"Is this the floor we're looking for?"
"It should be."
Jin's group had finally reached the level where they believed the magi-brain managing this mobile base was located.
"Well, let's see what they have waiting for us."
They were currently standing in a circular hall roughly ten meters in diameter. It was narrower than the area they had just left, and the featureless walls made it impossible to determine direction. There were no visible doors.
At that moment, Jin’s body double, Jin D, felt a change in air pressure. To be precise, he felt a drop.
"Is the air being sucked out?"
The current pressure was approximately 0.8 atmospheres, and it was falling by ten percent every second.
"Quite effective... if we were breathing, that is."
"True enough for humans," Jin D replied.
Since there wasn't a single human in the party, a total vacuum wouldn't pose a physical threat.
"The problem is I won't be able to talk to Helente anymore."
Jin D and the Land squad could communicate via their built-in manacams, but Helente was not equipped with one. In a vacuum, conversation would require physical contact to transmit vibrations directly.
I should have installed a manacam in Helente as well... No, there are too many reasons why that would have been difficult, Jin thought.
While he weighed the options, the pressure bottomed out at 0.2 atmospheres. It seemed the system wasn't designed to create a total vacuum.
"We can still manage a conversation at this level."
"Indeed, it appears so."
Voices were faint due to the thin air, but with their superior hearing, it wasn't an issue.
"It's less of a trap and more of a standard measure to eliminate humans or other biological intruders."
"Yes, that is most likely the case."
"Then we should get out of this hall as soon as possible."
"I agree. There is a high probability of a secondary attack."
Jin D and Helente reached a quick consensus to move on. However, they were a moment too late.
"Wait! Is that gas?"
Gas suddenly flooded the low-pressure room. It was hydrogen sulfide. Not only was it lethal to humans, but it was also highly corrosive to many metals.
"Hmph. If it is only this... Decomposition!"
Helente cast her magic. While neutralizing hydrogen sulfide is a complex task in chemistry, magic made it simple. The gas was broken down into hydrogen and sulfur; the sulfur solidified and rained down onto the floor.
"Combine."
Jin D used his magic to "slowly" combine the hydrogen with the trace amounts of oxygen remaining in the room, turning it into water. The hydrogen sulfide was rendered harmless.
"They really aren't pulling any punches."
"No. We must find a way out of this hall immediately."
Despite the five Land units' frantic search, they still couldn't locate an exit. While Jin D focused on the search with the squad, the third wave of the trap was unleashed.
The hall was filled with liquid in the blink of an eye.
"A drowning trap? No... wait, this is acid!"
Helente, utilizing her internal analysis functions, identified the liquid as an acid composed of chlorine and hydrogen—hydrochloric acid.
"They really are persistent."
The walls, floor, and ceiling of the hall were coated in adamantite, which was immune to corrosion from hydrogen sulfide or hydrochloric acid. The Land units' exteriors were made of 64 light silver, protected by an oxide film that hydrochloric acid couldn't penetrate.
Jin D could also withstand the acid without issue, but Helente was a different story. Her exterior was a stainless steel alloy, which reacted poorly to chloride ions. Prolonged immersion in hydrochloric acid would be disastrous for her.
"Let's see, if I remember my chemistry..."
Jin racked his brain for the necessary knowledge.
"Hydrochloric acid... If you electrolyze hydrogen chloride, you get hydrogen and chlorine gas. Land squad, everyone, use Electrolysis!"
"Yes, Master."
The Land units unleashed the lightning-attribute spell 'Electrolysis' from their hands. Being both an elemental and a Craft Magic spell, it was highly precise. A negative charge was generated in their right hands and a positive charge in their left.
Hydrogen ions gathered at the right hands, gaining electrons to become hydrogen atoms, which then bonded into bubbles of hydrogen gas. Simultaneously, chloride ions gathered at the left hands, losing electrons to become chlorine atoms and bonding into chlorine gas.
While natural electrolysis would be a slow process, the Craft Magic accelerated the reaction by forcing the ions to move at high speeds. In short order, the hydrochloric acid was reduced to nothing more than plain water.
"You have my thanks, Jin-dono."
Since they were submerged, sound traveled clearly through the water. Helente offered her gratitude, though the surface of her body was already beginning to lose its metallic luster.
Jin D used Sonar and detected a cavity behind one of the walls.
"Forming."
There was no reason to remain in the hall any longer. Jin D used Craft Magic to warp the adamantite and open a hole in the wall. The water that had once been acid went rushing through the opening.
"I wonder what the brain managing this mobile base thinks of our progress."
"I do not know. The Control Brain on Onogoro Island had lost the capacity for logical thought. It is safe to assume this one is in a similar state."
"Fair point. It's hard to predict the moves of something that isn't thinking straight."
Soon, the water had completely drained away.
"There seems to be a drainage system on the other side."
Jin D reached this conclusion after watching the water get sucked into a drain-like opening in the corner of the floor. For a vessel meant to traverse water, such facilities were a necessity.
"We have to keep moving."
"I will take point," Land 11 announced, and Jin D nodded.
They exited the room in a line: Land 11, Land 12, Jin D, Helente, Land 13, and Land 14. Land 15 maintained a flexible position, acting as a rearguard and scout.
They emerged into a long corridor and began to advance.
"I can't tell if we're going the right way. We might be heading in the exact opposite direction of our goal."
"That is a possibility. However, based on the internal schematics I possess for this mobile base model, we are not entirely off-course."
"Oh? You can tell?"
"Unless the invaders redesigned the entire interior, there would be no reason to deviate from the standard layout."
Helente took the lead, navigating the corridor until she reached a junction and turned left.
"This should be the correct path."
They had apparently been about ninety degrees off their mark. Helente walked with caution, but as Jin D followed behind her, he noticed her movements were becoming slightly labored.
"Helente, are you alright? You're moving a bit stiffly."
"I am fine. It is not yet a malfunction."
It seemed the hydrogen sulfide and hydrochloric acid had taken a toll after all. Corrosion was visible around the seams of her exterior plating. It was possible the damage had even reached her internal components.
"As you are aware, there are other units like me. There is no need for concern."
With that cold reminder, Helente fell silent and continued deeper into the corridor.