Five days had passed.
Many things, both ordinary and extraordinary, had happened during that time.
At present, Kuro was inside the workshop located within the Mirror Dimension, together with Medea.
Medea was a beautiful woman with long blue hair, adorned with a small braid on the left side of her head. Her eyes were the same color as her hair.
She wore a dark purple dress with a black cloak draped over her shoulders.
Both of her hands emitted a soft bluish glow as they hovered over a Mystic Code resembling a modern dispenser, made entirely of Vibranium.
Magical circuits engraved across the device's surface glowed faintly as Medea adjusted the thaumaturgical structure within it.
Kuro watched Medea work for a while before speaking.
"You seem to have gotten quite accustomed to using Magecraft even outside our original world."
His gaze shifted toward the Mystic Code before them.
"And you can even work on a project like this at the same time."
He paused for a moment.
"How is your progress with the Mystic Art I taught you? The one from that book."
Medea did not answer immediately. Her hands continued moving for several seconds before she finally stopped adjusting the Mystic Code.
"Quite interesting."
Her tone was calm.
"The concept is different from the Magecraft I'm accustomed to."
She looked at her own palm.
"Normally, a magus uses Od, Mana, or whatever source of energy is available in their surroundings."
"But Eldritch Magic..."
Medea frowned slightly.
"...is more akin to establishing a connection with another dimension and borrowing energy from it."
"And?"
"The connection is real."
Her answer came without hesitation.
"I've already managed to conduct several simple experiments."
Kuro raised an eyebrow.
"That quickly?"
"I am Medea."
She replied flatly.
"If a magical system has a clear theoretical foundation, learning it isn't particularly difficult."
Medea turned her attention back to the Mystic Code.
"Even so, there is one aspect I still dislike."
"Which part?"
"The risks."
She answered briefly.
"The greater the amount of energy borrowed, the greater the possibility that something on the other side will notice your presence."
She paused for a moment.
"As a magus, I prefer systems that give me complete control rather than one that requires me to rely on something beyond my observation."
Kuro chuckled.
"That sounds just like you."
Medea merely sighed softly.
"Of course. I didn't survive this long by trusting things I don't understand."
After saying that, Medea resumed adjusting the Mystic Code before them. The process continued for several moments until she finally stopped.
Her work was complete.
Both of her hands slowly lowered. Before pulling them away completely, the index finger of her right hand touched the air around the Mystic Code.
Click.
The center of the device opened mechanically. Its metal layers shifted one after another, revealing the core chamber that had previously been hidden inside.
"I've finished adjusting it, Master," Medea said. "You only need to install the energy core. After that, this Mystic Code should operate normally."
Kuro nodded.
Without saying anything, he raised his palm.
A ripple appeared in the empty space above it, and a green crystal slowly fell into his hand.
A Rare Mana Prism.
A crystal formed through the condensation of a massive amount of mana.
It took the form of a fist-sized cube, yet a single Rare Mana Prism contained an amount of energy equivalent to five hundred thousand Od.
Kuro placed the crystal into the core chamber.
As soon as the crystal was installed, the metal layers closed on their own.
The magical circuits covering the Mystic Code's surface immediately lit up.
A few seconds later, several magical energy-based projection panels appeared around it, resembling a modern holographic interface.
Kuro touched one of the panels.
The device immediately processed the command he had given.
Mana particles began gathering above it before forming a small crystal resembling a transparent pill.
Kuro smiled faintly at the result.
"With this," he said, "the Servants can at least maintain their manifestations while I explore other realities without having to bring them along."
He let out a soft sigh.
"But this is still only a temporary solution."
Kuro picked up the crystal pill and examined it.
"One mana supplement is equivalent to five thousand Od. The core has to be replenished periodically, and the Servants also have to consume them regularly."
Medea stared at the pill for a moment.
"Five thousand Od per unit isn't bad."
"But?"
"Too wasteful for long-term use."
Her answer came without hesitation.
Medea crossed her arms.
"If your goal is to maintain multiple Servants simultaneously for months or years, the energy cost will continue increasing exponentially."
She glanced toward the Mystic Code.
"This system is viable as an emergency support measure."
"But not as a permanent foundation."
Kuro nodded slightly.
He had actually reached the same conclusion.
"I suppose so."
"I can think of two solutions."
Medea raised two fingers.
"First, increase the efficiency of mana conversion so that each Servant consumes less."
"And the second?"
"Build an energy source that doesn't depend on your own reserves."
Medea's gaze returned to the Rare Mana Prism inside the device.
"As long as this system continues consuming your reserves directly, it will eventually reach its limit."
She paused for a moment.
"Besides..."
Her tone became more serious.
"If the number of your Servants continues to increase one day, this problem will only become worse."
Kuro laughed softly.
But before their conversation could continue, a very familiar voice suddenly rang through his mind via telepathy.
"Master!"
The excitement in the voice immediately told Kuro who it belonged to.
"Let's ride the Hippogriff to M City and buy some takoyaki! I heard they're really delicious!"
Kuro's eyes widened for a moment.
Just like that?
After all the discussion about the Mystic Code, mana supplies, and various rather complicated problems?
Takoyaki?
"Master?"
Astolfo's voice came again.
"Come onnn~"
Kuro held back a small laugh.
"Yeah, yeah. Give me a moment."
"Yay!"
Astolfo's cheerful cry immediately echoed through his mind.
Kuro shook his head lightly before turning his attention back to Medea.
"I'm leaving."
Medea raised an eyebrow.
"Something happened?"
"Astolfo."
Just one word.
Yet it was enough to explain quite a lot.
Medea fell silent for several seconds.
"...I see."
Kuro chuckled softly.
"I'm off."
"Don't let him destroy anything."
"That's not a guarantee I can give."
For the first time in a while, Medea visibly sighed.
Kuro simply smiled before turning around and walking out of the workshop.
***
As soon as he exited the workshop within the Mirror Dimension, Kuro found Astolfo already waiting on the rooftop of a building, together with a prepared Hippogriff.
However, before they could depart, Yuki suddenly appeared and asked to come along.
After thinking for a moment, Kuro eventually allowed her to join them.
With Astolfo in charge of keeping an eye on her and the Hippogriff being far faster than most modern forms of transportation, the chances of anything going wrong should have been fairly low.
At least, in theory.
Not long afterward, Astolfo and Yuki departed together, leaving Kuro behind by himself.
Kuro watched them until they disappeared into the distance before letting out a soft sigh.
There had been too many things for him to think about lately.
The problems concerning the Servants.
The mana supply.
The Mystic Code.
And, most troublesome of all, his plan to build a permanent base that could one day function as his own version of Chaldea.
Thinking about everything at once made his head feel a little crowded.
Therefore, rather than joining Astolfo in searching for takoyaki, Kuro decided to return to the Mirror Dimension.
Perhaps a drink and some peace and quiet would help clear his mind.
However, the moment he stepped into the mirrored world, his ears caught the sound of soft music coming from somewhere in the distance.
The melody was gentle.
It flowed slowly between the empty buildings, their surfaces reflecting the light of the setting sun.
Kuro recognized the melody almost immediately.
Or, more precisely, he recognized who was playing it.
Following the direction of the sound, Kuro eventually arrived at the rooftop of a nearby building.
A remarkably beautiful woman wearing a black-and-blue qipao adorned with cloud patterns was sitting peacefully at the edge of the building.
Her long hair swayed gently in the breeze, while a pipa rested in her hands, played with soft and practiced movements.
"Yang Guifei..." Kuro called out to the woman. "Or... should I call you Yang? Guifei? Or Yuhuan? I'm still confused about what I should call you."
A sweet smile immediately appeared at the corner of Yang Guifei's lips. The melody from her pipa came to a stop, and she turned around to look at her Master, who was approaching her.
"Just call me Yuyu," she said softly. "Or is 'Yuyu' difficult to pronounce? I think it's much simpler than calling me 'niángzi.'"