What Are You Doing, Sis? (15)
What Are You Doing, Sis? (15)
"What is this...! Why is it so complicated!!"
Frey recoiled the moment she saw the blueprint.
"Last time I made that donut-shaped thing for you, I thought I was going to die—it wrecked me for days!"
"So?"
"What do you mean, 'so'?! This looks even harder to make than that! Transmuting this without mana depletion would take at least a month!"
Frey had already suffered through mana depletion while building the tokamak. She had managed to finish it somehow, a mana cigarette clamped between her teeth, but then she had handed it over to Kasha... Either way, I owed her an apology.
I had no desire to get so buried in the task at hand that I turned into Professor Haspelt. This project needed to benefit Frey as well as me.
"It's fine. We can take our time building this one."
"...Really?"
"Really."
Frey was a cheerful, bouncy friend. Put another way, she was distractible in certain respects.
Of course, being admitted to Tillet at all was proof she was a gifted student with exceptional focus. But after watching Frey for more than half a year, I knew she showed no interest in work she disliked.
She ought to be that kind of person. Yet even now, while she was grumbling and complaining, she hadn't said a word about quitting.
"Still, if I can finish this, I'll be able to erase at least a little of the prejudice that says the Fox Beastmen are all fools.... Hehe."
That was because, like Rote, I had told Frey the nuclear weapons production plan. The plan to fabricate the world's most powerful bomb, annihilate the magic beasts, and restore the world to its proper order.
I wouldn't be around by then, but I hoped this little one would live happily in the world that remained.
Frey had entered Tillet under a concealed identity for the sake of her tribe's revival. She was a friend who would not hesitate to risk her own life if it meant reviving the Fox Beastmen Tribe to which she belonged.
The enmity between humans and beastmen ran deep. Records even showed that before the Demon King's army appeared, beastmen had been called monsters. Well, that tracked. Humans were the sort to discriminate over something as trivial as a different eye color.
No, maybe it wasn't just humans. Whether beastman or elf, disliking other species seemed to be a racial instinct.
They persecuted one another, hated one another. Now that magic beasts had devoured a third of the continent, the sentiment had thinned considerably, but those who wanted to discriminate still discriminated.
And in that climate, Frey did not treat humans with hostility. She did not fear them, and she did not look down on them.
She would create a world of equality that transcended racial difference. That was the answer Frey had written when Professor Herlein asked them to describe their future plans.
"You, me, and Rote—the three of us are going to complete this! If this becomes the key to winning the war against the magic beasts, then it's good for you, good for Rote, and good for me! People might even talk about it for generations! They'd say our tribe was actually kind and great!"
"Right. So how about we try building this thing?"
"Ugh... This is why you sound like an exploitative professor."
"That's harsh."
I gave a wry smile and held out a mug of coffee to Frey.
"It's cheap instant mix, but nothing beats it for cost-effectiveness."
"I actually like this better! I don't get why anyone drinks black coffee."
We didn't have the leisure to savor the aroma, either. The point was purely caffeine intake, so it had to go down like juice.
After rinsing my mouth with coffee, I handed Frey a cigarette. It wasn't a "Goldenstein." Just an ordinary variety of mana cigarette extracted from common leaf you could find in any market.
Savoring the bitter-astringent taste of the herb, we looked back and forth between the blueprint and the magic stones.
"The iron or titanium for the fuselage came from the museum, so we shouldn't run short."
"Actually, if we factor in density reconstruction, what we brought might not be enough."
"Density reconstruction?"
"We want to make it as hard as possible, right? Look at this. The thing's nearly five meters tall, and if we need to maintain that hardness, we'll have to grind the material fine and compress it. Naturally, that takes a lot of mana and a lot of iron."
"Now that you mention it, it does look a little short..."
After discussing it further with Frey, I decided we would start by building just the skeleton.
Unlike the internal structure that would carry the explosive payload, the outer shell was comparatively easy to produce. The mana consumption was genuinely lower, too.
At least I had a friend who was well-versed in transmutation to act as a blast furnace for me. If this weren't an arcanepunk world, I would've had to curse my way through every step of the process. Actually, before that, I never would've dreamed of building a nuclear weapon by myself.
"Alright. At this rate, we should be able to put up the frame today."
"Want to knock out the internal structure while we're at it?"
"No?"
I'd meant it as a joke, but when I saw Frey's face stiffen, I dropped it.
The time-consuming part wasn't the outside; it was the inside. Multiple magic stones had to be installed, and like a scroll, numerous circuits had to be linked. Then load the explosives, and this, and that...
Come to think of it, the method for manufacturing an atomic bomb was classified on Earth. But how I knew such a thing wasn't an issue.
Aether had been alive since at least the era when the Demon King first raised his army. And since the Demon King had been sealed a thousand years ago... Hm. Let's not talk about it.
'I' had spent all that time doing nothing but eating and research. It wasn't strange that I knew these things.
"Well, keep at it. Don't get distracted."
"I won't?"
I left Frey behind as she wove a transmutation formula without even a transmutation circle, and returned to where Rote was. Rote had her head in her hands, deep in thought about something.
"Oh, you're back? This is really hard..."
What Rote was looking at was the incomplete White Night scroll.
The goal wasn't to complete White Night itself. That would take considerable time even if I borrowed from Aether's knowledge.
What was possible, however, was interpreting the sections already completed and teaching them to Rote.
"Help me with this part."
"Let's see..."
I sat down in the chair opposite her and examined the output section of White Night.
At the scroll's junction, a total of 2n² tangent lines existed. Here, n was a natural number: 1, 2, 3... Unlike an ordinary scroll, White Night described its junctions in the form of an indefinite constant. This corresponded to the number of independent variables an n-dimensional complex square matrix could possess.
"Um... Aether?"
I opened my mouth after a moment of thought.
"Listen carefully, Rote. The world we live in can be described with coordinates. That's middle-school material, so no problem, right?"
Rote nodded. I continued.
"We can express these coordinates as vectors. In linear algebra, a vector is represented as a tuple consisting of a row or a column. And we can arbitrarily multiply it on the left by a matrix of matching dimensions. What's this process called?"
"A transformation."
"Correct. It's called that because a coordinate multiplied by a matrix is 'transformed' into another coordinate. So let me ask a question. Suppose we have two coordinates. We can define the distance between them, yes?"
Again, Rote bobbed her head. She understood this as well.
"Now here's another question. Could the distance between two points be independent of the coordinate transformation?"
"Generally, wouldn't it change?"
"Probably. But what if I impose that condition as a requirement?"
"Then the matrix would have some constraints."
"Oh... Correct."
Even I thought Rote was a genius. To follow this far without difficulty.
A first-year academy student wouldn't have properly learned linear algebra yet. If you taught her one thing, she figured out two. This was partly the result of the tutoring I'd given her over the past six months, but it was also the result of the knowledge Rote had accumulated by studying on her own.
"So we can think of the set containing all those matrices, right?"
"Yeah."
"Let's derive that for a moment."
I wrote down the conditions for a matrix with that property, proved a few characteristics, and showed the concrete form. Rote followed my explanation without a single snag.
"Now look at the scroll again."
"Oh... Wait."
Rote glanced back and forth between the equations I had scribbled and the scroll, then let out an admiring sigh as if she had figured something out.
"The scroll turned what's in here into geometry!"
"Exactly."
"So that's why you borrowed a whole stack of math books and related papers...!"
Watching Rote get excited, I let the corners of my mouth curl up. It was like looking at my past self.
During the transition from undergrad to my first year of the integrated master's-PhD program, I had studied an immense amount of mathematics. In the process, I'd dipped my toes into theoretical physics and nearly drowned. Among everything I'd learned then, the experience I'd just taught Rote was one of the meaningful ones.
At the time, I'd been taking a graduate-level mathematical physics course, and the professor teaching it had demonstrated how to derive special relativity using pure mathematics without a single ounce of physical intuition. My jaw had dropped the first time I saw that.
Right now, Rote looked exactly the same. Before long, I'd probably be able to show her that electromagnetism could also be derived through mathematics alone.
Reaching that point would require a lot of work. To get all the way to U(1) symmetry, I'd need to lecture nonstop for at least ten hours...
"This is amazing! So, can I explain this section similarly? Or would it need a different transformation?"
...Probably would have to.
Rote stared at me with sparkling eyes. I'd seen that look somewhere many times before. Right—the look in her eyes when we first met at the bar.
Live long enough, and you occasionally meet someone whose curiosity overpowers appetite, lust, even the need for sleep. Rote was exactly that type. Her stamina, which she'd never neglected because of her combat magic training, was top-class even among our classmates.
"This is easier than I thought since you're helping! At this rate, I think I can understand it all by the end of today."
"No... I'd need to split the explanations over at least a week just for the output section..."
"Would about ten hours do it? Please. Let's not drag it out—let's just finish it all today!"
And so we blew an entire day. Though on the way out, I felt a little better thanks to Frey, who had finished building the large and imposing bomb frame.
Anyway... that was how my sweet Saturday went up in smoke.
I rubbed my dark-circle-ridden eyes and trudged toward the dormitory. Then I stopped, struck by the feeling that I'd forgotten something.
Wait.
"Oh, right. Vermel."