"Hmm."
"..."
Jin and Elsa were still deep in thought.
"It would be relatively simple if the shape were fixed," Jin muttered.
With something like a Plasma Sword, the barrier could be maintained in the shape of a blade precisely because its form was predetermined.
"A barrier, huh... Wait a minute."
"Jin-nii, the barrier cushion car."
The same thought seemed to have struck them both at once.
"If the goal is simply protection against pathogens, this might work," Jin said.
"A soft barrier," Elsa added.
"Eh?"
"Eh?"
They looked at each other, realizing their ideas were slightly different.
"Uh, you go first, Elsa."
"...No, you first, Jin-nii."
"I—I see."
Since there was no point in going back and forth, Jin voiced his idea.
"I realized we don't necessarily need to stick to conventional barriers. What we need is a 'Sterilization Barrier'."
In short, it would be a barrier that sterilized anything that entered its effective range.
"I see. That makes sense."
As Elsa nodded, Jin asked her in turn, "And what was your idea?"
"To take a flexible barrier, like the one used in the barrier cushion car, and shrink it down."
"I see... By doing that, depending on the settings, the barrier would form itself along the surface of the body."
"Mm."
Jin and Elsa began their consultation again. Laojun joined the conversation as well.
『If we limit ourselves to the initial objective—inviting Milowina-san to Ars—then My Lord's "Sterilization Barrier" would be the most appropriate choice.』
Laojun stated that it was both highly feasible and reliable.
Neither Jin nor Elsa had any objections to that. In fact, that was the plan they intended to pursue. The real interest now lay in the potential applications of Elsa's idea.
"...If we use a barrier conforming to the body's surface as a base, and then generate another layer of barrier from there..."
"As expected of Jin-nii. That is exactly what I was thinking."
『My Lord, with that method, any kind of barrier could be generated to perfectly follow the contours of the body.』
It was a complete change in perspective.
A low-strength barrier was prone to deformation. The barrier cushion car utilized that property to absorb the irregularities of the ground. If one gradually reduced the size of a barrier enveloping a subject, it would eventually come into contact with the subject's body.
What would happen if the barrier were shrunk even further?
If the barrier was permeable to air but impermeable to solids, it would begin to deform—conforming perfectly to the subject's body. If they were wearing clothes, it would follow the surface of the fabric as well.
"This barrier is, of course, generated by the action of free ether," Jin said, explaining it to Elsa as if to confirm the logic for himself.
"Mm. Therefore, it can be used as the origin for a different barrier."
"Wow, Elsa, that’s incredible! I hadn't even considered that approach."
Jin realized that if this concept were applied, multi-layered barriers—or rather, composite barriers—could be created with ease.
『Indeed. Currently, the origin point is the control core used for generating the barrier. If we try to deploy two or more types of barriers simultaneously, minute errors occur, making it impossible to achieve a perfect overlap.』
"But by applying Elsa-sama's idea, we can eliminate that margin of error," Reiko added, sounding impressed.
Jin, Elsa, Reiko, and Laojun discussed the possibilities of this method for a while, but they ultimately decided to focus on their original goal first.
"First, the Sterilization Barrier."
"Mm. Jin-nii's approach is better suited for this."
Their reasoning was that if the same result could be achieved, the simpler method was superior.
"Was it... Autumn's Razor?"
The correct term was Occam's Razor, also known as the principle of parsimony. It was the idea that when explaining a law or solving a problem, one should shave away unnecessary elements—hence the "razor."
They wanted to bring Milowina over, but for her, the world of Ars would likely be teeming with pathogens to which she had no resistance. That was why they were developing the Sterilization Barrier.
"We probably need to consider bacteria inside solids as well," Jin noted.
He was referring to food.
『But wouldn't that ruin the flavor if we go too far?』 Laojun asked. He was thinking of fermented foods.
"That should be fine. It just means that even if she eats it, her intestinal bacteria won't be supplemented."
The same applied to liquids. However, they had to ensure it had no effect inside the body, or it would end up sterilizing Milowina's own essential gut flora.
"Elsa, what do you think?"
"...Mm, I think I can do it."
Elsa quickly sketched out a magi-sequence on a piece of note paper.
"Yeah, I see. This should work. Originally, with the exception of things like healing magic, magic can't affect the inside of a living body anyway."
"Right. Healing magic is special. But Sterilization as Craft Magic..."
By its very nature, it did not affect the interior of the human body.
In this way, the Sterilization Barrier was completed by that evening. It was a pendant-type device, meant to be worn around the neck.
"This seems like it would be very effective for surgical operations, too," Elsa remarked.
"Ah, definitely. Shall we take one to Sally-sensei as well?"
"In that case, it might be better to give it a bit more versatility so it can sterilize an entire room."
"Good point."
They even went so far as to complete a further application of the tool: the Sterilizer.
"Now we have a concrete way to invite Milowina-san."
"I think Sally-sensei will be very happy with the Sterilizer too."
Satisfied with their work, Jin and Elsa decided to head to dinner.
"...I wasn't able to prepare it tonight either," Elsa murmured.
Instead, Mine had taken over the kitchen.
"Mother, thank you."
"It's quite alright. You seemed very busy with Jin-sama."
The menu consisted of barley porridge, omelets, fried whitefish, vegetable soup, and fruit salad.
"Mother's cooking really is the best."
Elsa was learning from her mother, yet she claimed she still couldn't replicate the same flavor.
"I suppose there really is no substitute for years of experience," Jin murmured.
Mine smiled and agreed. "Fufu, perhaps so."
"...I'll keep trying."
"Yes, you do that."
Mine brushed off her daughter's comment with the practiced ease of an elder. One could feel the deep bond between mother and daughter in their exchange.
Watching the two of them, Jin felt a slight twinge of envy—though he kept that thought strictly to himself.