On October 20, the < that had gathered on Horai Island returned to their respective posts.

< Zion, <> Rhodoth, <> Ludmilla, and the others returned to the .

Reinhard, Berche, Luis, Bina, Goose, Saki, Tor, Stearina, Vivian, Licia, Marcia, Rodrigo, Hannah, Martha, Mirówna, and others, and <> 700 672, now known as , returned to the planet Hale with their adopted daughters Neige and Rouge.

In other words, Jin and Erza are the only ones left on Horai Island.

"It's been a while since we've been alone.

huh?

Jin wanted to relax a little since things have been so hectic so far.

However, being the poor man that he is, after just half a day of relaxing, he couldn't spend any more time in idleness and started to want to cook something.

"Hmmm......... I'll have to think of some new materials. ......"

Erza giggles as she watches Jin muttering such things while lounging around on the porch of their <, doing the dishes.

<, which seems to be a mass-produced type made by the .

It was light, easy to work with, and its strengthening by magic power was remarkably effective.

"Let's try to organize our thinking: ......"

Jin lies down on the porch, looking at the sky, and thinks to himself. It is easier to organize his thoughts when he says them out loud.

I think someone said that when the brain organizes information that comes in through the ears, a different part of the brain is activated than the thinking part. ......" He puts his thoughts together, thinking in a corner of his mind.

"I think the basis of the idea is to raise the level of <>.

Jin is convinced that this is the way to go when it comes to mass production.

"For that purpose, ......"

There is a problem that high technology and knowledge are required to produce the product.

In addition, it was thought that dedicated facilities would be needed for mass production.

"The former problem can be solved by constructing a well-structured theory and training engineers. The latter problem can also be solved by adding a simplified guide to the <> of the equipment: ......"

In a leisurely state where he was not pressed for time, Jin's ideas came together one after another.

* * * * * * * * * * * * * *

"Jin-bro, tea.

"Oh, thank you.

Before he knew it, it was almost 3:00 p.m. and Erza brought tea and tea cakes to the porch.

Elsa sat down next to Jin. The atmosphere of a mature couple was somehow in the air.

Incidentally, Reiko stayed in the next room so as not to disturb them.

* * * * * * * * * * * * * *

"Thanks for the tea."

Jin finished his tea and put the teacup on the tray.

"Did you come up with something at ......?"

"What?　Do you know what I was thinking about?

"Nope. "Well, that's my wife."

I see. ...... you're in a lot of trouble.

No, actually, it was in my voice.

"Oh, ...... you're talking to yourself."

"Yeah."

Jin scratched his head and began to explain to Erza the thoughts he had just collected.

"I've stopped obsessing over alloys."

Jin explained that he would first of all like to develop this idea in a direction that would be useful to the world.

"If it's the strongest metal material, we already have it."

is it.

It is a molecularly compressed magi-adamantite, and the specific gravity varies depending on the compression ratio, but the standard compression ratio is 10, and the specific gravity is about 200. The strength of the material is 20 times greater than that of the standard material.

The material used for Reiko is five times stronger than the standard material.

A quiet word.

"I was thinking that we could use <> instead of sticking to alloys."

"Composite?"

"Composites?" "Yes. ...... For example, there's <>, right?"

Yes.

"What if we think of making that foam part contain particles of magicrystal instead of air?"

"...... is possible enough."

"Right?"

Jin explained, "If we can make that <> contain enough <>, it will be able to strengthen magic power all the time.

"Indeed. Jin, you're right.

"Haha, thank you. I was just thinking about it and came up with the idea.

"Well, you can't put too much work into it.

"I know that, but ...... it's not so easy."

Jin smiled wryly.

"Back to the subject, I think we can do it by using <> and <>. Or maybe we can make it in the weightless state in space ......."

"Hmm, sure. ...... but it is not common to make it in space."

"......Well, well, that's the first step."

What's next?

I haven't thought about it yet.

"I see."

Now Elsa laughed.

Then the old man called.

<>

"Yes, that's good. You are reporting on ......<>?"

<

"Then let me hear it even more."

"Then tell me more about it."<"I have learned that the seems to have been abandoned, but there are still many mysteries, so I had instructed the old man to conduct additional investigations.

Therefore, Jin did not have a choice but not to ask.

> is a separate facility, unrelated to the upper levels .......

"Huh?　What do you mean?"

The old man has put in 50 < to check it out: .......

First of all, they were built at slightly different times.

<

"Oh, it's too old to be accurate."

"There is no passage, is there not?

<

<. The reason why there are no traces of the third and fourth basement floors is because I thought that they were buried because they were no longer in use, but then it would not be surprising if there were traces of stairs and elevators.

<>...... must have been a base or a facility at that time, although I think that it was the reason why they built another facility under it>>.

The reason is that the floors are not out of alignment.

"I see."

<< or belonged to the same .

"Yes, I understand."

< do. This may be because they took their belongings to an underground city they built on the . We have no way of knowing for sure at this point.

The old man concluded, "There are so few things left that we can't even try to find out.

"Okay. Thank you."

The old man's report was finished.

Jin once again thought of the that he thought was in the .