The man called Librio—or rather, the book—rose from the desk and flew around Nemusia.

It didn't flap its pages like a butterfly, but seemed to float using some mysterious power.

Nemusia also used magic distinct from skills, so I guess it's a world where such power exists.

"It is strange. Even though your appearance looks nothing like Her Majesty from any angle, your way of speaking is exactly hers."

"There are circumstances behind this."

"No, I am not doubting that you are Her Majesty. His Highness the Prince also said something to that effect."

"My older brother did!?"

She instinctively grabbed Librio.

And gripped him so tightly he looked ready to tear.

"Your Majesty, that hurts."

"Ah, s-sorry..."

"Fufu, you are the Queen, there is no need to shrink back so much."

"I cannot help it, it is a habit. Thanks to your strict training, I have mastered this tone, but deeply ingrained nature does not change so easily."

"So that was something you acquired through training."

I completely thought she had spoken with such a haughty tone since she was little—come to think of it, her older brother was supposed to inherit the throne at first, wasn't he.

"When Her Majesty was first crowned, she was around 10 years of age. Because she was a person somewhat lacking in dignity, I thought I should at least do something about her wording and behavior."

"10 years old... Nemusia, how old are you now?"

"I am 12."

She was younger than I thought...

Because her appearance is 16, I inevitably interacted with her with that image, but for a 12-year-old, this is quite admirable.

"Since Ikuna Yumemi is 16, I also felt a sense of incongruity with the physical body. However, the incongruity of dwelling in another person's body was far greater than the age difference."

"Dwelling in another person's body... is it. It seems there are many things we must discuss with each other. Shall we settle down and exchange information for now?"

"I was thinking the same thing."

"Umu, let us sit and talk."

Nemusia and I sit side-by-side on chairs.

Meanwhile, Librio, having opened his pages on the desk, emitted a mysterious light from there.

Then, the figure of a man in his late twenties with long hair was projected onto the opposite seat.

"Since I was subjected to the heartless word 'gross', let us talk in this form."

"That might be helpful."

"Are there no words of reflection or apology?"

"Because what's gross is gross."

"Haha, you are an unforgiving person. Um—"

"Kuragane Erika."

"Erika san, aren't you speaking rudely to Her Majesty as well?"

"Umu, I don't know how many times I have considered judging her for disrespect."

"It can't be helped. The Adrasia Kingdom doesn't exist in our world, so it's troubling even if you call yourself Queen. By the way, did they use Japanese in the Asrasia Kingdom too?"

Librio's face is completely non Japanese.

Nemusia is originally Yumemi chan, so there's no incongruity, but if that hair color is natural, she isn't Japanese either.

"I learned it from the humans here. To gather information, one must first understand the language, after all."

"I don't think you had that much time, though..."

"Librio is a genius said to possess the finest mind in the Adrasia Kingdom. Something of that level is a piece of cake for him."

"Her Majesty also seems to have mastered this 'Japanese', though."

"This was originally dwelling in my physical body. I did not learn it."

"Nemusia's body belongs to my best friend, after all."

"Best friend, is it. Could you tell me more in detail?"

First, I talked about the circumstances leading up to Nemusia dwelling in her current physical body.

Though, only as far as I understand.

Yumemi chan was used in the ritual for Giraiguu, and only her soul vanished somewhere.

After that, Nemusia's soul dwelled in the empty physical body—that is.

Therefore, while Nemusia is Nemusia, she is slightly influenced by Yumemi chan.

"Ikuna Yumemi, and Giraiguu... Regarding Giraiguu, the humans here frequently uttered that word."

"What are those guys doing? They were playing with a ball like kids."

"I would like to know what their goal is and where they came from. Well, thanks to their arrival, the rotting of the castle seems to have temporarily stopped, though."

"I think that's probably the result of merging with our school."

"It helps that it stopped rotting, but honestly, having the castle trampled on with muddy shoes is unpleasant. Moreover, they mistakenly believe this place is heaven or paradise."

"Don't tell me they're saying things like 'True World'?"

"Yes, exactly that. Do you know something?"

"This Giraiguu thing is a god that is said to destroy our world and lead believers to the 'True World' behind it. The appearance of the Adrasia Kingdom is quite far removed from our world, so maybe they saw this and mistakenly thought it was the 'True World'."

"And because of that, full-grown adults are frolicking and playing around like children, is it?"

I don't know yet what happened to the students who were caught up in this.

But at the very least, the teachers who were Kaisei kyou believers are ecstatic and going crazy upon coming here.

This is the True World.

As a result of doing the right thing, they were freed from all responsibilities and reached this paradise.

So all that's left is to enjoy happiness—misunderstanding it like that.

Ooki was also quite crazy, but my heart grows heavy thinking that there are several guys just like her frolicking around.

After letting out a big sigh, I instinctively spilled my true feelings.

"So gross..."

"Yes, it is gross."

Librio san also played along.

In his case, he's actually being shown that sight, so he must feel incredibly disgusted.

"Sacrificing the students they should have originally saved, and immersing themselves in the pleasure of fanaticism is also creepy. How foolish."

"Well, I'll kill them eventually."

"It would be helpful if you could promptly exterminate the pests. I have no power to fight, after all."

"Can even you, who was called the strongest magician, not fight with that physical body?"

"The amount of records that can be written in a grimoire is limited. Just transferring the minimum necessary functions took everything I had. Even so, since I maintained this castle preventing it from rotting, I'd like to be praised."

"Umu, such a feat could only be done by Librio. Does protecting it from rotting mean the collection of books is also safe?"

"Yes—I was unable to save lives, but I manage to save the records that the kingdom existed."

I see, Nemusia's soul dwelling in Yumemi chan means the physical body Nemusia originally had became empty.

In other words, the Queen Majesty he should have protected died first.

"It seems Kaigyo's corrosion preferentially eroded 'life'. So I abandoned my physical body, survived by sealing my soul in this book, and protected the castle with a barrier."

"You have worked hard, Librio."

"Being able to be directly appreciated by Her Majesty like this, it was worth pushing myself."

"In Nemusia's country, is extracting and sealing souls and such a common practice?"

When I asked that, Nemusia shook her head and denied it.

"There were magicians researching it, but they should not have progressed that far."

"Then what Librio san did—"

"I received guidance from His Highness Nyx."

"You mentioned earlier that you met my older brother as well. Moreover... after I left."

"Does Her Majesty not remember what happened at that time?"

"Nemusia seems to have gotten amnesia when she dwelled in Yumemi chan's physical body. She's remembering little by little, though."

"I see... Originally, preserving human memories is the brain's role. Even though a backup is taken in the soul, since she forcibly dwelled in the physical body of another person, it stands to reason that it requires time to regenerate them."

True, there's no way Nemusia's memories are in Yumemi chan's brain.

After dwelling in the physical body, the data stored in the soul was copied to Yumemi chan's brain.

"Then I shall tell you the events that occurred on that day."

"I might remember while listening. Will you tell me?"

Librio san rested his elbows on the desk, narrowed his eyes, and began to speak of "that day."

"I will say this first, but because 'time' is also dead due to the rot, please forgive me that I do not know the exact elapsed time. In my sense, it was an event about 3 weeks ago—"

◇◇◇

About a year had passed since the Heroes, and Kaigyo's Gangrene, were discovered in the Adrasia Kingdom.

By that time, the Gangrene had turned into impossibly powerful monsters, the Heroes' growth couldn't keep up, and humanity was slowly being cornered.

In the area around the royal castle, which had a relatively large military force, they tried to expand humanity's territory by defeating the master of the area and releasing the barrier, but by that time the surrounding areas had already fallen, and it instead resulted in allowing a massive influx of Gangrene.

Naturally, distant places with few soldiers deployed had perished long ago.

Humanity had no moves left to play.

Before they knew it, even the royal castle was surrounded by Gangrene, and the surviving Heroes and Apostles were barely holding off the attacks.

『Why... why is my older brother doing such a thing...』

Worrying in the throne room, Nemusia often said that.

Yes, the Kaigyo that attacked the Adrasia Kingdom—its core was her older brother, Nyx Adrak.

Previously, when he slaughtered the guards and appeared before Nemusia, he left behind words that could be called a "declaration of war against the world."

『I will destroy this hopeless world. I will kill everything and make it as if it never existed. No one can stop me. Because no one understands my suffering! But Kaigyo is different. Kaigyo acknowledged my hatred. It taught me the means to give form to this hatred!』

True to his words, he wielded Kaigyo's power and destroyed the world.

Nemusia was constantly thinking of a way to stop him.

For the country, for the world, and for Nyx.

In reality, there was also the reason that to overturn this desperate difference in military power, there was no choice but to persuade her brother directly.

However, after showing his face once, he never appeared again, and no one witnessed his figure.

Just waiting for destruction—while such time continued, screams echoed through the castle.

Blood spurts.

Lives scatter.

It was the same sensation as when Nyx appeared previously.

Even though the lives of precious soldiers were being taken, it's said that at that time, Nemusia wore an expression as if she had been saved.

And a blood-soaked Nyx appeared in the throne room—

『Older brother...!』

『Nemusia.』

He smiled gently at his sister, just as he used to.

To such a brother, Nemusia pleads.

『Already, it's enough already... surely, everyone is happy. The people who desired revenge too, sufficiently, already!』

She called out to Nyx not as a Queen, but as a sister.

However, his lethargic smile, as if he had thrown everything away, didn't change.

『It's too late. Everything, everything has already ended.』

『Older brother—?』

And Nyx tightly hugged Nemusia.

At the same time, his arm pierced her abdomen.

『At least you alone, please survive. I'm sorry... forgive your selfish older brother...』

『Older... b, r...』

There, Nemusia died.

At that time, Librio was in the throne room.

Frightened by the overwhelmingly massive presence Nyx possessed, he couldn't move a single step.

『Librio.』

『Kh... Your Highness...』

『I did not have the vessel of a King. I could not meet your expectations. I can only entrust myself to such an ugly thing and destroy everything. I'm sorry.』

Nyx pulled his arm out of Nemusia's corpse.

Then, a translucent mass was drawn out smoothly.

He held it up to the heavens, and sent it off beyond a hole that opened in space.

『What did you just do.』

『This world will end, just as Kaigyo and I desire. That is why I wished for Nemusia to survive, even just a little, in a place other than here.』

『I am asking what you did!』

『I sent her soul to another world. Although, it is a world eroded by the same Kaigyo. It is destined to perish soon as well, though.』

◇◇◇

Hearing that far, Nemusia let out a voice like "Ah..." as if she realized something.

"Did you remember?"

"Umu... yes, I was killed by my older brother, and after that... I was guided to a very cold and dark place."

"So you also remember when you were acting only as a soul."

"It was a terrifying place where, if I relaxed my mind even a little, I felt like I would be swallowed by the coldness and disappear. At that time, I just wanted to go to a warm place—and reached out my hand to another world very close by."

"And that was our world."

Should I think of 'only a soul' as a state like a ghost?

Without Yumemi chan's body, she would have had no choice but to wander without anyone being able to touch her; what was he planning to do?

Perhaps Nyx san thought that even such a state was better than dying in the Adrasia Kingdom.

"Kaigyo is written as 'Fish that devours worlds', to express it in your country's language." (TL Note: the literal translation of Kaigyo is World Fish)

"Kaigyo... huh."

"An image of a ferocious fish lined with fangs. Thinking like that, when being preyed upon by the Kaigyo, it can be considered that the Adrasia Kingdom and your world were in very close positions."

"Because it was being bitten by the adjacent fang, Nemusia came to our world via that fang, is that it?"

"That is likely correct."

From fang to fang—if you think she moved like that, the reason Nemusia dwelled in Yumemi chan's physical body also makes perfect sense.

Because Yumemi chan should also be the core of the Kaigyo right now.

What lies beyond traveling through the fang is naturally the physical body of the core.

"Fortunately, His Highness Nyx at that time seemed to maintain a relative degree of rationality, so I asked him in passing. What is the Kaigyo? What is a soul? Is it possible to manipulate it with magic, and so on."

"Uh... you've got too much nerve. This was right after Nemusia died in front of you, right?"

"Because I knew the end was coming."

I guess he wants to say he gave up and became defiant.

But it's not easy to ask the very person destroying the world.

"From there, it goes without saying. After His Highness left, the Heroes, whose hearts were completely broken by the death of Her Majesty the Queen, were defeated one after another, and let their hearts, and physical bodies, rot. Around that time, perhaps Kaigyo's Gangrene had also reached the limit of their evolution, their physical bodies began to collapse, and they began to rot away along with the world."

"If they evolve too much, they break."

"You could say it was a state where their entire bodies had become cancerous. Even though they were monsters, they were originally citizens of the Kingdom, so they were ultimately destined to die out and be preyed upon by the World Fish, I suppose."

And after everything died out, Librio san was the only one left alone as a book.

"A world with neither life nor death, filled only with silence—I didn't dislike it because it was easy to concentrate, but that state didn't last forever. A short while later, unidentified humans appeared in droves."

"It merged with our world."

"Because I moved from the Kingdom to Hikarinomiya Academy, a connection must have been born. This physical body is connected to Ikuna Yumemi. In other words, my soul is connected, albeit indirectly, to the core of the Kaigyo."

Another conceivable possibility is that it wanted to avoid involving Hikarinomiya City more than necessary—maybe.

The academy, being the center, is one thing, but Fantasy Land was dragged in because of my and Yumemi chan's memories.

Hikarinomiya City is a shitty place, but even so, many beautiful memories we made together still remain.

I don't want to involve such places any further.

That's why, in a sense, the "unrelated" Adrasia Kingdom was made a sacrifice.

"Her Majesty also seems to have remembered. I am glad that I was able to fulfill my role of passing down records, true to being a book."

"Can I ask you a few things I'm curious about?"

"I do not mind."

"I understand that Nemusia's older brother became the core of the Kaigyo. But what is the core of the Kaigyo in the first place? If it just eats worlds, it doesn't need to do something like that, does it?"

"To explain that, it is necessary to talk about the ecology of the Kaigyo."

Ecology—well, since it's called a fish, it must be a living creature.

Moreover, an unfathomably large one, capable of devouring a world entirely.

"In the first place, do you know what a world is, Erika san?"

"A world, you mean a planet?"

"No, the 'world'. If I were to explain it in a way tailored to you, for example, a planet floats in space. That planet is part of a galaxy, and that galaxy is part of a supercluster, and the supercluster is also just a part of the universe—or perhaps, the universe is also just a part of something else."

"Sorry, I'm not very knowledgeable about that kind of talk."

"You may ignore it. Librio has a bad habit of showing off his knowledge and making stories complicated."

"And Your Majesty often dozed off in my classes since the old days, didn't you."

"Your stories are too difficult!"

"Now, now, both of you. I get that you've known each other a long time, so let me hear the rest."

"Yes, let us get back on track. Anyway, let us temporarily call a lump of such things a 'world'. However, no matter how much Erika san continues to search that world, you will never find our Adrasia Kingdom."

"Because it's an alternate world."

"Exactly. Our world is, so to speak, like a bubble floating in the sea. Countless numbers of worlds exist in a vast space."

Librio san, speaking like that, seemed awfully happy.

He said he could concentrate when alone, but Nemusia said he likes to show off his knowledge, so he might be a person who likes teaching things to others.

"Furthermore, on a different axis, 'worlds of different possibilities' are lined up in a row."

"Parallel worlds?"

"Erika san, you are quick to understand, good. Yes, parallel worlds. And on yet another axis, worlds arranged in chronological order are lined up in a row."

"So if you could move along that axis, you could go to the past or the future?"

"I would not say it is impossible. What is important here is that worlds increase by the amount of possibilities, and worlds increase by the amount of time. And a massive amount of alternate worlds are also floating in the sea."

"Then, wouldn't the world continue to expand infinitely?"

"It does expand. But the sea is vast enough that it is not a problem. Besides, there are existences that clean up the increased worlds."

"...Does that mean the Kaigyo?"

Hearing my words, Librio san smiled.

Wait, then that means—

"It's not that someone is doing something bad, but the Kaigyo is just... having a meal?"

"From the Kaigyo's perspective, our world is like plankton floating in the sea."

"A-Are you saying the people of Adrasia were killed that easily!?"

"Living creatures kill numerous other living creatures just by living. This applies not only to humans but to all life. The world is just something like that."

He says slightly dismissively.

He too is a human who wanted to protect the Adrasia Kingdom even if it meant sacrificing his own life.

He must have also been indignant at that unreasonableness at some point.

"I understand what Erika san and Her Majesty want to say. Like, if we defeat someone. Or, someone is at fault. You are looking for such an 'end'. However, that is not the case. The Kaigyo is, so to speak—"

But Librio san has long passed that phase and given up.

Because he has come to understand that there is nothing that can be done.

"An unstoppable natural disaster."

I've heard the phrase that nature is the scariest thing.

The Kaigyo is a type of that disaster.

Although it is a lifeform, the dimension it lives in is too different, so it hasn't even reached the realm of whether one can resist it or not.

"While it does have a habit of 'liking the smell of human hatred', there is no malice there. Of course, His Highness Nyx is not to blame either. Considering his circumstances, it is only natural to hate the world. It just so happened that it was accidentally found by the Kaigyo."

"Why does it go out of its way to create something like a core and sacrifice a human?"

"The dimension they live in is different. The Kaigyo is a fish swimming in the sea where worlds float. To prey on our lives, it must first capture a lifeform of our world and 'downscale', otherwise we are too minuscule for it to interfere with."

The core is, so to speak, a terminal to spread the rot.

And the rotting process is likely something akin to digestive fluid.

"It might seem unreasonable. However—worlds exist infinitely. The probability of a world being eaten by the Kaigyo is infinitely close to zero. Even if a strong 'smell of hatred' were being emitted, if a Kaigyo is not swimming nearby, it will not be attracted."

"Then... in the end, the cause of the Adrasia Kingdom perishing is..."

Librio san laughed lethargically—and said with an expression that was probably "unlike him."

"We were unlucky."

Coupled with his expression, those words must have resonated heavily in Nemusia's stomach.

Even I felt my stomach hurt a little, so she, being the party involved, must surely find it even more painful.

Under the desk, I grasp Nemusia's hand, who had her eyes wide open in a daze.

Then, perhaps her frozen heart melted a little, her expression crumpled—

Tears welling up in her eyes, Nemusia muttered, "For such a ridiculous reason..." and bit her lip.