She placed that mirror in the cellar for a reason.

To seal it away properly, and prevent any further damage, both to the mirror itself and her fellow Numberblocks.

She had even kept it away from the rest of M.I.15, making sure that it wouldn't land in the wrong hands.

But even after all of those precautions, Fifteen still wondered what it could really do. What possibilities it would reveal, and how things would change if she would've continued the investigation.

Twirling a pencil in her inexistent fingers, she glanced off into the ceiling of her office.

Her files were all sorted out as she would've wanted them to, rendering her with nothing to distract her from these thoughts.

A slight creak of a door opening snapped her back to reality.

"Fifteen?"

"Twenty-One! I didn't notice you there..."

The eponymous Number Explorer had came inside with a stack of files in her hands, still in her step arrangement as she had came in a hurry.

"It's alright...I was just about to clear out these paper files, since we've already transferred most of them to our database."

Ever since Seventeen set up a database for M.I.15, most (if not all) of the operational information was transferred there, rendering the paper file format to be purely used for interviews.

The original Step Squad had looked though all of the uploads herself to ensure that nothing important was left out, but she couldn't ease the feeling that something would still be skipped in the process.

A double check wouldn't hurt too much, right? That's what she thought.

"...I'd like to look though them once before you clear them out. Can't have something be accidentally erased, can we?"

Twenty-one smiled as she placed the files on the table. "I'll leave that to you, then. Better hurry back before—"

Seemingly on cue, a loud thud could be heard outside of the room.

"I-I'll get back to you soon!" She had already ran out of the room, shooting off towards the direction of the stairs.

Fifteen let out a small sigh, taking a few files from the stack as she started to flip through the records.

She had a feeling that this would keep her busy for a while.

=====================================================

By the time Fifteen finished half of the stack, night had already fallen upon Numberland.

Most of the agents have already gone off duty, signing off early to prepare for another expedition...she was among the few of those who'd stay late for their own projects.

She could probably finish checking the other half before sunrise, if she were to get going with the progress.

As she took out another file from the stack, the one below it had slid to the floor.

"Oh, whoops."

Picking it back up, Fifteen immediately noticed the excessive notes and doodles on the front cover of the file.

One of the written notes had caught her eye.

"...Only theoretically accessible though mirror? What does that mean by—"

A thought clicked in her mind, causing the Step Squad to immediately flip open the file in curiosity.

The file was about something dubbed "The Other Side", which was something that Twenty-One had started investigating on for a while. Printed pages from books and stories were attached to the case files, depicting the impression of a parallel world.

A parallel world that's similar to Numberland, yet vastly different than the world that they'd all be accustomed to.

Knowing Twenty-one, this would surely be something that she would be fascinated with.

It's not like her to just leave an investigation like this, though. She found it rather off.

Fifteen thought of just leaving it behind, since she still needed to finish checking the rest of the files.

Her intuition told her otherwise.

"Come on, Fifteen...just focus on the files. You'll still be able to get this done if you stop this now..."

It was starting to get even harder to get it out of her head now.

She probably shouldn't have looked.

Ah well. It's too late to regret it anyways.

===================================================

She'll just come back to the mirror, and test it once.

If it fails, she could just forget about it all.

Forget that she even had that thought in the first place.

Approaching the broken mirror, Fifteen took in a deep breath before pulling off the black fabric, revealing its fractured surface.

"Alright then...if I just do something like this..."

She had placed a hand over one of the larger pieces, making sure not to accidentally move it over to the cracks.

The darkened reflection had rippled slightly upon contact, as she would then feel a slight stinging feeling.

She would've trusted her intuition, and continued to press on.

Soon enough, she was able to see something from the rippling surface.

Something resembling a tower.

A tall, thin tower that seemed to glitch in and out, with dark clouds surrounding it.

Something that definitely isn't located on Numberland.

She was about to attempt looking into more places when she suddenly felt a strong grip on her hand, trying to pull her inside.

Fifteen had flinched so hard that she fell backwards, only catching her balance last-second.

...well, at least she got something out of that experience.

Looking back at the files, she wondered if further investigation would still be worth it—even if it wasn't going to be official.

In the words of Twenty-one...there's always more to explore.

But in this case, Fifteen wasn't too certain about it. Not anymore.

She just hoped that all of this would come at a lesser price.

Both for her...and the rest of Numberland.