Having been tasked by Jin with developing countermeasures against Brainwashing Magic, Elsa, Saki, and Reinhard were conferring together.
"The basic idea is to create a barrier using mithril," Reinhard said.
"True, but you can't exactly keep wearing a solid helmet all the time, can you?" Saki pointed out the issue.
"Then what if we made a helmet out of cloth woven with mithril, or something like chainmail?" Elsa suggested.
"Yeah, that's probably the right track."
Reinhard agreed, and they decided to start with some experiments.
"Would mithril be the best material?"
"Kufu, yeah. Considering practical use, that's what it comes down to."
There was also the option of using shed skin from an Ancient Dragon, but that wasn't an everyday material.
If this was going to be standard equipment for the World Security Guard, it wouldn't be practical unless it was made from accessible resources.
"Though, I think it's good to experiment with it as a comparison sample," Elsa said.
"Kufu, true. If we're making it for Jin Family use, we have plenty of stock anyway."
With that decided, the experiments began.
"First off, regarding Hypno... can you use it, Elsa?"
"I've never practiced it, so I don't think I can."
"Figures."
"Though, what about the Hypno magi-device we used before?"
She meant the one used on Najas Kahn.
"Wait, do you intend to use someone as a guinea pig?"
"...Saki has a point."
"Hmm, what should we do?" The three of them pondered the dilemma.
And then:
"Rai-nii, couldn't you make a magi-device that lights up when it receives that kind of magic?" Elsa voiced an idea.
"I see. That might work."
Reinhard answered and immediately began crafting the magi-device.
"...Though if we can't use Hypno, that's still an issue... If only there were some equivalent magic..."
"Ah, in that case, what about the cancellation magic, Wecken?"
"Yeah, that might do the trick."
Wecken was the brainwashing cancellation magic Elsa had developed. If this had no effect, it stood to reason that brainwashing-type magic wouldn't work either. They decided to proceed under that premise.
They fashioned a mannequin-like head out of wood and embedded the magi-device inside. Holes were drilled into the eye sockets so that light would shine through when brainwashing magic was detected. It looked a bit eerie, however.
After confirming that the eyes properly lit up when exposed to Elsa's Wecken, the testing began in earnest.
"First up is the mithril helmet."
It was a full-face helmet with a thickness of one millimeter. It bore some resemblance to a knight's helm, but fundamentally, it was shaped like a motorcycle helmet where even the face shield was made of mithril.
Slit-like openings were cut into the eye area to allow the wearer to see out.
"All right, let's try it....Wecken."
"It didn't light up."
"Nice. So that means it provides an adequate barrier."
"Next is a helmet made of the same material and shape, but with half the thickness."
This was a full-face helmet with a thickness of 0.5 millimeters. This, too, formed an effective barrier.
"It works better than I expected."
"Kufu, a pleasant surprise."
With that established, the next question was what shape to test.
"I'd also like to see what happens if we make it a cap."
"Ah, reducing the surface area covering the head, right?"
"Exactly."
And as for the results:
"A cap is no good, huh."
"Looks like it doesn't work unless the back of the head is protected."
That was what they discovered.
However, an open-face helmet style was effective. Covering the back of the head seemed to be the crucial factor after all.
"What if we make this shape even thinner?"
When reduced to a thickness of 0.3 millimeters, the effect weakened.
"Kufu, leaving a bit of a safety margin, 0.5 millimeters is the limit."
"Mm, that seems like a sound conclusion."
"Next, let's see if we can make it out of mesh."
They processed a mesh made of ultra-fine mithril wire into an open-face helmet shape. It ended up looking somewhat like an aviator cap.
"Oh, this is surprisingly good."
This successfully produced a barrier effect.
"Let's gradually make the weave coarser."
"Mm."
Starting from a weave so dense it was barely translucent, they loosened it step by step.
As a result, a one-millimeter mesh held up, but a two-millimeter mesh failed.
"Kufu, so that means a cap made of a one-millimeter mesh should be able to block it."
"Mm. The rest comes down to design."
"I see. Making it look like ordinary headwear is fine, and designing it like an under-helmet cap would work well too."
"Rai-nii, what's that?"
Elsa asked about the unfamiliar term.
"Hm? You mean an under-helmet cap?"
"Yes."
"I suppose you wouldn't know since you've never had to wear full-body armor, Elsa. An under-helmet cap is a cap you wear underneath a helmet."
"Kufu, like underwear for your head, I take it?"
"I'm not sure about that phrasing... but well, you're not wrong."
Even in modern Japan, people wore under-helmet caps beneath motorcycle helmets.
In the summer especially, since the head gets sweaty, there were varieties made from sweat-absorbent materials or high-breathability fabrics to keep the helmet from becoming stuffy and foul-smelling.
Additionally, workers on construction sites often put on a cotton non-woven fabric cap before donning a hard hat.
Elsa began brainstorming designs with the intention of creating something inspired by such products.
At the same time, Reinhard and Saki, intending to run a comparative experiment with shed skin from an Ancient Dragon, crafted an ordinary cap rather than an aviator-style one.
"Even this thin, it'll probably do the job."
"Most likely....Elsa, sorry to interrupt while you're crafting, but could you hit it with a Wecken?"
"Mm."
In the comparative test that followed, just as expected, the cap made of shed skin from an Ancient Dragon splendidly fended off the effects of Wecken.
"Presumably because its free ether network is so robust."
"So that's why it works so well even without covering the back of the head."
"Kufu, a cap will be just fine for Jin Family use, then."
Thus, having proven that the shed skin of an Ancient Dragon offered exceptional protection, the trio brought their experiments to a successful close.