The Protagonist's Sister Is Actually The Strongest

The Heavenly Demon found himself in perhaps his most grueling battle yet. Even when he had faced someone he considered his equal, the Heavenly Empress, or when he had fought and killed a Constellation, he had never encountered such a challenge.

The monster before him was not even from this world, nor was it like the machine-like Constellations. This “being”—or perhaps this “man”—was an entity beyond his world and likely many others.

A king of kings, an absolute force above all Demons, he hailed from another, separate dimension from Bestia—one the Heavenly Demon had only heard about from Anna. He had seen her “tamed” Demons, but they were far weaker and vastly different from the formidable adversary he now faced.

This powerful Demon claimed to be the “King of All Evil.” Beyond his absurd power, his personality was incredibly annoying. He treated the Heavenly Demon as nothing but an interesting little plaything he wanted to turn into his new pet.

It was still unknown how the Universal Computer had even managed to recruit this being. Even among Void Rulers, the King of All Evil was respected. As the creator of the Seven Demonic Thrones and the strongest Fallen Archangel—some even called him “the original sin” or “the original demon”—he wielded immense authority and popularity. He was known across nearly every worldline of Earth, and even Void Rulers seemed wary of him, despite the fact that he was not a Void Ruler… yet.

He stood at the same level, if not higher, as the Heavenly Golden Dragon Emperor. He was the dragon’s opposite. While the dragon was considered an {Original God}, he could be deemed an {Original Devil}, a primordial existence that had shaped the birth of millions of worlds and ruled as the supreme sovereign of all 999 Hells, the home worlds of all Demons.

Naturally, the Heavenly Demon, in his ignorance, had no idea what kind of monster he was truly fighting. Even if he had known, his attitude would not have let him care. This monstrosity was also bound by contracts and could not simply descend into another world even if he wanted to do so desperately. Thus, he had chosen a vessel.

His vessel was the strongest Demon he could summon with his current powers and authority in this world, under the strict conditions and rules set by the Cosmos itself. It did not look anything like his original appearance, but as a cheerful man, he did not care what a vessel—an empty husk for him to use—looked like, as long as it was compatible with his powers.

The Demon had fiery red skin covered in golden tattoos, three black horns growing from his head, long silvery-white hair, and four pairs of black demonic wings, along with a long tail ending in a sharp, stinger-like tip.

Slender yet leanly muscled, he possessed two pairs of arms with sharp black claws and eyes on the palms of his hands, plus another eye on his bare chest. He wore only loose white pants that covered his waist and legs. The handsome Demon, with his golden eyes and flawless face, smiled at the Heavenly Demon with the same hateful, shit-eating grin that had been driving the crow into a fury this entire time.

A few minutes ago, there had been over five thousand Demons here. Now, barely a few hundred remained. None dared to get close, unwilling to interfere in the legendary battle between their supreme king and this powerful, feathered being from another world—a being who, despite not being a Demon like them, still called himself one.

The King of All Evil had become utterly obsessed with the Heavenly Demon. He had asked him several times if he wanted to become his “pet,” something this monster loved collecting. Uroboros, among many others, were all his “pets.” There was a reason most of the Archdemons within the Seven Thrones he had created were beast-like rather than humanoid—he preferred them to be adorable animals, pets for him to look at and care for… or rather, toys.

He had grown rather annoyed when Anna killed Uroboros, his dearest pet—the cutest snake he had ever found and one he had even raised personally. Yet he shed no tears. His fury was like that of someone whose favorite possession had been taken away and broken. They would not cry, but they could become so enraged they would kill the one who had destroyed the precious object they had spent so much effort acquiring.

More than anything, he had come here simply to kill Anna for slaying Uroboros. He could not care less about taking over this world, and even less about its people.

But the moment he laid eyes on the Heavenly Demon, he simply could not let go! Once he asked the Heavenly Demon to become his “pet” and received a punch to the face in response, their fierce battle had begun.

They had been fighting for barely a minute or two, and the Heavenly Demon had already tasted the immense power this mysterious Demon carried. He had sustained tremendous damage: half his beak was broken, one of his wings had been torn off, and all the severed parts were now kept by the Demon inside a red bubble made of demonic energy. The creature was a total freak!

The situation had become truly dire. With Anna, the Heavenly Empress, and his son Song far away, battling other Demons and facing different challenges, the Heavenly Demon had to fight this monster alone to prevent the invasion of Bestia from growing even worse.

If only he could reach the portal the Demon was protecting, he might be able to close it and end this invasion once and for all. It was the last one remaining!

Yet that was becoming more and more impossible. The monster before him would not let him get even an inch closer.

Yeah, he was cornered. Against a foe like this, with the damage he had already taken, most immortals would have already fallen into despair and tried to escape.

But that was not the case for the Heavenly Demon. After all, every bit of damage he sustained was perfect fuel for a masochistic bastard like him who lived for nothing but battling to the death.

“Hahaha! You look rather tired, my dear. How about you take a break? Hahaha!” laughed the Demon. “Ahh! I wonder if I can get that other wing now? Your feathers are so beautiful and silky~!”

The Demon took out one of the bloody black feathers from the bubble he carried, caressing it gently before licking the blood off with his long tongue.

Indeed, he was a total freak!

“Hah, you fucking bastard…” The Heavenly Demon smiled back at him, eyes burning with rage. “You haven’t even seen everything I can accomplish yet. Don’t go calling victory so soon.”

“Hoh? I have analyzed you a couple of times already, from top to bottom. There is nothing else you are hiding. The cosmic power you carry was indeed rather interesting, but it is still from some low-level Constellation—barely anything,” the Demon shrugged. “Come on, do you want me to continue tearing you apart piece by piece, or will you willingly become my pet? I swear I will treat you with care! Hahahah!”

“Fucking bastard…! YOU’LL SEE!”

The temperamental Heavenly Demon finally lost all patience. His powers erupted from his body in immense waves of energy.

The power the King of All Evil had expected to be mostly depleted suddenly refilled itself out of nowhere. The Demon realized this crow gained strength through negative emotions and the damage inflicted on his body.

“Interesting! So you’re that type of fighter. Then this is—”

“{Seven Demonic Cursed Seals}: {Full Release}!”

RUMBLE!

“Hm?!”

The Demon’s eyes widened as he felt a tremendous surge of evil power exploding from the Heavenly Demon. Indeed, he was channeling his evil power, not the inner peace he had achieved before. Despite his previous change and enlightenment, the dark side of him had never left.

If anything, both sides of him now lived together, complementing each other through their powers. After all, despite everything, he would never abandon who he truly was or the path he had walked until now.

By merging the two paths, he had created a perfect balance—a new power that even the Heavenly Demon had never tapped into before, because of his reluctance to ever regret any of his decisions.

FLASH! FLASH! FLASH! FLASH! FLASH! FLASH! FLASH!

All seven seals activated at once, releasing bright flashes of red and purple light that glowed beneath his black feathers. The Heavenly Demon tore off his clothes, revealing his muscular, feathered chest now fully covered by the glowing cursed seals.

Each seal released a different-colored mystical flame of evil power—a powerful negative emotion he had infused into his body for many years. These evil flames, made of Demonic Ki, merged into his chest and converged into a single core of deep darkness.

In that moment, the Heavenly Demon stepped into a realm beyond anything he had ever reached before!

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