The Greatest Assassin Gets Reincarnated in Tensura

Testarossa stood before the towering, twisted fortress that marked Violet's domain in the Underworld. The structure was a cathedral of suffering, its obsidian walls slick with blood and pulsating with violet flames that devoured the air itself. The ground was a writhing mass of tormented souls, their screams merging into a symphony of agony. Violet had turned this place into a monument of terror, a realm where pain was worshipped and despair was eternal.

The moment Testarossa arrived, the guards—mutilated horrors stitched together from countless victims—immediately surrounded her, weapons raised. Their hollow eyes burned with madness as they snarled, their voices layered with the tormented echoes of the souls trapped within them.

"State your purpose, intruder!" one of them barked, his voice like grinding bones.

Testarossa didn't even spare them a glance. "Summon Violet. Tell her the White Primordial has come to speak."

The guards hesitated. One of them, a beast with rotting wings and jagged fangs, scoffed. "You think the Mistress will—"

Testarossa flicked her wrist. A crimson arc of power sliced through the air, and the guard's head rolled onto the ground, his body collapsing in a heap before the others could even react. The remaining demons trembled as Testarossa's red eyes glowed with cold amusement.

"Go," she said, her voice calm yet carrying the weight of death itself.

The guards scrambled inside, leaving the headless corpse behind.

The throne chamber was a den of carnage. The walls were adorned with the flayed bodies of demons, still twitching, their suffering never-ending. Tortured souls hung from the ceiling on hooks, their blood forming intricate runes on the black stone floor. Violet sat lazily on her throne, her violet hair cascading over her shoulders, her fingers lazily twirling a bloody dagger as she carved into the flesh of a still-living demon sprawled at her feet.

She barely looked up as Testarossa entered. "Well, well. The great White Primordial graces me with her presence after all these years." Her lips curled into a wicked grin. "Looking to be tortured?"

Testarossa waved a hand dismissively. "As delightful as that sounds, I have come with a different purpose." Her red eyes gleamed. "I am no longer simply the White Primordial. I have taken a name—Testarossa."

Violet raised an eyebrow. "Oh? That's why you feel different." She smirked. "But tell me, Testarossa, why are you here? Certainly not just to show off your fancy new name."

Testarossa's smirk vanished. "I have come to recruit you for my lord, Arion."

Violet blinked, then burst into laughter. "You? Bowing to someone else? And you expect me to do the same?" She leaned forward, her violet eyes gleaming with amusement. "You really have gone soft."

Testarossa's aura flared dangerously, the temperature in the room dropping as the tortured souls around them wailed in terror. "I do not bow. I align myself with power."

Violet smirked. "Oh? And what if I say no?"

The air grew heavy as Testarossa's crimson aura exploded outward. The entire throne room trembled, cracks forming along the obsidian walls. The tortured souls shrieked in agony as the sheer force of her presence shattered their bindings, obliterating them instantly. Violet's throne itself groaned under the pressure, the black stone beginning to crack.

Violet's smirk faltered for just a moment before she grinned. "So, you want to fight?"

She stood, stretching her limbs, her own violet aura flaring to life. The room darkened as shadows twisted and contorted around her. "Fine. Let's see if you've still got it, White."

Violet blurred forward, her claws slicing through the air at lightning speed. Testarossa dodged effortlessly, her movements precise and elegant. With a flick of her wrist, she summoned a crimson blade and slashed, forcing Violet to leap back. The impact of Testarossa's strike split the ground, sending shockwaves through the entire castle.

Violet laughed, her eyes burning with excitement. "You always were fast, but let's see how you handle this!"

She vanished, reappearing behind Testarossa with a barrage of deadly strikes, each one aiming to tear through her flesh. But Testarossa was faster. With a graceful step, she evaded every attack, countering with a brutal kick that sent Violet crashing through the wall.

Dust and debris rained down as Violet emerged, licking the blood from her lips. "Alright, now this is getting fun." She spread her arms, summoning massive tendrils of violet energy that lashed out like whips, tearing through the very fabric of the room.

Testarossa raised a single finger.

In an instant, an overwhelming force crushed down on Violet. The tendrils disintegrated. The entire castle groaned as the sheer weight of Testarossa's power became unbearable. The remaining walls shattered, the ceiling collapsing as the entire fortress began to implode.

Violet gasped, dropping to one knee as the crushing force pressed down on her. Blood trickled from the corners of her mouth. "You… damn…"

Testarossa stepped forward, her heels clicking against the shattered stone. She grabbed Violet by the throat and lifted her effortlessly, her red eyes glowing with authority. "You are strong, Violet. But I am stronger."

Violet growled, struggling, but Testarossa's grip was unyielding.

Testarossa leaned in, her voice like silk wrapped in steel. "Submit, or be erased."

Violet grit her teeth, glaring at Testarossa with defiance… but the truth was clear. She had lost.

With a heavy sigh, she finally smirked. "Tch. Fine. You win, Testarossa. I'll go with you. But if this Arion of yours disappoints me, I'll kill him myself."

Testarossa released her grip, letting Violet drop to the ground. "You won't be disappointed." She turned, walking toward the ruined entrance. "Now, get up. We have a new future to claim."

Violet wiped the blood from her lips and chuckled. "Heh. This might actually be interesting."

With that, the two Primordials vanished into the darkness, leaving Violet's ruined castle behind—proof of the overwhelming power that had just been decided.

----____--

The moment Diablo, Testarossa, Violet, and Jaune stepped through the void, they arrived at the heart of the City of Eternal Nights, hidden deep within the Jura Forest.

Violet and Jaune froze. Their eyes widened in sheer awe.

The city was unlike anything they had ever seen—even as ancient Primordials who had witnessed empires rise and fall. It was alive, shifting and pulsing with an eerie, intelligent design. Black spires twisted toward the sky, their surfaces shimmering with arcane runes. Bridges of flowing obsidian extended and retracted as if responding to an unseen will.

Buildings stood in impossible angles, constantly rearranging themselves, yet never losing their structural harmony. The streets glowed with rivers of raw magicules, forming intricate patterns that pulsed with power, feeding the entire city with limitless energy.

The sky above was an endless void, not of darkness, but of swirling cosmic energy—nebulae and stars that defied reality, making it feel as though they were walking in a realm beyond existence itself. The air was thick with demonic energy, making even the strongest demons shiver under the sheer weight of its density.

Thousands of demons roamed the city, their power levels unfathomable. Some were noble aristocrats, wearing elegant, flowing robes embedded with celestial jewels. Others were battle-hardened warriors, their armor forged from metals unknown to the world, radiating an aura of absolute destruction.

Jaune and Violet exchanged glances.

"What the hell is this place…?" Jaune muttered under his breath, unable to mask his amazement.

Violet smirked but her usual arrogance was replaced by something else—intrigue. "This… is not what I expected. It's not just a city… it's a kingdom built by something far beyond a mere demon lord."

Diablo chuckled. "Impressive, isn't it? This is the seat of Lord Arion's power, a domain that rivals the heavens themselves. A city that constantly evolves, adapting, growing, thriving. It is the heart of the inevitable conquest that is to come."

Testarossa nodded. "And you, dear Violet and Jaune, are about to become a part of it."

Violet crossed her arms. "We'll see about that."

Jaune simply smirked. "Tch. Let's see what your so-called Lord is about first."

The Watchtower was the core of the city, standing impossibly tall, reaching into the endless cosmic sky. The walls pulsed with living darkness, the floor beneath them constantly shifting, as if reality itself was bending to Arion's will.

Violet and Jaune walked through the colossal doors, feeling the air thicken with an indescribable pressure. It was as if the very fabric of existence bowed to the presence within.

At the center of the grand chamber, two figures stood—one they recognized, and one they did not.

Veldora, the Storm Dragon, leaned against a dark crystalline throne, his golden eyes flickering with amusement. He exuded the chaotic energy of an untamed force of nature, a being that could reduce nations to dust with a mere flick of his wrist.

But it was the other figure that made their instincts scream.

Arion.

He stood tall, his presence majestic yet terrifying. His form radiated an unnatural divinity, yet his aura was unmistakably demonic in nature. His long, flowing silver hair shimmered under the cosmic light, and his eyes—gold and filled with something beyond mortality—pierced through them like a force beyond comprehension. His very existence felt like a paradox, as if he was both the beginning and the end.

The air itself obeyed him.

Violet and Jaune stiffened. They had fought gods, kings, and Primordials, but they had never felt this kind of pressure before.

Then, something even more shocking—Diablo and Testarossa knelt before Arion without hesitation.

"My Lord, we have returned." Diablo's voice was smooth, but beneath it was a reverence that was almost unnatural.

Testarossa followed suit, lowering her head. "As promised, I have brought them."

Violet and Jaune hesitated.

They had never bowed to anyone.

Ever.

Yet, when they felt Arion's gaze on them, something deep within them screamed at them to kneel.

Jaune clenched his fists, but before he could resist further, Diablo shot him a look—a look that promised death and worse if he disrespected their Lord.

Violet, for once, remained silent. She had already fought Testarossa and lost. If this was the being Testarossa submitted to… what did that mean for them?

Reluctantly, they both fell to one knee.

Arion's voice was smooth, calm, yet absolute.

"Tell me… do you wish to become part of something greater?"

Violet, ever the defiant one, smirked. "Tch. I don't just follow anyone. If you want my loyalty, I need to see what you're made of first."

Jaune crossed his arms. "Yeah. If you're as strong as they say, prove it."

Veldora burst out laughing. "Ohhh, I like these two! Arion, are you gonna show them?"

Arion smirked. "Fair enough."

With a snap of his fingers, the world changed.

Suddenly, they were somewhere else.

A twisted dimension of absolute nothingness.

No ground, no sky, no time—just an endless abyss that seemed to stretch beyond reality. The air burned, their bodies screamed in agony. Their very souls felt like they were unraveling.

Violet dropped to one knee. Pain. Pain beyond anything she had ever felt. It was as if her very existence was being rewritten.

Jaune clutched his chest, his heartbeat erratic. "What… is this…?"

Arion's voice echoed, but he had not moved.

"That is what it means to stand before me."

He raised a single hand, and the pain multiplied a thousandfold.

Violet and Jaune screamed.

This wasn't an attack.

This wasn't a technique.

This was simply Arion existing.

And they couldn't even breathe.

Then, the pressure lifted. They gasped, collapsing onto the void-like floor.

Arion stepped forward, his voice calm yet absolute. "Now… do you understand?"

Violet, breathing heavily, wiped the blood from her lips and grinned. "Hah… yeah. Alright. You win."

Jaune groaned, rubbing his temples. "Tch… damn it. Fine. I'll serve. But I expect some real fun out of this."

Arion smirked. "Then rise. You are mine now."

The world snapped back to reality.

Violet and Jaune stood, still shaken, but with new understanding.

Diablo grinned. "Welcome… to the future."

Veldora laughed. "Ohh, this is gonna be good."

Arion's golden eyes locked onto Jaune.

"You," he said, his voice carrying an authority beyond mere words. "From this day forth, you shall be known as Carrera."

Jaune's entire body trembled as an indescribable power surged through her.

She gasped, feeling her very essence shift—her soul being engraved with the name. The moment the name took root, her power exploded like a supernova, her magicules refining, expanding, evolving.

It was like being reborn.

She clenched her fists, feeling her new strength flow through her veins.

"I… I feel complete," she whispered, her voice laced with awe. "This… this is unbelievable."

Arion's gaze then turned to Violet.

"And you," his voice carried an almost celestial weight, "from this day forth, you shall be known as Ultima."

The moment the name was spoken, a tidal wave of energy consumed her.

Violet—now Ultima—let out a sharp breath, her entire being vibrating with newfound power.

She could feel the name fusing into her soul, shaping her existence, making her something far greater than before.

Her aura expanded, her control over destruction magic sharpening to a terrifying degree.

She slowly opened her eyes, and for the first time, a true, wicked smile spread across her face.

"This…" Ultima whispered, shivering with excitement. "This power is absolute."

Arion watched them calmly, his expression unreadable. "Now, you are whole. Serve me well, and you will continue to ascend beyond your limits."

Carrera and Ultima both bowed their heads, fully accepting their new master.

For the first time in their existence—they felt truly complete.

And so, the City of Eternal Nights gained two new monsters.