Erza, Saki, and Reinhardt are consulting with Jin, who has asked them to come up with a .

"The original idea is a mithril shield," says Reinhardt.

Reinhardt said.

"But then, we can't wear it all the time, can we?

Saki pointed out the problem.

"Then why don't we make helmets out of mithril woven cloth or something like chain mail?

Elsa offers her opinion.

"Yes, that would be a good place to start."

Reinhardt agrees and we start with an experiment.

"Would mithril be a good material?"

"Mithril would be a good material, wouldn't it? "Yes, considering its practicality, I suppose so.

There is also a material called < shell, but it is not common.

If it is to be used as equipment for the <>, it must be a common material for practical use.

"However, I think it would be good to experiment with it as a sample for comparison."

Erza said.

"I agree. <.

And so the experiment began.

"First of all, <>, can Elsa use it?

"I don't think so, I've never practiced it."

"I don't think so."

"But I've used it before with a hypno-magic."

I used it on Najaz Khan.

"But are you going to use someone else as a test subject?"

"...... Saki's right."

The three of them are wondering what to do.

And then...

"Brother Rai, can't you make a magical tool that glows when it receives such magic?"

Erza said with an idea.

"I see. That might be a good idea."

Reinhardt replied and immediately started to make a magical tool.

"...... but we can't use > if there is some kind of equivalent magic ......."

"Oh, then, how about <>, the magic of release?"

"Yes, that might be a good idea."

Erza has developed a magic for disarming brainwashing. If it doesn't work, it seems that brainwashing magic won't work either. We decided to proceed with the experiment based on this assumption.

A wooden mannequin head is made, and a magic tool is implanted in it. There are holes in the eyes, through which light leaks when brainwashing magic is detected. It's a little creepy.

After confirming that the eyes light up with Erza's <>, we start the experiment.

"Let's start with Mithril's helmet.

A full face, one millimeter thick. It looks a bit like a knight's helmet, but basically it looks like a full-face motorcycle helmet with a mithril shield.

The eyes have slit holes in them so that the wearer can see out.

"Okay, I'll give it a try. ......<>"

"It doesn't glow."

"It doesn't glow. So this is shielding well enough.

"Next, a helmet of the same material and shape with half the thickness.

A full face helmet with a thickness of 0.5 mm. It also shielded well.

"It works better than I thought."

"Well, that's a nice miscalculation."

Then, the next question is what shape to make.

"I'd like to try it in the direction of what would happen if we made it into a hat.

"Oh, you want to reduce the area that covers the head.

"That kind of thing."

And the result is.

"No hats?"

"The back of the head has to be protected."

I understood that.

But a jet helmet for motorcycles works well. It seems that covering the back of the head is the key.

"What if we make it thinner?

"What if we make it even thinner?" "If we make it 0.3mm thick, the effect will be weaker.

"Kuhu, I think 0.5mm is the maximum thickness with some leeway.

"Hmm, that's a good conclusion.

"Next, how about making a mesh?"

A mesh made of mithril's ultra-fine wire is processed into a jet-helmet shape. It looks a bit like a flying cap.

"Oh, this is surprisingly good."

The shield was effective.

Let's make it coarser and coarser.

"Hmm."

At first, the weave was so dense that it was almost impermeable, but then the weave was gradually made coarser.

As a result, the first millimeter was fine, but the second millimeter was not.

"Kuhu, then a hat made of 1mm mesh should be able to protect it, right?"

"Hmm. The only thing left is the design.

"So that's what you mean. We can make it so it doesn't look like protective gear, or we can make it look like an under-helmet cap."

"What's that, Rai?"

Elsa asked at the unfamiliar word.

"What is it?　<?"

"Yes."

"Erza would not have known about it, since she would not have had anything to do with full-body armor. <

"Hmph, underwear for the head, I guess..."

"I don't know if that's the right way to put it, but ...... well, it's not wrong."

Even in modern Japan, there are people who wear under helmet caps under their motorcycle helmets.

Especially in summer, the head also sweats, so there are caps made of sweat-absorbent materials or with excellent ventilation properties to prevent the inside of the helmet from getting stuffy and smelly.

In addition, helmets for construction sites are sometimes made of non-woven cotton cloth and put on in advance.

Elsa began to think about a design that would be conscious of such products.

At the same time, Reinhardt and Saki decided to make a comparison experiment with the shell of an "ancient dragon," and produced a normal hat-type hat, not a flying cap.

"Even though it's so thin, it's probably effective.

I guess. ......Erza, I'm sorry to interrupt your work, but I need you to <>."

"Yes."

And as expected, the hat made from the shell of the ancient dragon prevented the effect of <> in the comparison experiment.

"Probably because of the strong network of free magic element (ether)".

"That's why it is so effective even though it doesn't cover the back of the head."

"Kuhu, I like hats for family use."

Thus, the experiment of the three ended with the result that the shell of the <> had a great effect.