Lu was groaning over her meal.
It was because her Teleportation Gate Research wasn't going well.
For the past few days, a deep crease had remained fixed between her eyebrows.
It was disheartening to see her look so stressed while eating the chestnut rice I’d worked hard to prepare.
However, there was nothing I could do to help.
I didn't understand the first thing about Lu's research.
Concepts like Magic Power Flow, the interference of spirits, or the alignment of the stars were bars set far too high for me to clear.
But even so, could I really just sit by and watch my wife suffer?
As her husband, surely there was something I could do.
After we finished eating, I spoke to her.
"Lu. Why don't you try explaining the parts you're stuck on to me?"
"Eh? But..."
"I don't expect to understand the specifics or find a solution myself. But sometimes just explaining things to another person helps you organize your thoughts, right?"
That was all I could really do—be a listener.
"Well, you see, these two numerical values seem to be based on the sun, but their rate of change varies depending on where the gate is set up. I just can't figure out why."
"How does it vary?"
"Um, to put it simply... In the first location, the base value is ten, and it increases by one at a time. But in the second location, the base is eleven, and it increases by two."
"I see."
"In the third location, the base is eleven and it increases by three... and in the fourth, the base is back to ten but it increases by two. There are two values like that that just make no sense. Oh, and the actual numbers are much larger and more precise, obviously. I'm just using ones and twos to make it easier to explain."
"Thanks. Two values based on the sun that change depending on the location... If I were to think of them as factors, the obvious candidates would be rotation and revolution."
"……Eh?"
"You know, rotation and revolution."
"What are those?"
"Huh?"
...Ah. This was a fantasy world. It was entirely possible that the sun moved and the land was flat. After all, this night sky had two moons.
"Sorry, forget I said anything."
"No. Tell me. In detail."
There was a frightening glint in Lu's eyes.
I proceeded to teach Lu about rotation and revolution. Rotation is the movement of the Earth spinning on its axis. Revolution is the movement of the Earth orbiting around the sun. I kept the explanation as simple as possible. I explained that the change in seasons comes from the tilt of the rotation relative to the sun and the slightly off-center elliptical orbit the planet takes.
"I want to call that nonsense, but it explains so many things that have been baffling me until now."
That was a relief. It seemed the same Heliocentrism from my previous world applied here as well. Which meant the world was a sphere.
However...
"Is it not common knowledge that the world is a sphere?"
"There were eras where people suggested it, but no one could ever prove it... The current established theory is that the world has a gentle hemispherical shape."
...
As a representative of the dragons who fly through the great sky, I decided to ask Hakuren.
"The world is obviously a sphere, isn't it?"
Lu collapsed onto her knees.
"By the way, I've already been teaching that to the children. Was that a problem?"
It wasn't a problem, no. But it certainly felt like a finishing blow for Lu.
Lu, are you okay? Can you get up? ...Apparently not. She decided to just go straight to sleep right there. Fair enough.
From the next day onward, Lu stopped groaning during meals, but she started to get a distant look in her eyes.
"Maybe I should start attending Hakuren's classes too."
I didn't know how to respond to that, so I simply ate my meal in silence.
I'm sorry, Lu. I’m useless here.
It took about ten days for Lu to finally get back to her usual self.