On January 26th, Jin returned to Horai Island and was greeted by his beloved wife Elsa and Saki, who was very excited to see him.

"Brother Jin, welcome back," Saki said to Elsa.

Saki said to Elsa, "Brother Jin, welcome home,

"Jin, the mask is ready!"

She said at the beginning of her speech.

I helped, too."

Erza added.

"Well. I'm looking forward to it.

Jin immediately went to the workshop.

"Look!"

"Oh, this is nice."

Saki showed him a three-dimensional mask like the ones Jin had seen in modern Japan.

"If you put a pad on your nose, it will be comfortable and not fog up even if you wear glasses like me.

"Yes.

The masks come in five different designs and two colors, white and light blue.

"They are made of a blend of cotton and Maggi polyethylene fiber. The storage case has a < effect, so you can put it away and it will be clean the next time you use it.

The < effect also has a sterilization effect, so the product is clean and sanitary.

"That's very well thought out."

"Cost-wise, the storage case is going to be a bit expensive, though."

"Maybe they should be sold separately."

If the masks are sold as a set and separately, it is possible to buy just the masks again, and if the storage case breaks down, it can be dealt with.

"Yes, that's right. I think we can decide on that when we discuss the sales format."

"Yes, that's right. You've done some research on asphalt emulsion at ......, haven't you?"

"Of course!　That's not really something I want to show you here, so let's move it to another place.

So Saki, Hitoshi, Elsa, Reiko and the others came to the temporary tent outside the laboratory.

"Asphalt emulsion is quite smelly. I thought it would be a nuisance at mealtime."

"That's true."

It has a peculiar petroleum smell.

That's why we're doing it here.

Jin and the others were led into a large tent.

"We've been waiting for you.

"Oh, <> is here. How are you?

Yes, everything is fine.

Good, that's good.

Before he could begin his report, he pointed to the ground.

"Over there, there is a test pavement of about one meter square. Could you try it out first?"

"Let's see..."

Hitoshi, too, looked interested and climbed on the pavement.

"Yes, this is definitely asphalt pavement.

It was very close to the asphalt pavement that Jin remembered.

"Kuh-huh, I see, that's good.

Saki seemed satisfied to hear Jin's words.

"I heard from Jin that asphalt emulsion is a version of the original asphalt, right?"

Jin nodded.

There is no way to know what kind of existed in modern Japan, but I can analyze this world-made that I bought the other day.

"Originally, asphalt was supposed to be heated to 160 degrees Celsius, melted into a sludge, and paved over, but this is supposed to be used at room temperature," Saki said.

Saki says asphalt is a highly viscous hydrocarbon liquid ...... viscous body.

"And you dilute it with a solvent."

The solvent is volatile even at room temperature, so after a day of paving, it will regain its original viscosity and can be used as asphalt pavement.

"And so far, it's within the bounds of common sense."

Saki laughed and clasped her palms together.

"I'm going to report the results of my various experiments with , which my assistant lent me!"

"Oh!　That's going to be fun."

"Well, let's have a look at this one, shall we?"

Saki pointed to another area of pavement.

"This area was paved with asphalt emulsion and then coated with a toughening agent. Do you see the difference?"

"<>...... Oh, it's not as tough!"

"<> was applied, so it's not surprising. We used half the amount of asphalt emulsion.

That means we can cut costs, Saki said.

"That would be nice."

Jin, who is planning to use his money to help turn the economy around, thought that if he could save money, that would be great. He could put that money somewhere else.

"Now, I have a favor to ask of Jin here."

"Yes?　What is it?"

"Can you make a softening agent to soften the asphalt emulsion on this pavement?

That would make it easier to remove the pavement and repair it, Saki said.

"I see."

Since this is engineering magic, it is certainly Jin's domain.

"So it doesn't work on the ...... gravel, but only on the asphalt emulsion that's attached to it."

Jin thought for a moment.

"Yes, it can. ...... I mean, asphalt emulsion is a hydrocarbon, right?"

"Yes, it is. That's what they use to bind the gravel together.

"So, the target should be hydrocarbons, right?

Jin guesses that he can soften the hydrocarbons by adjusting them to <, and immediately begins to formulate the <.

It is necessary to think about the <, but Jin is not an ordinary mage.

"...... Okay, yes, it's done."

"Are you sure?"

"Really?" "Yes. Can I try it?

Jin pointed to the pavement where he had hung the toughened pavement.

"Of course. Please give it a try and show me.

"Sure. ......<"

"Whoa!"

Jin's newly created melt has made a mess of the paved asphalt.

"It's engineering magic that melts the hardened glue and adhesive once again."

The gravel is unaffected, so the overall appearance is that it has crumbled.

"...... Hmmm, I see. But the asphalt emulsion that holds the gravel together has not returned.

Saki said, to which Jin replied with a wry smile.

"You can't put the volatile components back in.

"That's right. ...... can you get this back to the hardness it was when it was paved?"

"Of course. Of course. Since this effect is reversible, we have considered such engineering magic at the same time. ......<>...... see?

After applying <>, the asphalt returned to its asphalt-like hardness.

"Yes, yes, good, good, good. Can you also apply ...... to it?"

"Of course you can. ......<>"

"Oh!　You're a gin, aren't you? Now we know that paving, durability, repair and maintenance can all be done with engineering magic.

This means that no paving materials are wasted and no waste materials have to be thrown away.

"It's environmentally friendly, isn't it?"

"Yes, it is."

Jin nodded in agreement with Saki's comment.

"Now we can pave the circuit in the Kingdom of Franz.

Jin reaffirmed his thoughts from the other day, "We'll be spending a lot of time on construction work for a while.