The Greatest Assassin Gets Reincarnated in Tensura

Deep within the Jura Forest, in a hidden cavern surrounded by thick vegetation and untouched wilderness, two figures stood in silence. Arion, his golden eyes calm and calculating, gazed at the mighty Storm Dragon, Veldora. The air between them crackled with power.

Veldora stretched, cracking his knuckles, his golden lightning flickering around his body. "So, what's the plan? Are we going to start building this secret organization of yours, or are we just going to stand around and admire the scenery?"

Arion crossed his arms, his gaze unwavering. "Before we do anything, we must first train. We have both obtained new powers, and while they may feel natural, mastering them is an entirely different matter."

Veldora grinned. "Hah! That's what I like to hear! Ever since I got my new Ultimate Skill, Faust, Lord of Investigation, I've been itching to test it out."

Arion simply nodded. He did not mention his own new abilities.

Veldora tilted his head. "What about you? You must have gained something crazy too, right?"

Arion's expression remained neutral. "You'll find out soon enough."

Veldora let out a short chuckle. "Heh, keeping secrets now? Fine by me! That just makes it more exciting." He clenched his fists, his energy flaring. "So where are we doing this?"

Arion raised a hand. "We will train in my special dimension. There, we can fight without limits."

The moment he finished speaking, his voice rang within his mind. "Lara, prepare the training dimension."

From deep within his consciousness, his ever-loyal artificial intelligence, Lara, responded.

"Acknowledged, Master. Time dilation set: One day in the real world will be equivalent to ten years inside."

Arion turned back to Veldora. "Are you ready?"

Veldora smirked. "More than ready."

In an instant, they vanished.

They arrived in a realm of endless darkness—an abyss that stretched infinitely in all directions. Unlike the mortal world, there was no land, no sky—only a vast, empty void pulsing with raw magicules. This was a world without limits, where time and space bent to Arion's will.

Veldora took a deep breath, rolling his shoulders. "Hah… this place feels weird. But I like it." He flexed his fingers, golden circuits appearing around his body as Faust activated. "Alright, let's get started,"he said, rolling his shoulders, his eyes glowing with anticipation.

Arion simply nodded. He spoke no words—but his golden gaze burned with the same fire.

Then—they vanished.

The first clash shattered the abyss.

Veldora struck first—his body becoming a living storm as he exploded forward. His fist, wreathed in golden lightning, rocketed toward Arion like a comet.

Arion blinked out of existence.

Veldora's punch tore through the void, ripping apart the very fabric of the dimension. A gaping black chasm formed, its edges crackling with unstable energy. But before he could adjust—

Arion materialized behind him.

His fist, cloaked in abyssal power, buried itself into Veldora's spine.

BOOM!

Veldora shot forward like a meteor, crashing through a series of floating landmasses that shattered upon impact.

But before the dust could settle—Veldora reappeared.

His wounds were already gone, sealed by his limitless regeneration. He grinned.

"Fast, but not fast enough!"

He raised a hand—thousands of golden lances materialized instantly.

Arion's eyes narrowed. He vanished again.

The spears shot forward at impossible speeds, warping space with their sheer force. But Arion wasn't just dodging—he was dancing through dimensions, slipping between reality and non-existence.

Veldora growled. His golden circuits flared.

"Enough of this—Dragon's Judgment!"

The abyss itself trembled as divine lightning exploded in all directions, creating a storm so vast it threatened to consume everything.

Arion's smirk deepened. He raised a hand.

And the lightning was swallowed whole.

Veldora's eyes widened. "What?"

The void bent to Arion's will, absorbing the attack and dispersing it into nothingness.

This was only the beginning.

By the third year, the battlefield had completely transformed.

Veldora had become faster, stronger, and infinitely more precise. His Faust, Lord of Investigation now allowed him to predict Arion's movements before they happened. Every attack was pre-calculated, every counter perfectly executed.

But Arion was evolving too.

And he wasn't alone.

Within Arion's mind, Pandoria, the sentient core of his power, had been working tirelessly.

"Your skills… they are powerful, but fragmented. Let me refine them for you."

As Arion fought, she merged his abilities, crafting something far greater than before.

Void Stride and Dimensional Traverse were fused into:

➤ Abyssal Horizon: Lord of Infinite Pathways – The power to not only teleport but to exist in multiple dimensions simultaneously, allowing Arion to attack from countless angles at once. He could phase through reality itself, bypassing all barriers, even conceptual ones.

Ultra-Speed Regeneration and Null Presence were fused into:

➤ Abyssal Phantom: Lord of Endless Rebirth – A state where Arion could heal faster than even conceptual erasure. His presence became impossible to detect, as if he never existed. Even time itself failed to register him.

Finally, his two Ultimate Skills—Monarch of the Void and Abyssal Dominion—were merged into something beyond comprehension:

➤ Pandemonium Abyss: The Infinite Shadow Emperor – With this, Arion did not control the void—he became it.

He was the abyss itself, an entity that could no longer be bound by reality, a presence that existed outside fate.

The moment his power settled, Veldora froze.

He had sensed everything.

Arion slowly lifted his gaze, his golden eyes now holding the abyss itself.

Veldora's grin widened. "Now this… this is interesting!"

The battle changed.

Where before, Arion had been dodging, now he was everywhere.

A thousand afterimages—no, not afterimages. They were all real.

Veldora lashed out, his golden lightning obliterating everything in its path. But every time he struck an Arion, another appeared behind him, beside him, above him.

Abyssal Horizon was unstoppable.

Veldora snarled, his circuits flaring. "Fine. Then let's see you dodge this!"

His hands came together—the entire abyss was swallowed by a golden storm.

"Dragon God's Wrath!"

A planetary explosion erupted, erasing the battlefield, consuming everything in a blinding surge of destruction.

For a moment, all was still.

Then—

A whisper.

"I was never here."

Veldora's instincts screamed. He turned just in time to see a black blade pierce his chest.

Arion stood there, unmoved, his presence like a shadow that had always existed.

Veldora coughed. Then, he laughed.

By now, they were no longer just fighters.

They were monsters among monsters.

Their clashes ripped through time, their attacks no longer even resembling conventional combat.

Veldora had reached a point where his thoughts alone could manipulate reality.

His golden lightning became absolute—it no longer needed to strike. It simply declared its target destroyed.

And Arion?

He was untouchable.

He had transcended mere movement—he could now erase himself from the concept of existence, making him immune to attacks even before they were launched.

They fought endlessly, neither gaining the upper hand.

Then, something changed.

For the first time, they stopped.

Their bodies were bloodied, broken, but neither showed pain. They were equals.

Veldora grinned, stepping forward and slamming a fist against Arion's chest. "That… was the best fight of my life."

Arion smirked. "It's not over. Next time, I'll still win."

Veldora chuckled. "You wish."

With that, the void shattered.

They returned to the real world—ten years stronger.

And now… it was time for their true mission to begin.