The proposal to prepare magi-devices for Ventilation or Dust Collection in the mines was relayed to Avalon through Laojun.
"Lord Tomax, I looked into the records, and it turns out there was a time prior to the rise of the Magic Federation when workers in the mines—particularly in the deep sections—were replaced by golems. That was roughly two hundred and fifty years ago."
The secretary automaton Manon delivered her report.
"Mmh, then it's no wonder the present conditions are so terrible."
Even Tomax found the historical tragedy easy to comprehend.
"And so, Deus Ex Machina-dono will be supporting this initiative as well, I presume?"
"Yes. More precisely, Jin-dono as well."
"I see. Having both of them on board is worth the strength of a thousand men."
Ever since Manon's arrival, Tomax Bertman's workload had plummeted to less than a third of what it had once been. Not only did he now get adequate sleep, but his overall health had improved, allowing him to take on new projects without a hitch. Even his chronic stomach pains had cleared up. With Simone, an automaton identical in model to Manon, joining the team, he was able to fulfill his duties as Chief Administrator to the utmost.
"Ten prototype units of a magi-device called an 'Air Purifier' are scheduled to arrive tomorrow. Since they are test models, their request was for us to try them out first and report back on anything we notice."
"Indeed, that makes sense. In that case, let us lend one unit each for testing to the Klein Kingdom, the Kingdom of Franz, the Kingdom of Egerea, the Kingdom of Elias, the Celuroa Kingdom, the Shouro Empire, and the autonomous district in the former Leonard Kingdom."
"Shall we keep the remaining three units as spares?"
"That would be best."
In reality, the Air Purifier magi-device crafted by Jin posed no particular issues.
Laojun possessed operational data from historical models, which Jin had used as a reference point.
As a result, crafting them had gone without a hitch.
If any improvements were to be suggested, they would likely pertain to cleanup capacity—simply a matter of scale.
It would likely take several more days for the test results to come in.
Having wrapped up their necessary meetings, Jin and Elsa had returned to Hourai Island.
The date was January 10, 3901.
"Since the construction work over there has been left to the local contractors, next up is the Shouro Empire."
"We've been busy."
"Yeah. But at least we won't get bored....Let's go together this time."
"Mm."
Jin also intended to introduce Elsa as Elsa sooner rather than later.
In the Klein Kingdom, they had introduced her as Erna. Since that rumor had likely spread, Jin wanted to set the record straight as soon as possible.
"Well, the first day will probably wrap up with just meetings. The construction will start around the third day, I imagine."
Jin was considering deploying Daidara this time to level the ground.
"Should we say we flew over in Condor and that it took two days to get there?"
"My Lord, if we do that, may I take it that you intend to formally reveal Condor and Daidara to the public eye?"
"Yeah... though Daidara aside, revealing Condor might be problematic, don't you think?"
While Jin wished to showcase considerably advanced technology soon to inspire other craftsmen, he felt that making such a massive leap forward while the Blow Floater was still in its developmental infancy might cause unnecessary friction.
"Then Daidara is fine, but why don't we build a large-class Blow Floater capable of transporting it?"
"That might be good."
Elsa agreed, anticipating that there would be many occasions to transport heavy machinery and large quantities of supplies in the future.
"Daidara weighs about eight tons. So we'll need to make something capable of hauling around ten."
While Jin wasn't an expert on military hardware, he knew that the Self-Defense Forces' CH-47—a tandem-rotor helicopter—was said to have a payload of roughly eight tons.
Aerodynamically speaking, it was well within the realm of possibility.
Even so, the craft was bound to be massive.
"Just like Condor, let's give it four circular wings for levitation, arranged at the corners of a square."
"The diameter of the circular wings will likely need to be around fifteen meters."
With Laojun's technical input, the dimensions were settled.
"That's pretty big....Let's install a force generator as well to minimize the risk of a crash."
Step by step, the primary specifications took shape.
"Let's use 64 light silver to keep it light and sturdy."
For the cables used to suspend Daidara, they decided on magi-type reinforced materials capable of holding up an eight-ton load.
As for the manufacturing site, Jin considered the airfield behind the laboratory.
Since there was no hangar capable of housing an aircraft of this scale, they resolved to build one concurrently—essentially a combined dry dock and hangar.
However, Jin paused to think it through carefully.
"Still, I really don't want to clear out too much land around the laboratory..."
Building something on the scale of the Mansion or a hokora was fine, but he hesitated at the thought of large-scale development spanning several hundred meters.
Hearing Jin's murmur, Elsa chimed in with an intriguing idea.
"Then why not build it underground?"
"Eh?"
"A lot of our past opponents had underground bases, so I thought Jin-nii could just do the same."
Evidently, she held no particular obsession with underground bases; it was merely a conclusion reached through practical deduction.
"That makes sense."
Presently, Hourai Island possessed no aircraft requiring a long runway.
Since earlier models like Albatross, Skylark, and Pelican were all fitted with force generators, every last one of them operated as a VTOL craft.
"In that case, if we install a hatch about fifty meters across, it should work...?"
Having grown up admiring the secret bases of tokusatsu shows and anime, Jin was thoroughly enthused by the concept.
Naturally, finishing everything in a single day was out of the question.
"Hmm, what should we do?"
There were three options:
Postpone the trip to the Shouro Empire (though only by about three days).
Have Laojun carry on with the construction while Jin and the others went to the Shouro Empire (since they wouldn't need Daidara immediately).
For the time being, send a Doppel to the Shouro Empire instead (with Laojun handling most of the piloting).
"Well, option one should be fine."
They hadn't yet sent word or finalized their itinerary for the Shouro Empire.
Jin had initially considered the 11th, but purely because of the pleasing alignment of three ones.
"Let's set our departure for the Shouro Empire on January 15th, and focus entirely on the construction here for now."
Jin gave the order.
"Understood, My Lord."
First came the development of the underground level.
The ground around the laboratory was solid and durable, making it ideal for an underground base.
They hollowed out a subterranean vault measuring two kilometers across and one kilometer deep. After hardening the perimeter walls with Toughening, they reinforced them further with structural steel.
Leaving the surface intact, they carved out the earth beneath.
The excavation was carried out using magi-craft alongside ten giant golem Daidara units, wrapping up in just half a day.
Because the excavated dirt was cleared away via Warp Gate, the work progressed at breakneck speed.
They built it on this scale so that it could also hangar spaceships, beginning with the flagship Adriana.
"All right, let's put a lid on it."
The surface above the excavation—or rather, the underground base—would retain the original airfield, with the natural vegetation fully restored.
That said, because the vast majority of the work had been done by tunneling below, the surface required very little effort.
By utilizing magic circles, an access hatch wasn't strictly necessary.
Even so, to satisfy Jin's personal tastes and provide an emergency route, they went ahead and built hatches anyway.
The largest hatch measured one hundred meters square, intended for large-class craft like Condor.
For emergency access, ten human-sized hatches were installed at various points.
Throughout the underground levels, Warp Gates leading up to the surface were slated for placement at key junctions.
And then...
"Sounds like you're working on something interesting."
Reinhard spoke up as he strolled over.
"Jin, let me lend a hand too!"
"Sure, I'm counting on you."
And with that, Reinhard joined in on the construction of the underground base.