Duke Gilberto stated that the door to the Vault was right here in this room.
If the inner palace served as the royal family's residential quarters, it certainly made sense.
"The location is—"
"Wait just a moment."
Jin stopped the Duke.
"Is it really all right to let an outsider hear such a thing?"
"Yes."
The Duke nodded with a serious expression.
"You may be an outsider, Jin-dono, but you don't belong to any specific nation, do you?"
"Well, true enough."
That was what Jin had just said himself earlier.
"Because you are such a neutral party, Jin-dono, I want you to be present."
"...Understood."
It was proof of just how deeply the Duke trusted him.
"Now, as for the location of the door, it is right beneath this bed."
"Huh?"
"If you move this bed aside, the door will be revealed," the Duke explained. "I will call a working golem right away—"
"...No, there's no need for that. Reiko, please."
"Yes, Father."
Jin decided to have Reiko move the bed instead.
"Oh, Lady Reiko is an automata, isn't she? In that case, she must possess a decent amount of strength... Wh-Whaaat?!"
Grabbing the edge of the bed frame, Reiko effortlessly lifted it and carried it to the corner of the room. With the Duke still lying on top of it, of course.
She even subtly deployed a barrier projector, taking great care to ensure the bed suffered no structural strain.
Unaware of that fact, the Duke and Nanaria stared in stunned disbelief, their eyes wide with shock.
Once they pulled back the rug covering the floor where the bed had been, a trapdoor was indeed revealed.
"First, please use this to unlock it."
The Duke handed Jin a silver-colored key.
When Jin inserted it into the floor lock and turned it, the mechanism disengaged with a heavy clunk.
The door in the floor was designed to be lifted open like double doors.
Beyond it lay a stone staircase leading down into the dark.
"If you descend about thirty steps, you will reach another door. That door uses this key."
The Duke held out the gold key, but Jin did not take it.
"No, please use it yourself."
"However, I still cannot walk properly..."
Because he had been bedridden for so long and had suffered from symptoms of beriberi, the muscles in his legs had not yet recovered.
"Therefore, please go with Nanaria."
"...Understood."
With the Duke insisting to that extent, Jin could hardly refuse.
"I shall take the lead."
Reiko took the front, leading the way down the steps. The staircase was about a meter wide. With the light spilling from the bedchamber above, their footing was clearly visible.
The keyhole on the door at the bottom of the stairs could also be faintly made out.
Reiko stepped aside for Nanaria.
"Please open it, Lady Nanaria, as His Grace's proxy."
Holding the key, Nanaria took a step forward.
"...W-Well then, I shall open it."
Nanaria inserted the gold key into the keyhole and turned it.
With a light click, the lock opened.
From there, Reiko took the lead once again and pushed the door inward.
Beyond the door, which swung open with a faint creak, lay a fairly spacious room.
Ether Lights were mounted on the ceiling, automatically illuminating the chamber.
(...?)
The subtle familiarity Jin had felt ever since walking down the stairs grew even stronger.
No, rather than "familiarity," it would be more accurate to call it a sensation that everything felt entirely natural.
In short:
(This place... Could it have been made by me in the past, or by someone related to me?)
That was the conclusion he arrived at.
However, since this palace was estimated to have been built around 150 years ago, it could not have been made by the Jin of the past.
In that case, it was only natural to assume it had been constructed by someone connected to him.
(...It's probably Quinta.)
Back before Hourai Island had ever been subjected to attacks by Markitus and the Magic Federation, Laojun had dispatched Quinta units across the world to gather intelligence. Jin deduced that one of those units must have operated in this country as an engineer.
With that mystery settled in his mind, Jin took another look around the room.
Almost the entire ceiling was fitted with Ether Lights. Since the luminous intensity per unit area was kept low, looking up at them did not strain the eyes.
(Maybe to cut costs?)
Generally speaking, brighter Ether Lights were far more expensive. Considering cost-effectiveness, using numerous dimmer lights ultimately proved much cheaper.
Jin rarely factored costs into his own crafting, but he knew at least that much as common sense... barely, anyway.
The walls were built of stone treated with Toughening, matching the material used in the Royal Palace. The floor was crafted identically.
And above all else, there was a single golem mounted to a built-in hanger on the far wall.
Since it stood directly opposite the entrance, it caught one's attention the instant they stepped into the room.
In fact, Nanaria seemed completely captivated by it.
It was a male-type standing roughly 1.8 meters tall, which placed it on the somewhat smaller side for a golem.
Its finish was a deep blue. The exterior armor was likely 64 light silver (= titanium), with its color produced through controlled surface oxidation.
It possessed a clean, functional outline devoid of superfluous spikes or decorations—a minimalist aesthetic that strongly echoed Jin's own design lineage.
"May I take a closer look?" Jin asked.
Nanaria snapped back to her senses.
"Ah, yes! Please, go right ahead, Jin-sama."
With that, she stepped aside.
"Excuse me, then."
When Jin examined the golem with Analyze, a wealth of technical details became clear.
It was, as expected, an Adriana-style Golem.
Its exterior plating was 64 light silver. The internal frame was identical. This specific alloy composition was unique to Hourai Island.
Looking at the overall internal architecture, it was virtually identical to Land.
In other words, it was undeniably of Hourai Island origin... or more accurately, a creation directly derived from Jin's lineage.
The craftsman was, just as he had suspected, a member of Quinta: Regulus 48, commonly known as Galias.
Its date of manufacture was recorded as the year 3761.
Its overall performance was roughly one-third that of Land. Even so, it had been the pinnacle of golem craftsmanship in that era outside of Hourai Island, and it remained so even today.
When Jin summarized the findings for Nanaria, omitting any references to Hourai Island, her reaction was immediate.
"That is incredible! The Blau Ritter! It really did exist!"
She rejoiced, practically beaming with delight.
According to her, an oral tradition stating that the legendary Blau Ritter was secretly preserved within the vault had been handed down through generations of the ducal family.
As for why Nanaria—who was not yet the duchess consort—knew about it, she, too, carried the bloodline of the ducal family through a collateral branch.
"Will it still move?" Nanaria asked, her violet eyes sparkling with anticipation.
Reasoning that there was no need to hide anything from someone tied to the ducal family, Jin offered a straightforward reply.
"Of course it will."
Jin shared that truth with her without hesitation.