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“You can have this as a memento of this day. It can replace the one that was broken in the fight.”

Sayama took the watch and put it on. He noticed Ooshiro was already wearing an identical one.

After Ooshiro saw Sayama had finished strapping the watch on his left wrist, he opened the door behind him.

The metal door opened inward.

Beyond the now empty space was a passageway with closed shutters on either side.

“This passageway runs through the center of UCAT. But right now…”

Ooshiro entered the passageway. Sayama stood before the door alongside Shinjou before setting foot inside.

Once he did, he heard a voice.

—Your feet are on the ground.

“?”

Sayama tilted his head in puzzlement. He felt as if he had heard a few other voices after that first one, but he had been unable to make out the others. He only recalled that he had heard a voice.

But Sayama recognized this voice.

It was the same voice that he had heard upon entering the forest that evening. However, he did not understand what it meant.

…What does it mean that I heard this voice?

As soon as he thought that, he felt a small vibration on his left arm.

It came from the wristwatch he had been given. He felt as if it were vibrating.

He looked down and for just an instant saw something like red writing scroll across the face of the watch.

That writing disappeared before he could read it.

“Is this a trick watch?”

It was currently ten till nine, so this was not indicating the top of the hour. Also, Sayama could not determine what that scrolling writing had been.

As question after question appeared in his mind, Sayama suddenly reached behind him.

However, he found no invisible wall. And the second hand of the watch was still moving when he looked back at it.

[...]

What lay before Sayama’s eyes was a world with no distinction between up and down.

Both the office floor to the right and the large hangar to the left had desks, equipment, and working people on the floor. However, there was more than that.

“They are on the ceiling and walls too…”

People and equipment were there. Work was being done.

To both the left and right, the ceiling was being used as another floor.

As if it was a mirror image of the floor, desks were lined up on the ceiling of the office. The occasional decorative plant could even be seen.

The only thing that differentiated either one from a normal office was that the walkway down the center was made of covered lights which illuminated the other. The ceiling lit the floor and the floor lit the ceiling.

On the ceiling, people wearing office clothes stared at screens on the desks and typed on keyboards, walked here and there with paperwork in hand, or pushed carts full of documents.

Sayama observed those people on the ceiling.

But despite standing upside down on the ceiling, their hair did not stand on end and their feet were not attached to the floor on the ceiling.

Suddenly, a woman carrying documents on the ceiling accidentally bumped her hip against the corner of a desk.

With a look of surprise, several papers scattered through the air. They spread out and “fell” to the ceiling.

She frantically gathered them and a man on the floor directly below her called out to ask if she was okay.

Sayama saw all this. 

He remained silent as Ooshiro approached one of the windows to the office floor and opened it. Everyone on both the floor and ceiling turned toward him.

“Ooshiro-san!” cried a voice.

He nodded in response and said, “Are you doing well?”

“Testament!”

Hearing that, Ooshiro moved away from the window. As the workers all returned to their work, Sayama finally opened his mouth to speak.

“What is this?”

“It is exactly what it looks like. …Now, look to your left.”

Sayama ignored Ooshiro’s thumbs up and looked to the left as he had been instructed.

That was the three-story maintenance hangar. The passageway he stood in was at the second story portion, so the hangar spread out for one story both above and below.

The vast floor was surrounded in concrete. In there, people were working on not just the ceiling, but the walls as well. All four walls, the floor, and the ceiling were lit by large lights protected by bars at the corners of the surfaces and along the walkways.

A large object was currently located in the center of the ceiling. It was an armor-like humanoid machine about eight meters tall.

Of all things, it was lightly raising both its arms, standing tiptoed on its right leg, and rotating.

Ooshiro opened the window and spoke over the mechanical noises coming from the hangar.

“Oh, would you look at that. A balancer test.”

The humanoid machine stopped after fifteen revolutions and went down on one knee as if dizzy. The surrounding workers gathered around it and peered into the area analogous to a face.

This sight brought a wordless thought to Sayama’s mind.

It was strange.

He nodded, now convinced, and suddenly opened the window in front of him.

He heard loud mechanical noises, smelled the burning scent of welding, and saw bright lights higher up.

He had seen a small shadow on the upper edge of the window he had opened. A closer look showed it was a wrench dropped on the floor on the reverse side. Most of the grip was sticking out onto the window, so Sayama could only think it was sticking to the wall by ignoring gravity.

“What is going on?”

Sayama placed a hand on the window frame, placed a foot on it as well, and prepared to jump out to the other side. But then someone grabbed his belt from behind.

“Y-you can’t do that, Sayama-kun! If you fall, you’ll die!”

Sayama stuck his head out the window and looked around.

Despite sticking his head out along a wall, people and equipment were standing straight on it and working.

After watching those workers standing and walking along the wall, he spoke to Shinjou behind him.

“Sorry, but please let me go.”

“Y-you can’t rush this!”

“I have made up my mind. I must go to the other side!”

“You can’t! It’s too soon! Please rethink this!”

“Do you think this is a training ground for jumping to your death? This may only be the second floor, but you might be injured if you fell.”

Hearing Ooshiro say that, a question entered Sayama’s mind. He stopped moving and asked it.

“Why do you think I will fall? They are standing on the other side of this wall, so-…”

He trailed off.

A giant trailer drove along the vertical floor from the left.

It was driving relatively quickly for the small area.

The instant of rumbling, wind, and shadow caused Sayama to duck back a bit as it passed by overhead.

The vibration caused the wrench sitting on the edge of the window to shake and drop down toward him. As he saw the wrench graze his face and fall behind him, Sayama frantically ducked back into the window.

He climbed down from the window frame and onto the passageway floor as wind from the trailer blew in through the window. The wind stank of exhaust, but it also contained a slight citrusy aroma.

Sayama took a breath. He then looked through the window at the humanoid machine standing up on wobbly legs.

“But…” He recalled the school newspaper attached to the wall in the school building. “I thought those things could not walk properly? Is your actual technology at this level?”

“Do you think we purposefully send out weakened mechs to be destroyed so no one will know what level of technology IAI has? Why would we need to put on such a performance? Mikoto-kun, the machine used in the article your school published was a god of war with the same design as this one. However, it was piloted remotely.”

“That machine was unable to walk without destroying itself, so how can this one move like this? Has the durability of the metal or gravity been altered?”

“I am glad the thought occurred to you. …What if we could control gravity?”

Sayama frowned. It sounded ridiculous, but a similar phenomenon could be seen before him. People were standing and working on the ceiling and walls. He looked at them and himself, but then he realized something that did not add up.

“Wait… You said I would fall when I placed my foot on the window frame before. If you could control gravity, I would stand on the wall instead of falling when I exited the window.”

“What if we were merely mistaken?”

“Then tell me this: what is that?”

Sayama pointed at the window to the office floor. A single object sat on the window directly opposite the one to the hangar Sayama had opened.

It was a wrench.

It sat on the window as if that window were the floor.

Sayama approached the window and touched it. A few people working beyond the window noticed him, but Sayama ignored them and spoke.

“We feel no attraction from this window. But this wrench does. …Is gravity being individually controlled for this single wrench? Does this continue until it leaves the effective range?”

Sayama approached the wrench and touched it with his hand.

The wrench immediately fell to the floor. It had been falling toward the window before, but the direction of its fall had changed. And the change had occurred as soon as Sayama touched it.

He looked down at the wrench on the floor.

“This is not gravitational control.”

He thought about why Shinjou had stopped him from leaving the window and about what Ooshiro had told him. And then he thought about the meaning of the words he heard upon entering the passageway.

“It said my feet are on the ground.”

As he spoke, Sayama raised his left foot toward the office floor window before him. He placed the sole of his shoe on the window.

He took a breath as he hesitated slightly.

And then he pushed off the ground with this right foot.

As he brought his right foot up toward his left foot, his body fell perpendicular to the window.

If he did not do anything, the back of his head would crash into the floor.

However…

“So this is how it works.”

Sayama placed his right foot on the window. He placed it right next to the left foot already on the office floor window.

He stood.

He looked around. Shinjou and Ooshiro stood on the wall to his left which was actually the floor.

Sayama was currently standing on the window. 

[...]

Every sense in his body was telling him the window to the office floor below his feet was the ground. His left arm that hurt when he moved it was naturally hanging down toward the window. He used his right hand to touch the hem of his clothes and it was hanging down toward his feet as well.

“What is going on?” asked Sayama. “I do not know if you have the technology to control gravity or not, but this is strange. Why are only the things I am touching viewing the direction of my feet as down?”

He looked up toward the hangar above his head. Diagonal slopes had been built in places to connect the walls and ceiling. The area was arranged so that large equipment and that trailer could freely move about.

Sayama looked back down. Shinjou’s gaze met his from where she stood perpendicular to him.

“Shinjou-kun, excuse me, but I would like to try something.”

“Eh?” said Shinjou as she took a step toward him.

Sayama nodded and took her hand.

However, Shinjou remained standing on what was the wall to Sayama.

“So you do not fall this way.”

“D-don’t try such dangerous things.”

“I was prepared to catch you. Do not worry.”

“I’m not sure if I can…”

Ooshiro gave a bitter smile and said, “Unless you jump into the air, what is set as the ground will be constantly updated for you. In other words, the world always exists below your feet in this space. The concept related to gravitational pull has been altered.”

“I see,” said Sayama as he let go of Shinjou’s hand. He looked toward Ooshiro and continued, “What exactly is this power?”

“Let me ask you something instead, Mikoto-kun. How do you think you could explain this power? What if you met with academics and intellectuals from around the world and asked them what power can alter the world so conveniently?”

“They would say it is a trick.”

“Exactly. However, this is the truth. Now, another question. …What basis would they use for determining this is a trick?”

“That is obvious. This breaks the laws of physics.”

“Yes, yes. Indeed it does. Light is bent by gravity, but with this power, light only bends according to the direction set as the ground for it. Even if the real ground is in a different direction. But Mikoto-kun, when you talk about the laws of physics, what world’s physical laws do you speak of?”

“This world’s physical laws.”

“Then let me ask you something else. If alternate worlds did exist, on what basis would we determine they are different from our own? The terrain? The atmosphere? The life forms? Or perhaps the culture?”

With that question, Sayama realized the answer to it all.

He finally said, “Is this what you want to say? There was a world with physical laws fundamentally different from our own. And this power we are seeing follows that world’s laws!”

“Precisely. This world’s physical laws cannot be applied to other worlds. A world with different physical laws will naturally overturn the very basics of the physical laws we know.”

“But there have to be certain absolutes, right? Like the motion of light.”

“No, no. Even that is based on this world’s physical laws. When light is emitted, it spreads and continues on. But why does it do that? Why can’t there be light that does not do that?”

“That is…”

“That is simply what light is in this world, right? But,” Ooshiro took a step forward so their gazes would match perpendicularly, “what if light being that way was actually quite rare?”

“…”

“We only know how things work in this world. We assume the workings of this world are absolute. But what if there were a great number of other worlds and it turned out the rules of this world are great exceptions compared to the other worlds?”

“But we do not know of any other worlds, so we can only assume they would be the same as us.”

A bitter smile appeared on Ooshiro’s lips when he heard that response.

“True,” the old man said. “But another world is another world. They are fundamentally different. What we think is simply ‘how things are’ and what the other worlds think is simply ‘how things are’ are fundamentally different.”

“Are you saying,” Sayama looked down at his feet, “there is a world where this is how gravity works?”

Ooshiro nodded, walked over to the opposite window, and stood on it. He looked straight up toward Sayama.

“The ten other worlds and this world are perceived as individual gears and so we refer to them as such. 1st-Gear through 10th-Gear all had their own unique characteristics. And do you know what we called this power of ‘how things are’?” Without waiting for an answer, Ooshiro said, “Concepts. We called them concepts! They are a power that can control even the laws of physics. They are the ultimate reason behind everything. That is what concepts are!”


Sayama gulped at Ooshiro’s words and looked down toward his feet and then around his entire surroundings.

“In other words, the concept of ‘your feet are on the ground’ is being used to make efficient use of this small underground space? …Was that voice I heard upon entering the concept?”

“That was a concept text. It is made by gathering inferior reproductions of an extracted concept. Each individual concept is very weak, but it can be heard as a voice once it reaches the level of a concept text. This space also has several weaker concepts added on as well, but they cannot be heard as a voice.” He continued. “When an out of phase space has concepts added to it, it is known as a concept space. We think of a concept’s identity as a variable fixed-period vibration wave that we call a string vibration.”

“This just got a lot more complicated. A string vibration, you say?”

Sayama thought.

Ooshiro had said an alternate world was a world with different concepts. In that case…

“So alternate worlds are worlds with different string vibration frequencies?”

“Yes. And everything in any of the worlds has a string vibration for their world and a string vibration for the object itself. The one for the world we call the parent string vibration and the one for the individual we call the child string vibration.”

Sayama nodded and said, “So is it like a numerator and denominator? The denominator tells you what Gear they belong to and the numerator tells you what the individual is.”

“Yes. If the numerator differs, it is a different individual. If the denominator differs, it may be the same existence but from a different world. These alternate worlds are not parallel. They exist in multiple phases atop each other. According to the records, a ‘gate’ that alters one’s parent string vibration is needed to move to and from different Gears.”

Sayama then recalled the invisible wall surrounding the forest.

“This evening…was that a space that’s parent string vibration had been completely altered?”

“Not quite. If its parent string vibration had been completely altered, that space would have completely disappeared from this world. But,” Ooshiro raised his index finger, “what if only a portion of its parent string vibration was altered?”

“In that case, would the altered objects world split into two existences? The real one and the alternate world one would exist on top of each other at the same time. …And that means the objects would not disappear from reality.”

He remembered the stone he had picked up in the forest. He remembered how it had left a pale shadow behind.

“So two versions of that forest existed on top of each other? I am guessing a smaller portion had the alternate world string vibration than the reality string vibration. Could I not leave because of the difference in vibration density?”

“Correct. How very wise of you. That is what we call a concept space. It is only a pseudo-alternate world created by borrowing a portion of an area’s string vibration. Since it is still connected to the real world, it is easier to create and return to normal.” As he spoke, Ooshiro showed off the watch on his left arm. “I gave you one of these before we entered this concept space. These watches are known as string watches. They detect the wall of a concept space and alter the wearer’s parent string vibration accordingly. They are a small version of the ‘gates’ I mentioned earlier.”

“But how did I enter the concept space in the forest without one?”

“Someone secretly read your child string vibration. When the forest was turned into a concept space, your string vibration was registered so you would be allowed in. That is one thing that can be done when creating a concept space. And I apologize,” said Ooshiro as he looked toward Sayama’s left arm. “It seems we rushed things. We only wanted to let you experience it for yourself, but you ended up getting injured due to the inexperience of our units.”