Strongest Existence Becomes Teacher-Chapter 245: The Chrono Cube

"What if you had fifteen days?"

For a moment, no one moved.

"...What?"

All three of them reacted at once, their expressions filled with confusion.

Selene frowned, trying to make sense of it. "Professor... how is that even possible?"

Maera crossed her arms, clearly unconvinced. "Don’t joke at a time like this..."

Only Drevin remained quiet, his eyes fixed on Zane, carefully observing him as if trying to understand what he was about to reveal.

Zane, however, didn’t seem bothered by their reactions at all.

"I’m not joking," he said simply.

Then he reached into his dimensional storage and pulled something out, placing it calmly on his palm.

A small silver cube. 𝑓𝘳𝑒𝑒𝓌𝘦𝘣𝘯ℴ𝑣𝘦𝑙.𝘤𝑜𝑚

It was smooth and metallic, but thin red lines ran across its surface in strange patterns, faintly glowing as if something inside it was alive. The more one looked at it, the more unsettling it felt—like it didn’t quite belong to this world.

Zane glanced at it briefly.

"This is it."

Maera instinctively stepped forward. "What is this...?"

Her hand began to reach toward it—

"Stop."

Selene immediately grabbed her wrist and pulled it back.

"Don’t touch it."

Maera blinked, surprised by the sudden reaction.

Selene’s gaze remained locked on the cube, her expression tense and cautious. "It feels... strange. Too complex. Like something about it isn’t right..."

Zane nodded slightly, almost approvingly.

"You’re right. For your current level, it’s better if you don’t touch it."

Maera quickly withdrew her hand completely.

Selene then looked back at him, still unsettled. "Then what is it, Professor?"

Zane lifted the cube slightly, letting its faint red glow reflect in his eyes.

"This is the Chrono Cube."

A brief pause followed.

"It’s an artifact that has control over time."

Selene’s eyes widened instantly. "...Time?"

Her voice dropped, disbelief clear in it. "That’s impossible..."

Zane gave a small, amused smile and shook his head.

"You don’t get to decide what’s possible and what isn’t."

Then, without making it sound grand at all, he continued explaining.

"Inside this cube, time flows much faster than outside. One hour here equals one full day inside."

The meaning of his words sank in slowly.

Maera’s expression stiffened.

Selene went completely silent.

Even Drevin’s usually calm gaze shifted slightly, the disbelief finally showing.

An artifact like this... wasn’t just rare—it was something beyond anything they had ever imagined.

Zane looked at all three of them, his tone turning slightly more serious now.

"You’ll enter this with me. And for those fifteen days..."

His eyes sharpened.

"You’ll train with everything you have."

The cube continued to glow faintly in his hand, its presence alone enough to make the air feel heavier.

For a few seconds, no one spoke.

Then Zane gave a small smile, completely at ease—as if none of this was extraordinary to him.

"So," he said casually, "shall we go?"

"So... shall we go?"

Before any of them could even respond—

The cube in Zane’s palm shifted.

A faint mechanical hum echoed as the top split into four perfect squares, unfolding outward like petals. What lay inside wasn’t machinery... not even space.

It was just—

Whiteness.

Endless, depthless white.

And then—

A pull.

Before Maera, Selene, or Drevin could react, their bodies were dragged forward and swallowed into the cube.

The world twisted for a fraction of a second.

Outside—

Zane remained standing alone.

The cube rose from his palm, floating gently in the air as if weightless.

He looked at it calmly.

"Let’s go."

And the next moment—

He too was pulled in.

The cube snapped shut.

Then—

It vanished.

---

Silence.

A few seconds later, the three of them opened their eyes.

They found themselves standing in a room.

Not what they expected.

A simple interior—clean, quiet. To one side was a kitchen area, fully arranged with utensils and supplies. On the other side, two doors led to separate rooms. In front of them stood another door, larger than the rest.

Selene blinked.

Maera looked around slowly.

Drevin frowned slightly.

"...Where are we?" he asked.

Before anyone else could answer—

Zane appeared in front of them.

He looked completely normal, as if nothing unusual had just happened.

"What, you all are this slow?" he said casually. "Come on."

Without waiting, he walked forward and opened the door ahead.

"Welcome," he said, "to the inner world of the Chrono Cube."

They stepped forward—

And froze.

Beyond the door wasn’t a room.

It was an entire world.

A vast open grassland stretched endlessly in all directions. The sky above was a clear blue, untouched by clouds, and a white sun hung calmly in the distance, casting soft light over everything. There were no buildings, no creatures, no signs of life.

Just empty, endless land.

All three of them stood there in silence, their eyes wide as they took in the sheer scale of it.

Maera was the first to speak, her voice carrying a strange mix of awe and discomfort.

"...A blue sky... and a white sun..."

She let out a small breath.

"It still feels weird seeing this..."

Zane glanced at her briefly, then back at the open world.

"This is where you’ll train."

He turned slightly and gestured behind them.

"That space back there has everything you need. A kitchen for basic food, rooms for rest, and all essential facilities."

Then he added—

"And one more thing."

"There’s a rejuvenating pond."

His tone remained casual, but his words weren’t.

"If you soak in it, it can heal physical injuries and remove fatigue completely."

That—

That made them freeze again.

Selene’s eyes widened.

Maera looked stunned.

Even Drevin’s calm expression cracked.

An environment where time flows faster...

A space like this...

And something that could completely restore the body...

They had expected something extraordinary.

But this—

This was beyond that.

Zane looked at them, a faint smirk forming on his face.

"Alright," he said.

"Let’s get started."

.

.

.

The vast grassland stretched endlessly before them, the white sun hanging still in the sky as if time itself had paused just to watch.

"Alright," Zane said, dusting his hands lightly. "Before we begin..."

He turned slightly, glancing at the device on his wrist.

"Let me introduce you to someone who’ll assist me in training you."

The three of them looked at him, still not fully recovered from everything they had just seen.

Zane tapped his technowatch.

"Eira, come out."

At first, nothing happened.

Then—

Light.

Tiny holographic particles began to spill out from the watch, glowing faintly as they spread into the air. They gathered, swirled, and aligned themselves in precise patterns, forming outlines, then shapes... then a body.

Within seconds—

A full humanoid hologram stood before them.

Life-sized.

It was Eira.

But not the small floating version they had seen before.

Her appearance had changed.

Her stormy grey hair was now styled into a sharp bob cut, framing her face neatly, while her eyes had shifted into a hazy greyish-purple glow that gave her an almost otherworldly presence. Her outfit was completely different as well—an oversized futuristic white puffer jacket draped over her frame, its thick quilted panels embedded with glowing red circuit-like accents. Beneath it, a sleek black netrunner-style suit hugged her form, paired with white tactical shorts, high gray stockings, and reinforced black boots detailed with red lines.

She looked—

Modern.

Sharp.

And completely out of place in a medieval academy world.

Zane stared at her for a second.

"...When did you change your clothes?"

Eira crossed her arms casually.

"Boss, you changed your clothes too," she replied with a playful tone. "So I thought it makes sense for me to upgrade my look as well."

Zane narrowed his eyes slightly.

"...That explains why you were so quiet."

A pause.

"You were busy doing this."

His gaze moved up and down her outfit.

"And you even went with a futuristic theme."

Eira gave a cheeky smile.

"Gotta keep up appearances."

Then she turned toward the students, her holographic form flickering slightly as she waved.

"Anyway—hiya, kids."

Her tone brightened instantly.

"I’m Eira. Living AI, personal assistant to this guy," she jerked a thumb toward Zane, "and I’ll be helping train you."

She leaned forward slightly, hands behind her back, smiling playfully.

"So... are you happy to see me?"

The three of them just stared.

Processing.

Trying to connect memories.

And then—

Recognition hit.

Maera and Selene spoke at the same time.

"...It’s the crazy lady who followed Professor to save the world!"

Eira froze.

Her holographic face glitched for a second—

Then flattened into the most exaggerated blank expression possible.

"...Huh?"