The Greatest Assassin Gets Reincarnated in Tensura

A single second.

That's all it took.

One moment, the vast army of demons stood in the depths of the Underworld, engulfed in its eternal darkness. The next, they were standing beneath an unfamiliar sky, the weight of an entirely different world pressing upon them.

A disorienting silence followed.

Some demons staggered slightly, their senses struggling to adjust. Their eyes darted around, taking in the towering trees, the thick, mist-laden air, the strange hum of life that was so foreign compared to the abyss they had always known. The Jura Forest was unlike anything they had ever set foot in.

But something was off.

There was… nothing.

No structures. No city. No domain of power.

Just a dense forest stretching endlessly before them.

A murmur spread through the ranks.

"Where are we?" one Greater Demon whispered.

"This is supposed to be our new base?" another muttered, his deep red eyes narrowing in confusion.

A few Archdemons cast wary glances at Arion, as if questioning whether they had been tricked. Even Noir and Blanc were momentarily perplexed.

Then, without a word, Arion raised his hand and snapped his fingers.

Reality itself unraveled.

—---

The illusion shattered.

Like glass breaking away from a hidden masterpiece, the magic concealing the Eminence of Shadow dissolved into nothingness, revealing the city in all its dark majesty.

And in that moment, every single demon in the army—Noir, Blanc, the Archdemons, the Greater Demons, the Lesser Demons—froze.

Their eyes widened, their bodies stiffened, and for the first time in countless years… they felt awe.

The Eminence of Shadow.

The City of Eternal Night.

A kingdom sculpted in darkness, yet glimmering with an ethereal beauty unlike anything the Underworld had ever known.

Towering black spires stretched toward the sky, their jagged forms resembling fangs piercing the heavens. Dark crimson light pulsed through veins of glowing runes etched into every structure, casting a ghostly illumination over the streets below. The architecture was both ancient and impossibly advanced, a fusion of abyssal grandeur and eldritch design—a realm where shadow and power intertwined seamlessly.

At the center of the city, rising above all else, was the Obsidian Citadel.

An immense fortress carved from what seemed to be pure void, its surface absorbing light rather than reflecting it. At its peak, a massive throne-like structure rested beneath a sky filled with swirling nebulae of darkness and eerie stars that shouldn't exist in this world.

The streets of the city were vast and expansive, yet eerily silent—as if waiting.

Waiting for its new inhabitants.

The air itself was thick with an overwhelming energy, far beyond what even the Archdemons had ever experienced. It was as though the city was alive, breathing, watching them with unseen eyes.

—---

The reactions came slowly.

One of the Greater Demons stumbled backward slightly, his breath shaky. "This… this isn't possible."

Another whispered, his voice trembling, "What… is this place?"

An Archdemon clenched his fists, trying to suppress the involuntary shiver that ran through him. "This power… This city…" He turned to Arion, his eyes burning with an unfamiliar mixture of fear and reverence. "You created this?"

Noir himself had taken a step forward, his usual calm demeanor slipping slightly. His crimson eyes gleamed as he observed the Obsidian Citadel, his sharp senses detecting something beyond comprehension emanating from within.

"…This place," Noir murmured, more to himself than anyone else. "It's not just a city."

Blanc, who had seen countless realms in her time, found herself at a rare loss for words. Her violet eyes scanned the towering spires, the eerie lights, the abyssal beauty that seemed both inviting and terrifying. A slow smirk crept onto her lips, though it couldn't fully mask the astonishment in her gaze.

"I see now…" she said, her voice carrying an almost reverent amusement. "You weren't exaggerating when you said you had a base."

Arion stood in front of them all, silent and still, his golden eyes watching their reactions with a hint of satisfaction.

Then he finally spoke, his voice smooth yet absolute.

"This is your new domain."

The demons turned to him, still struggling to fully process what stood before them.

"This city," Arion continued, his tone carrying an undeniable authority, "was not built in the Underworld, nor was it shaped by mortal hands. It is a living entity, forged from shadow and will. It exists between realities, a fortress unseen by those who do not belong."

A slow smile crossed his lips.

"It has waited for you."

Silence.

Then, one of the Archdemons—one of the most powerful and prideful beings among them—took a step forward. He was massive, his body clad in shifting black armor, his aura one that had once terrorized the battlefields of the Underworld.

He knelt.

A demon of his stature, kneeling in absolute submission.

"This…" His voice was low, reverent. "This is beyond anything I have ever seen. I swear myself to this kingdom. To you."

One by one, the other demons followed.

The Greater Demons, the Archdemons—each and every one fell to one knee, their heads bowed, acknowledging not just the power before them, but the reality that they now served something greater than even the darkest nightmares of the Underworld.

Noir and Blanc leading them, they all said in unison "we swear our eternal loyalty to you lord Arion."

Arion stood before his new army, his golden eyes glowing with a power beyond comprehension. The silence that stretched between them was thick with tension, with disbelief. Every demon present knew the dangers of naming.

Over a thousand demons, including Primordials and Archdemons.

Arion said "I will name you all."

The sheer weight of such an act was incomprehensible. Naming even a handful of demons had been known to drain even the mightiest beings to death.

And yet, Arion stood there, completely unfazed.

He smirked, an expression not of arrogance but of absolute, unwavering confidence.

"Do not worry," his voice cut through the murmurs like a blade of absolute authority, "it will not cause me any harm."

A moment of silence.

Then, his eyes locked onto Noir.

"From this day forward, you shall call yourself Diablo."

Noir barely had a second to process the words before it happened.

A surge of power exploded from within him, a maelstrom of abyssal energy so intense that the very air around him twisted and burned. The ground beneath his feet cracked and shattered, unable to withstand the sheer force of his evolution.

His entire body was engulfed in a black and crimson inferno, his soul twisting as new power carved itself into his very existence.

His mind expanded.

A flood of new knowledge, of new abilities, of power so immense it made his past self feel like an insect. He could feel the essence of reality itself bend to his will, the very laws of magic whispering their secrets to him.

His aura shifted—no, transformed.

From a powerful but contained darkness, it became something monstrous, abyssal, something that made even the most powerful Archdemons nearby instinctively lower their heads.

Then, it settled.

The flames died down, revealing Diablo.

His appearance had barely changed, yet there was an undeniable difference. His presence was heavier, more terrifyingly refined. He stretched out his hand, watching as black flames licked at his fingers, bending to his every whim.

He grinned.

"This power… is magnificent." His voice, now smoother, carried an edge of undeniable supremacy. He turned to Arion and bowed slightly, a gesture he had never given anyone before. "I am honored and swear my utmost loyalty to you lord Arion."

Arion's gaze shifted to Blanc.

"From this day forward, you shall be called Testarossa."

Just like Diablo, the moment the name left Arion's lips, reality itself trembled.

A wave of pure, searing white energy erupted from within her, blasting outward in a pulse of absolute destruction. The air itself ignited around her, turning into a swirling inferno of ethereal silver flames.

Her entire existence shifted.

She felt something deeper than mere power.

A connection to the abyss, to the unknown, to the very essence of annihilation itself. She clenched her fists, and instantly, the space around her distorted, turning into raw, unstable energy.

Her eyes glowed with an eerie silver light, her aura now exuding an elegance so dangerous it felt like a whisper of death itself.

She exhaled, and the ground beneath her froze over—not with ice, but with sheer, oppressive dominance.

She smirked, eyes flashing.

"Fascinating." Her voice carried layers of hidden menace, yet it was also undeniably seductive, alluring in its lethality. She turned to Arion, placing a hand over her chest as she bowed gracefully.

"You have my loyalty, my liege."

One by one, Arion named every single Archdemon.

With each name, a new explosion of power shook the forest, warping the very space around them.

Each Archdemon was already a force to be reckoned with, but now, they transcended. Their bodies, once solid and defined, became something greater—something ethereal yet devastatingly real.

Their horns grew longer, their aura thickened with abyssal grandeur, and their eyes gleamed with newfound intelligence and cruelty. Their very presence now demanded submission.

They were no longer just Archdemons.

They were Demon Nobles.

A new class of beings that stood on the very precipice of true Demon Lordhood, a status unmatched in the history of the Underworld.

—---

Then came the Greater Demons.

With every name Arion uttered, a storm of darkness erupted around them.

They screamed as their bodies reformed, twisted, and refined into something stronger, something more complete. Their once unstable and chaotic power was now sharpened, controlled, and amplified beyond recognition.

They became Archdemons.

Their once-wild energy was now precise, their killing intent sharper, their intelligence heightened. Their bodies radiated pure abyssal dominance, making even their former comrades tremble in their presence.

Finally, the Lesser Demons.

For them, evolution was nothing short of cataclysmic.

Their forms swelled with power, their bodies cracking and reforming under the pressure of their newfound strength. Some collapsed to their knees, gasping as they felt their very essence reshape itself.

They had been mere fodder before.

Now, they were Greater Demons—entities capable of crushing their former selves with a mere thought.

For the first time in their existence, they felt worthy.

When it was over, silence fell upon the battlefield.

The entire army stood transformed.

Over a thousand demons, now something far beyond what they once were.

The once-murmuring ranks were now reverent, awestruck, and overwhelmed by the sheer power coursing through them. Their eyes burned with newfound purpose, their bodies thrummed with dark might.

The newly ascended Demon Nobles bowed deeply, their voices carrying a collective, unshakable conviction.

"We are yours to command, Lord Arion."

Arion stood above them all, his expression unreadable.

But in his eyes, satisfaction burned like an unholy flame.

The Eminence of Shadow had just gained an army unlike any other.