The Devourer Within Naruto's World

In the dark depths of an underground hell, there stood a demon king named Kai, who had ruled the netherworld for decades. But he hadn't always been a demon. Once, he was a simple man on Earth, living a quiet life. His death had brought him to hell, where his soul should have faded into the background like countless others. Yet, something within him awakened. Driven by an unquenchable hunger for power and survival, he clawed his way to the top, defeating those who stood in his way. Over time, he claimed the title of Demon King, molding the chaotic underworld into his domain.

Kai now sat on his twisted throne, built from the bones of fallen demons. Before him, chained and beaten, was the last of the seven deadly sins—Wrath. The embodiment of anger, resistance, and rebellion, Wrath had been a thorn in Kai's side, leading uprisings and daring to challenge his rule. But now, Wrath was broken, handcuffed and too weak to fight back.

Kai leaned forward slightly, his cold eyes narrowing as he regarded his fallen enemy. "Any last words?" he asked, his voice a low rumble that echoed through the cavernous throne room.

Wrath's bloodshot eyes glared back at him, the fire of anger still burning within despite his defeat. With a guttural growl, Wrath used the last of his strength to snap open the handcuffs, lunging toward Kai with a desperate attack.

Kai didn't flinch. He raised his hand lazily and blocked the attack with ease. Then, with a single word, he sealed Wrath's fate.

"Devour."

Instantly, Wrath's body began to wither. His once powerful frame shrank and aged, his muscles dissolving into frail bones as though his very essence was being sucked away. Kai stood there, watching with a smile as his enemy was drained of life, reduced to a hollow shell of what he once was.

"Ahh... Nourishment..." Kai murmured, feeling the surge of power course through his veins. His body glowed faintly as the essence of Wrath flowed into him, feeding the darkness inside.

A soft chime echoed in the air.

Ding.

Kai glanced at the glowing interface that only he could see, the system that had been with him since he arrived in this realm. A notification blinked.

Level up. You are now Level 99.

Kai smirked. He was one step closer. Closer to what, he wasn't sure. But with every soul he devoured, with every rebel he crushed, the void within him only seemed to grow. The higher he climbed, the more meaningless it all felt. The Netherworld, this throne, the power—it had all begun to taste hollow.

Ruling the underworld had once been his ambition. But now, a deeper hunger gnawed at him. He didn't just want to rule hell anymore. He wanted to break free of it. To destroy everything—the Netherworld, Heaven, Earth—all of existence. Nothing deserved to continue if this was all there was.

With each level, Kai grew stronger, but the emptiness inside him expanded. He believed now that his fate was to end it all, to bring destruction to every plane of existence.

And when it did, there would be nothing left.

One of Kai's most loyal commanders, Frankenstein, approached him with a rare gleam of excitement in his eyes. A towering figure with a patchwork of scars and stitches crisscrossing his face, Frankenstein had been Kai's most trusted advisor for centuries, responsible for countless innovations in dark magic and twisted alchemy.

"My lord," Frankenstein began, bowing deeply. "It appears we have successfully developed the teleporting crystal. However…" he hesitated briefly, "the process requires immense resources. As it stands, only one person can use it, and it will take another five years to create another."

Kai's interest piqued, and his gaze locked onto the crystal Frankenstein held. With one swift movement, he plucked it from his commander's hand, inspecting it closely. The small crystal pulsed with dark energy, swirling with the promise of power and escape.

"How sure are you that this will take me to Earth?" Kai asked, his voice calm, yet laced with dangerous anticipation.

Frankenstein nodded confidently. "One hundred percent, my lord. We've refined the calculations. It will open a direct gateway to Earth, as you requested."

Kai's eyes narrowed slightly, as though weighing his options. "And how do I activate it?"

Frankenstein bowed again, eager to please. "You simply have to break it, my lord."

For a moment, silence filled the air as Kai stared at the crystal in his hand. Then, without warning, he drew his sword in one fluid motion and plunged it into Frankenstein's chest. The blade slid through his flesh effortlessly, and with a gasp, the commander collapsed to the ground, his body twitching in surprise.

Kai looked down at him without a trace of emotion. "You've done well, Frankenstein."

Frankenstein's eyes widened in disbelief, but his body quickly went still, leaving only Kai and the dim glow of the crystal in his hand. He turned away, his mind now set on his next move.

With a single powerful thought, Kai flew up into the dark skies, rising above his sprawling empire of twisted demons and forsaken souls. He hovered there for a moment, gazing down at the world he had conquered. His once-mighty empire had been built on the suffering and submission of countless beings, but now… it was enough.

"It has been a long time," he murmured, his voice carrying through the air, "but thus, all shall fall under me."

Closing his eyes, Kai summoned the dark essence of Wrath—the very soul he had devoured moments before. A violent red aura erupted around him, swirling like a storm. The power of Wrath surged through him, raw and uncontrollable, until the air itself crackled with malevolent energy.

Then, with a mere thought, Kai unleashed the full force of his fury.

A deafening explosion of crimson light burst from his body, spreading out in all directions like a nuclear blast. The red energy consumed everything in its path, burning through his empire, reducing it to nothing but ash. Towers crumbled, demons disintegrated, and the very ground itself cracked under the weight of his power. The netherworld was engulfed in flames as his destructive wrath obliterated all that he had once ruled.

Kai stood in the center of the destruction, his heart cold and still as he watched the world burn. Everything he had built, everything he had fought for, gone in an instant. With but a thought, a voice rang out throughout the world, "The world's politic is dead, be independent, survive and depend on each other based on your own strength and needs."

He then looked down at the teleporting crystal in his hand, the final key to his plan. With a smile that held no warmth, he crushed the crystal in his fist.

In that moment, his very essence—his soul, his power, his being—disappeared from the netherworld, vanishing into the void between realms.

And with that, Kai was gone, leaving only ruin in his wake.