning with pink flames, while tumor-like growths burst across Lucifer’s body.

“Ugh! What is this agonizing pain?!”

As Lucifer screamed in utter horror, the one responsible for his torment appeared before Aim and Astaroth—protecting her former enemies.

“Love is far more complex than you imagine, Lucifer. It is an emotion that connects us all. Why does it hurt so much, you ask? Because this technique inflicts greater damage and pain the less love you feel for others—or even for yourself. And it looks like you’ve got plenty of issues you don’t want to face, huh?!”

“Anna! You damn...! Wait, where’s Legion?! LEGION!”

Lucifer’s eyes widened as hundreds of gigantic arms materialized above him and slammed down with crushing force.

BAAM! BAAM! BAAM!

Lucifer was smashed downward into the ocean, sending massive ripples surging across the water.

“Legion doesn’t answer to a tyrannical king anymore, Lucifer! He’s my new ally now, right?”

“OOOOHHHH!”

Legion wasn’t one for words, so he simply let out a thunderous groan, countless voices echoing within it.

The truth was that, like the Demonic Beasts, Legion had not been born this way—he had been created by Lucifer. Anna had discovered it quickly when she read his soul and witnessed his memories. He carried the connected memories of hundreds of demons Lucifer had tortured and stitched together into this abomination.

“Legion…! That’s… Wait, Master Anna! You saved us!” Astaroth cried joyfully, carrying Aim in his claws.

“Let go of me!” Aim snapped, breaking free and feeling strangely flustered. “Master! You’re back—and is that Legion?!”

“Yes, I’ve recruited him into the team. Say hi to your new junior~!” Anna winked, smiling with greater confidence than ever before.

“A-Ah… Hi…” Aim’s eyebrows twitched as the monstrous being stared at him with its countless arms. “Oh wow… I never thought this could happen. But Centurion and Morox… Well, I guess those bastards don’t matter anymore.”

“Anna!” The Heavenly Empress called out to her.

“Coming!”

Anna nodded, her expression turning serious, then vanished in an explosion of pink, heart-shaped flames. She reappeared before her master and adoptive mother like a pink-and-gold blur.

“{Heavenly Myriad Blade Arts}”

Her eyes shone with dazzling light as her aura surged with unprecedented power.

“Anna’s aura… It has grown so strong?! This is… She’s constantly evolving!”

“{Blazing Loving Embrace}”

SLASH! SLASH! SLASH!

Dozens of Demonic Beasts surrounding Anna and her mother were sliced apart by pink flames and blades. Then—

POOF! POOF! POOF!

Their monstrous bodies dissolved, and smaller demon people fell from them, unconscious.

“I knew it… They weren’t true monsters this entire time…!”

The Heavenly Empress had sensed something strange about these creatures, but the desperate situation had forced her to slay them regardless.

“Don’t blame yourself, Mother. You didn’t know… Even now, their souls are so corroded that I’m not sure they’ll ever wake up.”

Anna’s Purgatory expanded into dozens of portals, catching every demon she had restored and carrying them safely into her Demonic Realm.

As this unfolded, her own demons reached her, with Song right behind them.

“So you’re back, Master,” Bael said.

“CRAAH! About damn time!” Neberius cried.

“What took you so long—LEGION?!” Agares exclaimed in shock.

“M-Master, please let me go back to the Realm! I’m so scared! I wasn’t made for these large-scale battles!” Jeremias sobbed. As an artificial demon spirit, he was utterly unprepared for any of this.

“Sorry, Jeremias, but you’re strong. I need you to fight alongside everyone else, alright?” Anna asked gently.

“Anna! You’re back! Thank the heavens!” Song hugged her tightly. Anna patted his head and kissed his forehead.

“Yeah, don’t worry too much about me, little brother,” Anna smiled. “I’ll always come back.”

“Hahah! Such arrogance. You really do act like your father sometimes, huh?” The Heavenly Empress let out a soft laugh.

The moment she arrived, the entire atmosphere shifted. The despair that had weighed on them vanished. Anna changed everything—always. There was something magical about her that soothed hearts and united everyone more strongly than before.

RUMBLE!

The seas trembled violently as something enormous rose from the depths while Anna spoke with her mother and brother.

SPLAAASH!

“ANNAAAAAAA! I’LL DEVOUR YOUR DAMN SOUL NO MATTER WHAT!!!”

The entity that emerged was, of course, him—Lucifer. His monstrous body had taken on draconic and kraken-like traits. While underwater, he had devoured hundreds of oceanic martial beasts, assimilating their mass in a desperate bid for power. Yet even now he struggled to hold himself together.

Could he even still be called a dragon?

Well, he did have scales, so Anna had faith.

“Alright, buddy, time for you to finally have a good meal… Let’s hope you don’t get a stomachache, though.”

Anna gazed at her precious blade—the one that had started her entire journey—Gram. He still seemed to be sleeping, but his aura responded to her.

FLUOSH!

Black and white auras surged from the blade, enveloping Anna completely, merging with her own power and forming countless golden and pink dragon heads that roared and coiled around her.

“He’s hungry…!”

Anna smiled, a flicker of happiness crossing her face. Her friend was still holding on.

But time was running out before he fell into eternal sleep. It was now or never.

“Anna, the only way to defeat him is by attacking together,” her mother said, eyes shining as she gripped her katana.

“Yeah…” Song nodded. “He has a very strong protective layer of demonic energy around his core… If we can shatter it, then…”

“We’ll detach his power from this avatar and send him back to whichever godforsaken hell he came from,” the Heavenly Empress finished.

“That’s a good plan,” Anna nodded. “But we can make it even better.”

Anna smiled and flicked her fingers.

FLAAASH!

Aim and Astaroth began floating upward, their auras merging.

“You two will help us do something even crazier to Lucifer—so combine!”

“We’re fusing?!”

“W-Wait…! Wait a second!”

Astaroth and Aim screamed as their bodies fused into a gigantic demon unlike anything seen before: a golden dragon covered in crackling lightning, adorned with leopard-like markings across golden scales, six powerful arms, and massive fur-covered wings.

“T-This power…! It’s incredible!”

Astaroth and Aim had become an even stronger demon.

“They fused?!” Neberius asked. “CRAAAH?!”

“T-That’s insane…” Jeremias whimpered.

“Yeah, and you guys are fusing too! Let’s kill Lucifer right here, right now!” Anna declared.

Her power flowed outward as the demons began merging—limited to two per fusion.

Neberius and Agares combined into a giant black knight with crow-like armor, four black wings, and a powerful shadow sword.

Jeremias and Bael fused as well, forming a tall, muscular, red-skinned demon with an impish face, clad in black and red armor, wielding a staff topped with a Rubik’s Cube.

Finally, Anna merged Legion and Nemesis, creating a giant bird-faced mechanical goliath with hundreds of mechanical arms extending from its back.

Each fusion radiated tremendous power like never before.

“I know it’s shocking but get used to your new forms quickly. He’s coming!”

As Anna finished her preparations, Lucifer charged straight toward them.

“I’LL KILL YOU ALL!!!”

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