"Elsa, I need to talk to you."

Erza answered Jin's words with a smile.

"...... I know. <

"Bingo."

Jin gave Erza a chuckle of admiration.

"I'd like to quickly examine the material. I can't help but wonder about this one."

"Yeah, I know. Have a nice trip.

Don't say good-bye. Come on, Elsa.

What?

"We don't know what's going to happen, so it's better to stay together."

Jin has seen many cases in anime and novels where people have been kidnapped by their girlfriends or family members because they were overconfident that they would be okay.

"Hmm, okay."

So Jin, together with Elsa and Reiko, was wrapped in magic and headed for <.

At the same time, with a piece of armor also arrived there.

<>, but thanks to their invisibility, they are undetected.

<, Jin silently flies to Horai Island through the warp gate in .

<

As usual, the old man's voice greets you.

"Please send my doppelganger and Erza's doppelganger in place of mine.

After giving instructions to the old man, Jin rushed to the workshop. Elsa and Reiko followed him.

He places the sample armor pieces on the workbench in the workshop, and finally begins to analyze them.

"So this is a piece of armor. It's so light. ......"

My first impression is that it is <.

"Really, it's light."

Erza also held the sample and was surprised at its lightness.

"Now, this metal... ......"

Jin's memory of modern Japan has one such example.

It was a metal that could be determined without .

"This is a foam metal.

"<>?"

Jin explains to Erza, who asks the question in a parroted tone.

"Yeah. I've only heard about it.

This is a material that was still in its infancy even in modern Japan, where Jin was from.

"The only thing I know about it is that you can use gas to make aluminum or titanium foam," he says.

He then looked at the sample in front of him intently.

"The material is probably titanium ...... light silver. And it has a lot of tiny holes in it. That's why it looks matte."

Jin told me honestly that he did not know how it was made.

"Even my brother Jin doesn't know?"

Erza looks surprised.

"Yes. But that doesn't mean we can't make something similar.

There are a few possible ways to make it, she added.

"Like what?"

Erza wants to know. Jin leaned back in his chair and began to explain his theory.

"First of all, the structure should have numerous small holes. In other words, we should make <> in the metal.

"I see."

"The problem is how to do it. The first idea is to create bubbles in the molten metal.

The molten state requires a very high temperature, but <> can be done at room temperature.

"......It is true."

"It is true, but ordinary air bubbles would not be able to form such fine bubbles. So, there is another possibility: ......"

Jin explained that bubbles could be created by magic.

"Then, depending on how you do it, you should be able to make very fine bubbles.

"Ah, I see. That's my brother Jin."

However, Jin shook his head.

"But this sample seems to have been made in a different way. ......"

Then, crossing his arms, Jin stared at the sample.

"But Brother Jin, isn't this one weak?"

Erza's voice reminded Jin of something he needed to do before thinking about the manufacturing method.

"Yes, indeed. That's why it broke into pieces like this.

"Then why did you make this thing?"

"Well, that's what it's for."

The advantages of foamed metals are that they are lighter and more heat resistant (some alloys), but Jin thinks that using them as armor is not acceptable.

"It would certainly absorb shock, though. ......"

That's all. Overall, it is not a good defense.

Then, the old man gives us some additional information.

, who was at the scene, that the wagon carrying the armor is also carrying barrels of some heavy liquid with it. The weight of the liquid ...... is estimated to be as heavy as liquid metal.

"What!"

Jin gets up from his chair at the new information.

Then he sits down again, but this time with a sly grin on his face.

"Brother Jin?　What's wrong?"

"...... I think I know how to use this from the information you just gave me."

"What?"

Jin slowly explains to Erza, who tilts her head, as if admonishing her.

"Foam metal and liquid metal. Is there anything you notice about this combination?"

"...... Uh, seepage?"

"Yes."

Jin nodded his head.

"Probably, the armor made of this foam metal will show its true performance only when it is soaked with liquid metal.

"What do you mean by 'original performance'?"

Jin smiled at the question.

"That's exactly what we don't know because we don't have the liquid metal. But I have two guesses.

"Can you tell me?"

"Sure. ...... First, we need to strengthen the armor.

Yeah, I can see that.

I'm sure you do.

Foam ...... and metal are the two things everyone associates with it.

"I think it would dramatically increase the strength."

At least, that is the reason why Jin had no idea what material the armor worn by No.41, <> was made of.

"It is neither alloy nor plating. < state, so its appearance is unique."

It is not surprising that it was difficult to tell from a distance.

"But, perhaps," he said, "another guess might be in order."

"And what is that?"

"That's the one thing I've been chasing since before this..."

Jin cut off the conversation and continued.

"It is the use of the <>.