Nothing else happened that night.
Even so, Jin had taken his own quiet precautions behind the scenes.
"Laojun, who is our Quinta stationed in the Shouro Empire?"
"Yes, My Lord. It is Regulus 7, known by the alias Gaias."
"All right. Can we have Gaias get involved in the investigation into that sabotage?"
"That will not be a problem, My Lord."
"Good. I'll leave it to you, then."
Having taken every measure available to him, Jin fell asleep with peace of mind.
Incidentally, he slept inside the Hurricane rather than in a tent.
With the air conditioning running smoothly, it was plenty comfortable.
The following day, on the nineteenth, Jin, Elsa, and the Magic Technology Minister left the Torom mine and returned to the construction site.
To be safe, Deus Ex Machina remained behind at the mine, providing reassurance.
"Well, our work has been delayed by about half a day, but..." Jin began.
"Nonsense, the ground leveling and foundation work are already finished," the Magic Technology Minister pointed out reasonably. "At this stage, you may comfortably leave the rest to us."
"Is that so?"
Jin agreed that it would indeed be best to conclude his assistance here.
"In that case, I think I'll make a trip to Mitsuho."
"To Mitsuho, you say?"
"Yes. To purchase asphalt."
Jin glanced at the landed Eagle 1 as he spoke.
"We can use it to pave the walkways within the memorial hall grounds, and I'd also like to use it for paving airfields and other projects."
Even on the abundant Hourai Island, asphalt did not occur naturally. To begin with, while Planet Ars had coal deposits, very little petroleum could be extracted. Even the coal itself was not particularly plentiful.
Consequently, standard paving relied on macadam methods, reinforced using magi-craft like Bonding.
However, it was uncertain whether macadam paving in its current state could withstand the heavy loads of future vehicles and aircraft.
If we use magi-craft, repairing asphalt pavement should be fairly straightforward too, Jin mused.
A major flaw of modern Earth's asphalt paving was the difficulty of seamless patching.
When potholes formed, they were filled with fresh asphalt material, but the poor cohesion with the surrounding surface resulted in protruding bumps or sunken depressions, leaving an unmistakable unevenness.
Still, since it becomes impermeable to water, covering massive surface areas requires careful thought.
That might not be an issue in regions with little rainfall, Jin reasoned to himself.
At any rate, ensuring water permeability will be a key challenge going forward.
Ninety percent of asphalt pavement consisted of aggregate gravel, with the remaining ten percent being asphalt in the truest sense. In short, asphalt pavement was simply gravel bound together by an asphalt binder.
By using gravel with larger, relatively uniform grain sizes, natural voids formed between the stones. As a result, those gaps remained even after laying the asphalt, granting it water permeability.
Such was the principle behind permeable asphalt paving.
Its main drawback was that sand and mud tended to clog the voids over time, worsening drainage after several years. Periodic maintenance was necessary to clear out the trapped sediment.
Past noon that same day, Jin and Elsa departed the Shouro Empire aboard the Hurricane and headed for Mitsuho.
"I wonder if a simplified paving method—just pouring asphalt over macadam roads—would be difficult..."
"Yes, My Lord. If it is only intended for pedestrian walkways, that should be sufficient."
Throughout the flight, Jin consulted with Laojun.
"The other question is whether we can refine and improve the asphalt from Mitsuho."
"Yes, I believe that is entirely feasible."
Jin figured that combining it with Hardening and Toughening spells would secure substantial durability.
"And then there's Stabilize as well."
Stabilize was an engineering spell developed by Stearena that made a substance's molecular structure resistant to change.
Specifically, water-soluble substances would no longer dissolve in water, and solids became far less susceptible to degradation from ultraviolet rays.
Since durability was one of the primary weaknesses of asphalt pavement, combining it with such magi-craft should yield significant improvements.
The only problem is that the number of people capable of casting it is limited...
Jin considered that it would likely become necessary to manufacture dedicated construction golems in the future.
Just then, Elsa spoke up.
"Jin-nii, I think if you overthink things too much, you'll lose your way."
"Huh?"
"Jin-nii, you can do so many things. But because of that, you have too many choices. That's why you end up overthinking sometimes."
"You might be right..."
Jin took a moment to reflect, realizing he had indeed let his mind run wild when he was simply on a trip to buy asphalt.
"Besides, it's been a long time since our last visit to Mitsuho."
"Mm."
Unlike in the past, Jin currently lacked official connections in Mitsuho.
Following protocol, they set their course first for Seki Town.
It probably takes its name from 'seki,' as in a checkpoint border gate...
Because the country shared deep ties with the former Japanese native Magus Shuuki Tsetse, place names that appeared to be derived from the Japanese language could be found everywhere.
A massive airfield had been constructed in Seki Town.
"Oh, it's changed quite a bit from the old days."
"It is likely due to the increase in aircraft," Reiko noted.
"That must be it. Traveling from the Shouro Empire by carriage is fine, but from farther away... Ah, though when it comes to transporting heavy cargo, carriages or Golem automobiles are still essential after all."
"Indeed. Let us ask Laojun about Mitsuho's current primary exports."
When Reiko queried Laojun via her built-in manacam, a reply came back in less than a second.
"It appears they are katsuobushi, paper, asphalt, soap, cotton, wooden crafts, and coal."
"So things haven't changed all that much. But coal, you say?"
"Yes. It seems it is not burned for fuel or heating, but rather utilized as a type of chemical reagent."
"I see."
Jin figured that if he asked Saki, she could probably explain its exact chemical applications.
"Understood. Thank you," he said, offering his thanks to both Laojun and Reiko.
"Master, we will soon be directly over Seki Town."
"Oh, is that so?"
Prompted by Hope's report, Jin looked out the window.
"Whoa, so that's the airfield."
Sprawling below was an expansive airfield that looked to be roughly two kilometers on each side.
The Hurricane gradually reduced its altitude, descending smoothly toward the runway.