Hourai Island, August 10.
Wisps of clouds drifted across a blue sky, and a cool morning breeze blew in from the sea.
"Good morning, Elsa."
"Good morning, Jin-nii."
Jin and Elsa exchanged morning greetings in the washroom of the house. Splashing their faces with cold water woke them up completely.
"Father, here is your towel."
"Ah, thank you."
Jin took the towel from Reiko and dried his face and hands. He then spoke to Elsa, who was returning her own towel to Edgar.
"It’s finally tomorrow."
"…Mm."
Engaged in quiet conversation, the two humans and their two golems left the house and headed toward the laboratory’s dining hall.
"Good morning, My Lord."
"Morning."
Perido 1 was already there, having just finished preparing breakfast. Naturally, she had monitored when Jin woke and washed his face, calculating his arrival time to ensure the food was ready at the perfect moment.
"Good morning, Jin-kun."
"Hey, good morning."
Vivienne and Saki arrived shortly after. With the wedding scheduled for tomorrow, several members of the Jin Family had already gathered on Hourai Island. Reinhard and his wife, Earl Kuzuma and his wife, and Lishia were expected to arrive later tonight once they finished their various administrative duties.
"Morning."
"Good morning, Jin."
Besides Vivienne and Saki, those currently on the island included Marcia, Rodrigo, Goose, and the married couple Toa and Stearena. Mine was also present, having been here for some time to personally attend to Elsa.
『My Lord, good morning. I received a communication from Milowina-sama earlier. She is expected to arrive around noon, our time.』
Laojun’s report came in as Jin was eating. He listened while finishing his meal.
"That was delicious."
As Jin finished his food and began sipping his hojicha, Saki and Vivienne finished their meals as well. Elsa followed suit shortly after.
"So, Jin, what’s on the agenda for today?" Saki asked, carrying her tea cup over to Jin and Elsa’s table.
"Well, since all the preparations are done..." Jin replied, "all that's left is to go meet Milowina."
"Heh, is that so? Personally, I was hoping to hear a more detailed explanation about that 'liquid metal' you found," Saki said.
"Oh, I would like to hear that as well," Stearena added, joining them with her own cup of tea.
"Jin-kun, I want to know too!" Toa shouted from across the table, not quite finished with his food yet.
Jin gave a wry smile. "Alright then. Let's spend the morning discussing that."
"Well then, shall we get started?"
Nearly every member of the Jin Family currently on Hourai Island was gathered in Jin’s workshop. The only exceptions were Elsa—who already knew the details of liquid metal—and her mother, Mine. The two of them were likely sharing a private mother-daughter moment before tomorrow’s ceremony.
"To start, I assume everyone is here for the lecture on 'Liquid Metal and its Applications'?"
No one objected; on the contrary, every face looked eager for the explanation.
"Very well. First, the liquid metal is, in fact, mercury. I trust everyone understands that?"
The group nodded silently.
"Liquid metal is a magi-isotope of mercury. In other words, you could call it magi-mercury rather than just plain mercury."
Jin explained that the relationship was similar to that between silver and mithril.
"In liquid metal, the neutrons within the mercury’s atomic nuclei have been replaced with magi-particles. As of now, we only know that it originates from the 'Southern Island.'"
"The 'Southern Island,' huh..." Marcia murmured with interest. She clearly still wanted to see the place for herself.
"Regarding its physical properties, it is almost identical to standard mercury. Its specific gravity is approximately 13.5, and its melting point is roughly minus 39 degrees Celsius."
Most of its other characteristics mirrored ordinary mercury as well.
"Since its chemical properties are also nearly the same, it must be handled with extreme caution."
Jin emphasized the dangers, explaining that if the metal vaporizes, it is easily absorbed through the lungs. Once inside the body, it binds with substances like hemoglobin and becomes highly toxic.
"Especially you, Saki," he said, fixing her with a firm look. "It is far more dangerous than that time you got a rash from urushi."
"Ah, ahaha... you're worrying too much, Jin," Saki replied with a sheepish laugh, though her expression showed she had taken the warning to heart.
"It’s better to be overly cautious than not. If it accumulates in the brain, it seems to impair the ability to regulate emotions."
Jin used the cases of Jix and Gunno to illustrate the potential for instability.
"However, the decisive difference between this and ordinary mercury is how it reacts to magic."
He shifted the lecture toward the magi-craft perspective.
"This metal conducts magic exceptionally well. In this context, 'magic' refers to mana or the energy derived from mana."
Stearena leaned forward, captivated.
"Because of this, 'Forming' the liquid metal is incredibly simple. That is likely why it was used in the Fluid Form Drive."
The advantages were clear: it eliminated the need for magi-nerve wiring and possessed the ability to store mana. However, Jin noted a significant catch.
"The drawback is its narrow operating temperature range. This is a fatal flaw, even setting aside the toxicity."
"That makes sense," Saki noted. "It wouldn't be usable in environments where Frost Dragons live, would it?"
She was recalling their journey to the Arctic Circle—north of even the demon territory—to find the shed skin of an Ancient Dragon. They had encountered temperatures as low as minus 40 degrees Celsius during that expedition.
"Exactly. It’s also vulnerable to fire magic..."
It was a dangerous combination. If the mercury were to vaporize due to heat, the resulting toxic clouds would be catastrophic.
"I still think it has its uses, though," Marcia chimed in. "Jin, couldn't you think of a way to compensate for those weaknesses?"
"Well... I suppose there are a few workarounds," Jin conceded.
"Let’s hear them!"
"Sure. To start, you could build a heater into the system to handle low temperatures. That’s a simple fix."
That was a solution most of them could have envisioned.
"For high temperatures, you would just need to integrate a cooling system." Jin added that this would, of course, slightly lower the overall efficiency of the drive.
"But..." Jin’s expression clouded over. "There’s no easy fix for the toxicity of mercury itself. Ultimately, we would need to find or synthesize a safer version of liquid metal."
"Heh, that sounds like a fun research project," Saki said, her eyes sparkling.
"Yeah, it really does," Toa agreed.
"Feel free to research it, but please, be extremely careful about poisoning," Jin insisted, unable to let the matter rest.