<.

The old man is searching for clues by all means at his disposal.

Right now, he is only looking for clues on the surface, such as ventilation openings and entrances.

Therefore, he observes the ground from satellite orbit with his observation satellite .

And he himself is scanning the northeastern part of the continent with his .

There was a possibility of dispatching a land team, but the area to be searched is so vast that even a land team would be dispersed and inefficient, so it has not yet been deployed.

As soon as we find a clue, we plan to deploy a concentrated team.

Yes, that's right.

"That's right."

Jin, who was having dinner with Erza on Horai Island, suddenly shouted.

"Jin, what's wrong?　Did something taste bad?"

Erza tilted her head and asked, but Jin denied it.

No, it's not that... I just had an idea. ............Yes, I think I can do it."

Elsa asks Jin, "What do you mean?

"What kind of thing?"

"I'll explain now.　...... Well, right now you are searching for an underground city on the , aren't you?"

"Yes.

"I've been investigating the upper ground, but I haven't been able to make much progress."

Yes.

So, if you want to search underground, you need to do a .

"Ah."

"But the old man has sealed it off, lest we use the ground search without due care."

"<>...... said that, <> said that too."

"Yeah. So we have to change our ways."

What do you mean?

"That's what ...... means."

Jin begins to explain to Elsa.

He says that the up to now has given priority to the .

It is recommended to change <> to <> and use <>.

He thought that by doing so, he would be able to detect changes ...... in the strata and bedrock of the ground, as well as human-made ...... modifications to them.

This would be an ideal method for his area, which is covered with dense forests and difficult to search visually. ......

"Brother Jin, that's great!"

"Ha ha, thank you. But, you know, we haven't succeeded yet.

That's true.

"...... Well..."

Jin, stop.

Erza grabs Jin by the sleeve and stops him.

Elsa?

"...... tomorrow."

"Uh, yes."

She seemed to sense that Jin was about to go to the workshop.

He sits back down with a wry smile.

"Tonight, we'll be together."

"...... seems so."

The night on Horaijima passed quietly.

* * * *

The next morning, the 21st.

After finishing breakfast, Jin was in his workshop.

With Reiko as his assistant, he is going to build a <>.

"If we rewrite the parameters of the Magi Formula here, we can search for the size of the area instead of the depth.

"Father, do you want to make it variable?"

"That would be better. Can you pass the light silver?

Yes, sir.

The prototype was ready in about 30 minutes.

Okay, let's try it.

Since the device is simply to check the underground, it is not dangerous at all.

Since it is a prototype, Reiko carries it, which is about the size of a box of oranges, and Jin tries it out in the vestibule of the institute.

On the underside of the box, there is a transmitter that emits <> magic waves and a receiver that receives the waves reflected back from the ground.

On the upper surface, there is a < application monitor that displays the results of the scanning.

Most of the larger part is a databank of geo-information, a computing unit for comparison, and an interface for display.

Jin thought that in the field of information processing, the modern earth still seems to be a little ahead of magical engineering.

It seems that magical engineering is not good at > technology.

However, Jin is able to process on the order of micrometers and nanometers with the help of miniature <>.

Aside from that, this prototype was largely a success.

The depth was variable from 1 meter to 10 meters, and the area covered from 10 square meters to 10 It covered an area from 10 square meters to 10 square meters.

"All right, now let's try to make the variable range a little wider.

Jin begins tinkering with the prototype on the spot.

In this respect, magical engineering has the upper hand over earth sciences.

They are more adept at reusing and reworking.

"There we go.

Another test.

"Yes, this is good."

The depth is variable from 0 to 100 meters, and the area ranges from 10 square meters to 1 square kilometer. The range is from 10 square meters to 1 square kilometer.

"I guess we'd better build a new one if we want to extend the range any further. Reiko, let's go back.

"Yes, Father."

Returning to the workshop, Jin builds the next prototype based on the items confirmed in the prototype. It was a , if you will.

This time, it was completed in 15 minutes.

The size of the prototype is as small as an A5-size comic book. However, it will be hard to see the monitor if it is made any smaller.

The test was conducted again in the front yard of the institute.

Naturally, the contents of the survey are the same as the previous one. However, the performance of the device is far superior to the previous one.

"The depth is from 0 meters to 1000 meters, and the area is 100 square centimeters (10 centimeters square) to 100 square kilometers (10 kilometers square). ......Yeah, that's plenty."

The measurement took 20 seconds. It was also fast enough.

"Okay, let's mass produce this and give it to the <> to check."

Jin enlisted the help of the and produced 100 units of this .

He gave them to the and dispatched them to the northeastern part of the .

"So, please do me a favor, old man.

<

The third stage of the survey of the northeastern part of the Rasheer continent, led by the old man in whom Jin has great trust, begins.