On January 26, when Jin returned to Hourai Island, he was greeted by his beloved wife, Elsa, and an eager Saki.
"Welcome home, Jin-nii."
In stark contrast to Elsa's gentle welcome, Saki burst out the moment she saw him:
"Jin, the masks are finished!"
"I helped too," Elsa chimed in.
"Oh? I'm looking forward to seeing them."
Without delay, Jin headed toward the workshop.
"Look!"
"Ah, these are fantastic."
What Saki presented to him were contoured, three-dimensional masks, much like the ones Jin remembered from modern Japan.
"If you place a pad right where it sits on the bridge of your nose, it keeps your glasses from fogging up. It's super comfortable, even for someone who wears them like me!"
"That's definitely a plus."
There were five different designs, available in two colors: white and light blue.
"They're woven from a blend of cotton and magi-resin fibers. On top of that, the storage case is enchanted with Cleanup, so whenever you tuck the mask away, it's completely sanitized and fresh the next time you need it."
Since Cleanup carried a sterilization effect as well, the masks remained pristine and hygienic.
"You've really thought this through."
"Cost-wise, though, the case might drive up the price a bit."
"We could always sell them separately."
If they offered them both as a set and individually, customers could easily buy replacement masks on their own, and anyone whose case broke wouldn't have to buy an entirely new bundle.
"Yeah, good point. We can hash that out when we decide on how to sell them."
"Right....So, did you make any progress researching the asphalt emulsion?"
"Of course! It's a bit awkward to show you in here, though, so let's head somewhere else."
With that, Saki led Jin, Elsa, Reiko, and the others out to a temporary tent set up outside the laboratory.
"Asphalt emulsion gives off quite a strong odor, you see. I figured it would bother everyone around mealtime."
"Makes sense."
It possessed a distinct, petroleum-like smell.
"So we've been working on it in here."
Saki guided the group inside the large-class tent.
"Welcome back, Master."
"Oh, so this is where you were, Enju 1. How are you holding up?"
"Yes, there are no issues whatsoever."
"Glad to hear it."
Before getting to the rest of her report, Saki pointed toward the ground.
"Over there, we paved an experimental section about one meter square. Why don't you try stepping on it first?"
"Let's see."
Intrigued, Jin stepped onto the paved patch.
"Yeah, no doubt about it—this is real asphalt pavement."
Underfoot, it felt almost identical to the asphalt roads etched into Jin's memory.
"Kufu, is that so? That's great to hear."
Hearing Jin's reaction, Saki beamed with satisfaction.
"Asphalt emulsion, as I gathered from what you told me, Jin, is basically standard asphalt that's been 'diluted,' right?"
Jin nodded.
While there was no way to inspect the exact asphalt emulsion used in modern Japan, they were fully capable of using Analyze on the local asphalt emulsion recently purchased in this world.
"Standard asphalt is usually heated to 160 degrees Celsius to melt it down into a thick sludge before being poured over the ground to pave it, but this formulation is designed to be workable at room temperature."
According to Saki, asphalt was a viscous hydrocarbon liquid—a thick, sticky mass.
"And that's thinned down with a solvent."
Because the solvent was volatile even at room temperature, letting the laid pavement cure for a full day allowed it to regain its natural viscosity, leaving behind functional asphalt pavement.
"And that's just the basic theory."
Saki grinned and clapped her hands together.
"Now, let me tell you about everything I tried out with Enju 1 while you let me borrow her as an assistant!"
"Oh! I can't wait to hear it."
"Well then, take a look over this way."
Saki pointed to another paved section.
"On this patch, after laying down the asphalt emulsion, I had Toughening cast on it. Can you tell the difference?"
"Analyze... Oh, the durability is on an entirely different level!"
"Well, that's only natural since Toughening was used. But get this: we only needed half the usual amount of asphalt emulsion."
In other words, Saki explained, it would significantly cut down on material costs.
"That's a huge help."
While Jin was more than willing to spend his own gold to stimulate the local economy, saving resources where possible was always a plus. Any money saved could simply be redirected toward other projects.
"Now, that brings me to a favor I'd like to ask, Jin."
"Hm? What is it?"
"Could you create a Softening spell that softens only the asphalt emulsion in this pavement?"
If they had a spell like that, Saki explained, stripping up old pavement or making spot repairs would become remarkably easy.
"I see."
Since it involved magi-craft, it was squarely within Jin's realm of expertise.
"Hmm... So it shouldn't affect the gravel at all—only the asphalt emulsion binding the stones together."
Jin pondered the concept for a moment.
"Yeah, that's doable....After all, the asphalt emulsion is made of hydrocarbons, right?"
"Yup, exactly. It uses those to bind the gravel together."
"Then all we have to do is set hydrocarbons as the target."
Deducing that he simply needed to calibrate a Softening spell tailored to hydrocarbons, Jin promptly began weaving the magi-formula.
Under normal circumstances, one would need to carefully map out the entire magi-sequence in advance, but Jin was far from an ordinary magi.
"...All right, yeah, that should do it."
"Really? Already?"
"Yeah. Mind if I give it a try?"
Jin pointed toward the section reinforced with Toughening.
"Of course! Please, show me how it works."
"Understood....Melt."
"Whoa!"
Jin's newly formulated Melt spell instantly reduced the cured asphalt into a loose, crumbly mess.
"It's a magi-craft spell designed to re-liquefy set adhesives and bonding agents."
Because it left the gravel untouched, the entire structure looked as though it had simply fallen apart.
"...I see, I see. But the asphalt emulsion binding the stones together hasn't returned to its original state, has it?"
Jin chuckled wryly at Saki's observation.
"I can't magically bring back volatile components that have already evaporated into thin air."
"Yeah, fair point....Can this be restored to the hardness it had when it was first paved, then?"
"Of course. The effect is reversible, so I worked out a companion magi-craft spell to handle that at the same time....Hardening... There."
The moment Jin cast Hardening, the surface regained the solid, unyielding firmness characteristic of cured asphalt.
"Ooh, that's great! Really great....Can you cast Toughening over it again, too?"
"Naturally....Toughening."
"Incredible! That's Jin for you. With this, we know that paving, boosting durability, and performing repairs or maintenance can all be handled entirely through magi-craft."
This meant paving materials would never go to waste, and there would be no need to haul away mounds of discarded rubble.
"It's remarkably eco-friendly."
"Yeah, it really is."
Jin nodded in agreement with Saki's remark.
"With this method, paving the circuit in the Kingdom of Franz shouldn't be an issue at all."
Looks like my days are going to be consumed by construction work for a while, Jin thought, reaffirming what he had realized just the other day.