"We have received a report from the Mermaid Squad regarding the rock samples."
It was the first update of the day.
"They report that the rocks forming the outer reef are of a different variety than those found on the nearby seabed."
"Hmm. There’s still a chance it’s a natural island," Jin mused. "A volcanic eruption could have produced that kind of variation."
"That is true. However, the combination of several distinct types suggests a higher probability of it being artificial."
"How so?"
"Yes, My Lord. According to the investigation..."
Laojun explained that while the part of the island above sea level consisted of a single rock type, the submerged sections told a different story.
"We have confirmed the presence of granite, basalt, and clay slate within the accessible range."
Jin recognized all three terms. Granite was an igneous rock formed deep underground, while basalt was an igneous rock formed near or on the surface. Clay slate was a sedimentary rock formed from the accumulation of clay. Finding all three in the same location was highly unusual for a natural formation.
"Check if those same rock types exist on the nearby continent," Jin ordered.
"Understood."
The results came back almost immediately. The coastline was basalt, a mountain about three kilometers inland was composed of granite, and sections of the seabed were exposed clay slate.
"That makes the artificial island theory even more likely," Jin said.
"Indeed, My Lord. Next, we will attempt to enter the inner sea enclosed by the rock walls."
Jin, Elsa, and Goose watched the footage being transmitted by one of the Mermaid units. The golems moved with characteristic speed and precision. It wasn't long before they approached the inner sea.
«A barrier has been detected,» Mermaid 566 reported.
"A barrier... More proof that there's something hidden there," Jin noted.
"Jin-nii, if we analyze the pattern of the barrier, do you think it might give us a clue about who created it?" Elsa suggested.
"Good idea. Laojun, get on that immediately."
"Understood."
Five minutes later, Mermaid 566 reported back.
«My Lord, the format is unlike any we have previously encountered.»
"Can you analyze its function?"
«One moment... Yes. We believe this is likely a detection barrier.»
"I see."
A barrier was, essentially, a net woven from mana. While several varieties existed, the "barrier" type used most often on Hourai Island acted as a physical shield. Depending on the mesh size, it could be tuned to block solids, liquids, gases, or a combination thereof.
The challenge in barrier design was selective permeability—for example, creating a field that blocked gas but allowed solids to pass, or vice versa. Since molecules are smaller than solid objects, it was simple enough to use a fine mesh to block solids while letting liquids and gases through.
But blocking gas while allowing solids to pass required a more sophisticated approach. The standard solution involved three keywords: "weak net," "instant repair," and "close contact." When a solid object hit the net, its mass would break through. The net would then cling tightly to the object’s surface as it passed through, preventing any gas from slipping by in the transition. Once the object cleared the barrier, the hole would instantly repair itself.
The barrier protecting this island, however, was a detection type. It was designed to monitor the integrity of the mana net; if the net was broken or disturbed, it would trigger an alarm. It was a perfect setup for guarding a narrow passage.
"So, if we force our way in, we'll trip the alarm."
Jin didn't want to blunder into an unknown situation blindly.
"What to do... Wait, I have it!" Jin thought of a solution. "Laojun, send the necessary transporters to Mermaid 566."
"Understood."
Hourai Island maintained a steady stock of spare magic tools. Laojun dispatched five short-range transporters to Mermaid 566 and her team via a long-range transporter.
«My Lord, the equipment has been received. I am proceeding with the infiltration alongside the other four units.»
Mermaids 566, 567, 568, 569, and 570 then teleported past the detection barrier.
Since teleportation into a liquid medium was impossible, they had to use a tedious workaround: they teleported into the air just above the water, stabilized themselves using force generators, and then slowly submerged. They remained hidden the entire time using Invisible magic. Even the moment they received the transporters had taken place right at the water's surface.
"Well, that's one stage out of the way," Jin said, looking slightly drained.
"It can't be helped," Goose added. "You did insist on keeping things as stealthy as possible."
"True enough."
"Jin-nii, why don't we break for lunch?" Elsa asked.
"She’s right, Father. You need a change of pace," Reiko added.
Prompted by the three of them, Jin finally stood up. He briefly considered having his meal brought to the command room, but knowing it would only earn him a scolding from Elsa and Reiko, he decided to walk down to the dining hall.
By the time Jin returned from lunch, the Mermaid Squad had sent in a new update.
«There are no large fish in the inner sea. We see only small fish, shrimp, and shellfish. The waters are calm, allowing for dense beds of seaweed.»
"Makes sense," Goose said with a nod.
«The interior rock surfaces appear to be entirely basalt.»
"Then the foundation of the island—or 'Onogoro Island' itself—might have originally been a volcanic island," Jin mused. However, geological origins were currently a secondary concern.
«Furthermore, the free ether concentration here is nearly zero.»
"I knew it... It’s a negative singularity."
"If that's the case," Elsa wondered, "it's a mystery how the barrier is even getting its mana."
"I will have them continue the investigation," Laojun stated.
Jin nodded. "Search the seabed thoroughly. Be on the lookout for traps or anything that looks like it's being hidden."
"Yes, My Lord."
It was becoming clear that the survey wouldn't be finished in a single day. As night fell, Jin, Elsa, and Goose left the command room, finished their dinner, and retired to their respective rooms.
"This is frustrating," Jin muttered as he relaxed in the living room of his home.
"What's on your mind?" Elsa asked.
"Progress on the long-period planet and the South Pole survey is slower than I'd hoped."
"Don't rush it. This is work that only you can do, Jin-nii. You need to stay calm."
"Indeed, Father," Reiko added, setting down a cup of hojicha for him. "A breakthrough will surely present itself. For now, please put your mind at ease and rest."
"I suppose you're right. Thanks, Reiko. You too, Elsa."
Jin took a sip of the hojicha and allowed himself a small smile.
"I just realized something. If the long-period planet gets close enough, the gravitational interference could be significant. We might need to prepare for that."
"You mean gravity control devices?" Elsa asked.
"Exactly. We might need to develop some massive, industrial-scale versions."
"Mmm, I see....That gives me an idea. What if we mine resources from the long-period planet and have them sent back here?"
"That’s a thought."
The conversation continued late into the evening as the two discussed future possibilities.