Inside, it looked like an ordinary school, but beyond the half-destroyed wall stretched an endless horizon, a bizarre scene for a classroom.

In this space, both familiar and utterly surreal, a girl's energetic voice rang out.

"Sensei! Today, I, the super-competent Arona, want to tell you about a very important hypothesis I've come up with!"

"Oh, a hypothesis from the super-competent Arona? I'm excited to hear it!"

Perhaps accustomed to the blue-uniformed girl's random remarks, the man who had been abruptly summoned here readily agreed with a smile. Hearing this, Arona, the main OS of the <Shittim Chest>, grew even more enthusiastic and confidently continued.

"It's about the three mysterious figures who have been the talk of Kivotos in recent months!"

"Three mysterious figures...?"

As Sensei tilted his head and asked for clarification, Arona boldly stretched out her hand and began to unfold her fingers one by one.

"Yes! First, the coordinator of the underworld, commonly known as <Pitch Black>!"

"Ah, the one everyone in the underworld trembles at just hearing their name? I heard Aru met them once, and even though she tried to hide it, her envy was written all over her face."

"The archenemy of the Decagrammaton's prophets, whom they call the 'Usurper,' <Pure White>!"

"Hmm... According to Himari, who investigated them, said there was no evidence of their existence, suggesting they might be a manifestation of the prophets' fear itself. It's also unclear why they're called the 'Usurper'."

"And finally, the network troublemaker who pops up everywhere online, <Ash Gray>!"

"A wanted student as a terrorist... but aren't they more of a playful hacker?

The actual terrorism was committed by other students provoked by them. Still, seeing Haruna so get so angry was a rare experience."

As the girl unfolded her fingers, pointing to each figure, the man briefly recalled the information he knew about them.

"Come to think of it, all three have strangely no connection to our Schale. Even when there was a chance to meet them directly, they vanished as if avoiding us."

After remembering this recent doubt, Sensei smiled at Arona again and asked,

"So, our super-competent Arona, what's your hypothesis about these three?"

"Hehe, Sensei. It's that... all three of them might be the same person!" "..."

Following the girl's energetic exclamation, a moment of silence filled the classroom.

At the same time, another figure in the distance flickered slightly, but neither Arona nor Sensei noticed this subtle movement.

"I see, Arona."

"Your energy dropped?! And what about 'super-competent'...?"

To Arona, who was flustered by the unexpected reaction, her Sensei explained with his usual kind smile.

"But Arona, even if we ignore that their abilities and areas of activity are completely different, the personalities of the three we know, even if only partially, are vastly different, aren't they?"

"W-well, that's true, but... Ah!"

Arona, who had been pouting after being silenced by Sensei's logical rebuttal, turned her head sharply, looking for someone in the classroom to support her.

"Plana-chan!"

Right after politely greeting Sensei, Arona turned to the second resident of this space, who had been sitting quietly, engrossed in reading while she was talking.

"..."

Long, snow-white hair flowing down to her knees,

A black winter uniform contrasting with Arona's blue summer uniform,

And deep, intelligent gray eyes that gave off a mysterious vibe.

Tap.

"What is it, Arona-senpai?"

This white-haired girl, who shared the role of OS of the <Shittim Chest> with Arona, closed the book she was reading and responded to the call with a tone as stiff as her cold expression.

"Aw, you were listening, weren't you, Plana-chan! Besides, don't you think calling me 'senpai' is too formal? How about 'big sister'-"

"Senpai is senpai, senpai."

"I-immediate response? And did you have to emphasize it three times?!" Arona exclaimed in protest, stamping her feet, as her proposal, which she had made countless times to her junior, was once again flatly rejected.

"Haha, you two always get along well."

"Hehe, of course! I take such good care of Plana-chan!"

However, when Sensei smiled and praised them, Arona replied with a bright smile, as if she had never been pouting.

"...Affirmative."

And this time, the girl in the black uniform also agreed with Arona, albeit in a small voice. Sensei watched their interaction with a warm smile for a moment and then turned his gaze to the textbook Plana was reading, which he had uploaded to the Shittim Chest upon request.

"Plana, you're always studying hard."

"Yes, Sensei. It's a student's duty."

This time, the white-haired girl calmly bowed her head in thanks for the man's admiring praise.

"Ugh... I should be setting an example as the senior, but how does Planachan read those difficult books so effortlessly?"

"...Senpai, as I've told you many times, waking up early in the morning is the top priority. Didn't you oversleep again today?"

"Ah, ehehe..."

Arona briefly whined with a hint of envy towards her always-exemplary junior, but she could only scratch her head with an awkward laugh at the subsequent remark. They were completely opposite in personality and appearance, yet at the same time, they seemed like close sisters.

"So, Plana, what do you think?"

Sensei, who had belatedly recalled the previous topic after enjoying the cute scene, asked Plana for her opinion without any particular expectations.

"About Arona's hypothesis that <Pitch Black>, <Pure White>, and <Ash Gray> are all the same person."

"..."

Plana, unusually, paused for a moment, then lowered her gaze slightly and spoke slowly.

"...Answer,the possibility is extremely low."