After leaving the sanctuary, Rozen and his group returned to the underground space at the bottom of the cliff, which had previously been sealed off by Irori's ice, preventing any monsters from entering. Now standing once more on this cold, frost-covered land, a heavy silence hung in the air.
Rozen himself aside, Irori, Yaya, and Komurasaki were all still reeling from the encounter inside the sanctuary—with that giant monster named Androgyne. It was hard for them to believe that such a thing could exist beneath the Academy.
What exactly was that?
A Machine Doll developed by the Academy?
But Rozen clearly said it was unfinished.
Could it be a Machine Doll still under development, not yet fully formed?
What would it even take to create such a thing—how could something like that be made?
As automatons themselves, Irori, Yaya, and Komurasaki simply couldn't ignore the matter, and the weight on their hearts was clear.
Seeing the girls looking downcast, Rozen gave a bitter smile and spoke.
"Alright, don't think too much about it. Since it's already appeared, let's just go with the flow."
Rozen offered some mild encouragement.
The girls looked at Rozen one by one, and soon their attention was drawn to the bluish gemstone in Rozen's hand.
"What is that stone, Rozen?" Komurasaki asked brightly, perhaps trying to change the subject and lighten the mood.
"This?" Rozen held up the stone with a smile and said, "Didn't I just say? It's called a Keystone."
"Keystone..."
Yaya muttered the name.
"Could it be the stake left by Yatsukamizu no Mikoto?"
Irori asked as if recalling something.
The "Yatsukamizu no Mikoto" she mentioned is a mighty deity from Japanese mythology, said to be a god of civil engineering and land. He could cast a great net into the sea and draw in islands, and when he walked across the land of Japan, his footprints became lakes. A god of immense power.
According to legend, this god once planted wooden stakes into the Japanese earth to suppress earthquakes. Over the centuries, the wood slowly petrified and turned into stones—these were the Keystones.
That's why Irori referred to it as the stake left by Yatsukamizu no Mikoto.
Of course, another version of the myth says that earthquakes were caused by a giant catfish beneath the earth. When the catfish moved, the ground shook. The god of Kashima Shrine nailed the catfish down with a stake to stop the quakes—and that stake was also known as a Keystone.
In Japanese folklore, Keystones are guardian objects against earthquakes. Kashima Shrine even enshrines one such Keystone believed to be the physical embodiment of a protective deity. In earthquake-prone regions, families often keep a stone resembling a Keystone in their homes to suppress seismic activity.
In short, the Keystone is seen by the Japanese as a divine guardian of the land.
But...
"In this context, the Keystone is explained from an engineering perspective." Rozen shook his head, denying that interpretation. "Magnus mentioned earlier that this stone goes by many names. If I'm not mistaken, the Church calls it the Original Sin Stone, historians call it the GI Crystal, and scientists call it the Stone of Nothingness. Depending on the viewer, it's a different thing—but ultimately, it's something we all know very well."
What is it?
"The most widespread magical circuit in the world—the foundation of the Machinart system itself, the source of life and soul in all automatons: the Eve's Heart."
Rozen narrowed his eyes as he looked at the gem in his hand and spoke.
"This Keystone is its prototype."
At that, Irori, Yaya, and Komurasaki all widened their eyes.
"Prototype?"
The three girls stared at the magic stone in Rozen's hand in astonishment.
Rozen gave a small smile.
"You all know, don't you? That the so-called Eve's Heart is the origin, the starting point, and the very beginning of machinart civilization?"
Rozen began to explain.
"It's a mysterious black box, full of unknowns. Many parts remain unexplained to this day. Replicating it is relatively easy, but designing it from scratch is virtually impossible. Even now, every workshop that creates automatons relies on a replication template. No one has succeeded in making one from nothing."
If that's the case, where did the original Eve's Heart come from?
In other words, where was the first mother core?
The answer was now right before their eyes.
"It's right here—before you."
Rozen held out the magic stone in front of the girls, leaving them in complete shock.
Because what they were seeing now—was the very beginning of machinart civilization. The origin of the current era.
Without it, automatons would not have life.
Without it, machinart would never have developed this far.
It was a miraculous relic capable of reproducing life. Even if its functions were different now, it was akin to the Holy Grail of this world.
You could say that all automatons originate from it.
Including Irori, Yaya, and Komurasaki.
"In the mythology of the Bible, it was preserved by the Church as the treasure left behind by the Savior. That was until a schism in the Church occurred, formally dividing it into two factions in the 11th century. Around 700 years ago, during the Fourth Crusade's infamous assault on Constantinople, the West seized it."
Rozen continued calmly.
"Even then, it remained the symbol of the Pope's and the Church's authority—until just before the Renaissance, when an atheist from Italy stole it. He extracted part of its power and created replicas. That's when the magical circuit known as the Eve's Heart was born."
After that, this human treasure likely changed hands many times before falling into the possession of the man considered the strongest magus of the 19th century.
"Upon obtaining this relic, Edward Rutherford's desire for Machine Dolls flared to life."
Rozen looked to the girls.
"You all should know the basic method for constructing an automaton, right?"
At that, Yaya quickly raised her hand.
"Yaya knows!" she exclaimed. "First, you have to create a physical body as the hardware, and then install a magical circuit as the software. Only by combining the two can a proper automaton be born!"
This had been discussed before.
Automatons consist of hardware—the body—and software—the magical circuit. The combination of both is what gives rise to a proper automaton.
Puppeteers have always focused their research on these two areas: building powerful rigid bodies for the automaton's physical frame, and designing diverse magical circuits to enhance their magical abilities.
Now here comes the question.
"Machine Dolls are, in the end, still automatons."
Rozen stated.
"So to create one, you'd still need both components, wouldn't you?"
That's exactly it.