It was the day after Jin had crafted the force pump in the Klein Kingdom and saved Tia.
Jin had returned to Hourai Island and was currently in conference with Laojun.
They were discussing the next phase of the plan following the deployment of the Watcher surveillance satellites. Reiko was present, as were Elsa and Saki.
"…So, My Lord, are you suggesting that the depths of the earth still hide many mysteries?"
"Exactly. Especially the underworld of the Former Leonard Kingdom. For Giga Ants like those to emerge is, to say the least, abnormal."
"That is certainly true. So, specifically, what do you intend to do?"
"…Jin-nii, are you going to use the Mole?" Elsa asked, anticipating his move.
The Mole was a subsurface exploration Magi Machine Jin had previously crafted. Resembling the shield machines used for tunnel excavation on modern Earth, it was a cylinder two meters in diameter and three meters long. It could dig using either a Dig magic tool or mechanical excavation utilizing hyper-adamantite tipped bits.
"Hmm, that’s a bit too extravagant… or rather, I think it’s simply too large," Jin said, dismissing Elsa’s suggestion with a pensive look.
"Jin, what do you mean by that?" Saki chimed in.
"I mean, if we’re just conducting a survey, a smaller machine would be more efficient."
"Ah, I see. You’re talking about the size of the tunnel it leaves behind?"
"Right. If we don’t need people to follow inside afterward, I think it can be even smaller."
The original Mole had been built to its current dimensions specifically for the environment of the Inado Mine. Jin explained that he wanted something scaled to fit a Mini-Smith or a Little-Smith.
"…In that case, the cost wouldn’t be nearly as high."
Elsa was convinced, so they immediately began exploring that line of reasoning.
"The primary objective is an underground survey of the Former Leonard Kingdom."
"Those magical beasts really are abnormal," Saki agreed. She had heard the reports, and she was even using the Giga Ant's digestive fluid as a reagent to evaluate the chemical durability of various materials.
"Remember when we used the Mole to investigate the Inado Mine and found that facility that looked like a Gigant Peeder farm?"
"…I do," Elsa nodded.
"I suspect there might be something similar under the Former Leonard Kingdom. The northern part of that country borders Kaina Village, after all."
"Ah, that makes sense. I can see why you’re worried, Jin," Saki said, empathizing with his concerns.
"And there’s one more thing. I’m genuinely curious about the internal structure of this planet."
Jin stole a glance at Saki.
"It seems the reason Hourai Island grew larger compared to the Predecessor’s time was due to volcanic activity, but there are no active eruptions now. Even looking at the completed world map, there aren't any active volcanoes. Given that this planet is small, I suspect it might have already cooled down quite a bit, perhaps all the way to the core."
"Hmm? What do you mean by that, Jin?"
Saki didn't seem to follow. It was only natural, as her scientific education was currently only equivalent to a primary school student’s back in Japan.
(I wonder if I could make a magic tool to grant Saki a higher level of Trans Info?) Jin wondered.
"Well, you see, even if a planet's surface is cold, the interior is usually hot. That’s why volcanoes erupt and hot springs bubble up."
"I see, I see."
"And since this world is small… at least, compared to the planet I used to live on… I thought the core might have cooled significantly."
Since Jin’s own knowledge of geology was roughly at a middle school level, his explanation was a bit clumsy. Furthermore, he wasn't even sure if it was meaningful to compare the planet Ars to Earth.
"In short, I want to see what it's like underground. How magi-crystals are formed, what kind of resources are down there—things like that."
This explanation was much more to Saki's liking.
"I get it! Jin, let's investigate! Come on! Right now!"
It was Elsa who restrained the over-excited Saki.
"Saki-nee, calm down. We’re discussing the magic tools we need to build first."
"O-Oh, right. My apologies."
With that, they began hammering out the specifications under Jin’s lead.
"Ten centimeters in diameter and thirty centimeters long."
It was roughly the size of a large tea canister.
"Power source: a micro magi reactor."
This would be an ultra-compact magi reactor manufactured by the Mini-Smiths. Even a top-tier magi craftman wouldn't be able to analyze it. Even if it fell into the wrong hands, they wouldn't be able to reverse-engineer it.
"Propulsion: a force generator."
It was the most efficient method available.
"We’ll install a magic eye to transmit information back to us."
This was a necessity, given that the primary goal was a survey.
"To ensure the technology isn't analyzed for malicious purposes if it's captured, we'll build in a transporter, a self-destruction mechanism, and a self-explosion device for the worst-case scenario."
The transporter would be set to return the unit to Shinkai. If that failed, it would trigger its internal destruction. If absolutely necessary, it could self-destruct violently. Protecting their secrets was the top priority.
The specifications continued to fall into place.
"I want to put one golem equivalent to a Mini-Smith on board to handle any unexpected situations."
Saki raised an objection to this.
"Hmm, Jin, is that a good idea? If something happens that the onboard equipment can't handle, do you really think a Mini-Smith could do anything?"
Jin countered her point.
"They can perform field repairs if something breaks. Besides, they’re fast and can use Invisible, so I doubt they'd get caught."
"I… see. If you say so."
Jin added that they simply had to accept that level of risk. Finally, they reached the most critical part: the method of "digging."
Moving through a solid object meant repeatedly moving the material in front of the machine to the rear. This was easier said than done.
A standard drill carves a hole by using the spiral grooves on its sides to discharge debris. When digging a tunnel, one needs a conveyor system to remove the fragments of rock crushed by the machine. Even if they used a laser to vaporize the rock, the resulting gas would still need to be vented.
"Hmm, how to handle this?"
It was a difficult problem. The primary reason for Jin's hesitation, however, was "stealth."
He was worried that if there was some kind of facility underground—something like the magi-brain once created by the Failure—he didn't want to alert it. Mechanical digging would create vibrations and noise that could easily be detected.
"Let’s go with the transporter gun approach."
"…Jin-nii, how would that work?" Elsa asked, tilting her head at the unfamiliar terminology.
"Well, we’ll mount a device identical to a transporter gun on the tip, and we'll simply teleport the rock in our path to the area behind the machine."
The teleportation distance would be exactly the length of the Mini-Mole.
"Wait, so you mean it teleports ten centimeters of rock to the back, moves forward ten centimeters, then teleports the next ten centimeters…?" Saki clarified.
"Exactly. Since the teleportation distance is so short, the mana consumption will be minimal."
"So it moves in bursts?"
"That’s the idea. It will accumulate mana via the micro magi reactor, teleport, move forward, accumulate more mana…"
"It might take a while, but it sounds fascinating."
"Mm. I want to build it."
"Alright, let's get started."
Thus, the production of the Mini-Mole began.
Jin privately thought it resembled an earthworm more than a mole, but he didn't say so aloud.
"How are the preparations for the ceremony?"
"They proceed apace, Your Majesty."
Inside the Royal Castle of the Celuroa Kingdom, King Richard was receiving a report from his subordinates while eating lunch.
"I see. Heh heh heh… I can’t wait to see the looks on the faces of the other nations' representatives."
The city of Dali was a labyrinth of canals, much like Venice, where waterways served as the primary arteries of travel. New models of small vessels were already bobbing in those channels.
"Ships, airships, golems. We shall demonstrate once again to the world that Celuroa is the undisputed leader of this continent."
King Richard grinned and drained his glass of wine in a single gulp.