On the evening of July 15, the South Coast Highway was extended from Gidami and completed all the way to the national border.
Naturally, this was all thanks to the hard work of Jin and his golems.
Incidentally, Jin himself had swapped places with Jin D on this day to inspect the highway's finish in person. As a result, Reiko remained closely by his side to guard him.
"Jin-dono! To think you could build such a magnificent road so quickly!"
Minister of Industry Jinzue Mihoyasu had followed behind the golems, observing their work firsthand.
"Their coordination was truly a sight to behold..."
According to the Minister of Industry, he had once wished to pursue the path of craftsmanship in his youth.
"However, I lacked the talent for magi-craft..."
Hearing this, Jin felt a sudden urge to test something. As luck would have it, he had two magi-crystals in his pocket.
"Mihoyasu-dono, do you have a moment?"
"What is it?"
"Well, there's a magi-craft spell called 'Trans Info.' The way it works is..."
First, Jin carefully broke down the process of using Trans Info for Jinzue Mihoyasu, explaining it in simple, step-by-step detail.
"..."
Finally, Jin transferred the fundamental know-how of magi-craft into one of the two magi-crystals to demonstrate.
"'Trans Info.'"
"O-Ohh!"
"Do you understand now?"
"Y-Yes!"
"Then please try transferring the contents of this control core into this magi-crystal."
Jin put him at ease by explaining that this was just a quick aptitude test and that failure didn't matter in the slightest.
"...All right, now!"
Jin gave the signal while simultaneously activating Trace System.
"'Trans Info'!"
"...Hmm."
Trans Info triggered without a hitch.
From what Jin could gauge, Mihoyasu possessed around a level 2 aptitude.
"Mihoyasu-dono, you actually do have a talent for magi-craft."
"I-Is that true?!"
"Yes. You should be capable of mastering beginner-level to mid-level spells."
"Ohh!"
"Now then, try transferring the contents of this magi-crystal into yourself."
Having been guided with such thorough care, Jinzue Mihoyasu cast Trans Info without a shred of hesitation.
"Oh, th-this is...?!"
"...Those are the fundamentals of magi-craft. Please take your time reviewing it whenever you have a free moment."
Having just experienced a taste of the elite Hourai Island magi-craft curriculum, Jinzue Mihoyasu was practically beside himself with excitement.
"O-O-Ohhh! Jin-dono—no, Master, thank you so much!"
"No, please, just treat me the same as always."
Being suddenly addressed as "Master" caught Jin completely off guard.
"...By the way, regarding the land around here."
Once Minister of Industry Jinzue Mihoyasu had regained his composure, Jin brought up another topic.
"Yes. Unlike the terrain leading up to this point, this entire stretch is completely unable to support crops."
He explained that the earth hardened whenever it absorbed water, and crumbled into an ash-like consistency when dry.
"That is why the eastern border was drawn just ahead."
Jin surmised that they had simply decided there was no point in claiming such infertile land as territory.
"Still... hmm..."
Jin was genuinely curious about the condition of the soil.
However, since he lacked specialized expertise on the subject, he decided to just take a sample for now.
Using Forming, he reshaped a nearby rock into a makeshift container and scooped up some dirt.
"Reiko, please load this onto Hurricane."
"Yes, Father....Hope!"
"Yes, Ojou-sama."
Reiko, unwilling to leave Jin's side even for an instant while serving as his bodyguard, called Hope over and handed off the soil sample.
After that, Jin turned back to the minister.
"Well then, Mihoyasu-dono, shall we head back?"
Even as he said so, Jin politely added, "Please allow me to take a brief detour," and steered Hurricane slightly toward the north.
He then gazed down at the mountain below.
"Hmm, just as I thought..."
"Jin-dono, is there something unusual about that mountain?"
"No, it's just that it appears to have been a volcano long ago."
"A volcano?"
At present, active volcanoes were non-existent on Planet Ars.
Hourai Island barely qualified as one, but its nature remained a secret to anyone outside Jin's trusted circle.
"If it really was a volcano, then the soil at the base must be volcanic ash soil..."
Jin had suspected as much ever since hearing that crops refused to grow there.
That realization led to another idea.
"With any luck, we might be able to make concrete... or if not that, at least plaster."
Jin held out hope of replicating something akin to "Roman concrete"—a subject he had some passing knowledge of—which was said to have been made in ancient Rome by mixing volcanic ash.
As proven by the Colosseum standing to this day, the durability of that concrete was virtually unmatched.
However, because Jin's understanding was purely surface-level, he couldn't be certain whether he could reproduce it right away.
Hence, his plan to secure a sample and run experiments back on Hourai Island.
Then, there was plaster.
This was typically made by mixing lime (calcium hydroxide) with glue and hemp fibers, then kneading the mixture with water.
It had the unique property of gradually hardening as the calcium hydroxide absorbed carbon dioxide from the air and converted into calcium carbonate.
Because limestone was abundant in Japan, this plaster had been widely used on the walls of traditional Japanese buildings.
Incidentally, one theory suggested that the Japanese word for plaster, shikkui, was derived from sekkai, the word for lime.
After flying Minister of Industry Jinzue Mihoyasu back to the royal capital of Quonale aboard Hurricane, Jin used the pretext of returning the golems to pass back through the eastern outskirts of the highway before returning to Hourai Island.
"...And that's the whole story."
Jin consulted Saki, one of the Jin Family members on Hourai Island.
"Kufu, I see. In short, you want me to look into whether we can use this volcanic ash soil to make building materials, right?"
"Exactly. I know you've got your hands full, but do you think you could handle it?"
"Of course. There's no way I'd pass up on a project that sounds this fun."
Saki accepted with a chuckle.
"Speaking of having your hands full, aren't you just as busy, Jin?"
"Well, yeah. But I have Laojun and Deus Ex Machina helping out, so it's not so bad."
"Kufu, let's both do our best without pushing ourselves too hard."
"Yeah, definitely."
With their goals set, Jin and Saki each headed off to their respective workshops to get down to business.