Spike walked into the castle's main library to find several tomes swirling about, surrounded by various hues of aura. Sunset and Midnight had decided to dedicate the last day of their vacation to learning whatever they felt necessary, with Twilight and Starlight's help.
"I got those muffins you requested, Twilight." Spike said as he ducked underneath an unusually zealous book, glancing over at the violet mare who claimed it.
"Sorry, still not used to the horn just yet," Midnight said as she began sifting through the pages of her prize, a rather elaborate spellbook that Sunset quickly recognized.
"You're probably not going to be able to attempt anything in there, those are some very high-level spells," she said as she gripped the book in her own red aura.
"Maybe not on this side of the mirror," Midnight retorted, "but I'm rather curious as to whether or not they'd be possible on the other side with the increased ambient magic."
"I wouldn't recommend trying," Twilight interjected, Sunset noting that they were both thinking the same thing. "If magic is continuously leaking through, then it's probably best not to try anything that might draw it out more. We still have no clue what's going on with the portal, and until we do I've decided to take every precaution necessary to slow down the process."
Midnight's only response was the defeated look she now wore.
"Aw, don't be too disappointed. I'm sure we'll figure things out before long," Sunset reassured her. "In the meantime, I'm sure Starlight here could teach you some more fundamentals. There's still quite a bit for you to learn."
Sunset was glad Midnight had taken that offer; it meant she had some free time to investigate her own suspicions.
First things first, she thought as she discreetly pulled out the device they used to track ambient magic around the Canterlot High statue. It had constantly hummed during their stay due to the ambient magic, but now it spiked far higher than it had been, making Sunset certain that magic was leaking through this side as well.
She heavily debated whether she should relay this information to Twilight, or to keep to herself and do her own research. She was certain Twilight could help, but telling her meant she would likely bring her friends into the fray to ascertain Sunset's suspicions, and things could go downhill quickly from there. Besides, she still had no clue what her observations meant.
She decided to continue her own research first, and if she found any leads or connections, she would inform Twilight of them. For now, she levitated down what appeared to be a copy of Starswirl's notes on the matter. It was highly likely that Twilight had read and reread this several times and would tell Sunset of any important info, but Twilight was also prone to missing key details when she was excited, and just owning a Starswirl notebook was enough to make her giddy, so for her own assurance, Sunset decided to examine it for herself.
What she found was... interesting, to say the least. Several pages had completely unrelated notes on them, making his connections hard to decipher; it seemed as though he never worked on one thing at a time, content to just jot down notes on whatever project he fancied at the moment. At the top of one page was a diagram for a portal housing, much like what held the mirror in place, but below it was suddenly the crystal matrices required for elemental empowerment, as well as a note for a reference. It made Sunset's mission much more tedious than she would've liked.
However, she did find some notes relating to the matter, and what it was nearly sent her into panic.
"I don't know what fundamentals Sunset is referring to, I've already learned the basics of how to use my horn, and I can levitate stuff! What else is there?"
Starlight shook her head, only now understanding just how little Midnight knew despite her burgeoning prowess. "I think what she was referring to was the various schools of magic. Learning a spell isn't as simple as memorizing a few symbols or incantations, unicorns can be more adept at some more than others. For example, Shining Armor is more adept in abjuration; more specifically, shield spells."
She continued on to describe them in more detail. She stated that abjuration was the school of protection, usually including shield spells, mana deflection and the more advanced version of a teleport spell that allowed you to target somepony other than yourself. Conjuration was the school of summoning, though its use was nebulous at best, having been deemed as cruelty to those subjected to it. Divination was the school of the mind, and basically summed up Sunset's abilities in one word; it made Midnight wonder if that was Sunset's proficiency or if her empathic abilities came separate from her own magic.
Enchantment was relatively straightforward, though Starlight mentioning that these spells could be applied to ponies as well was a little unnerving to Midnight. Evocation really got Midnight excited, subtly dubbed the school of the elements, its magic used to, as Starlight put it, "create something from nothing". Midnight gathered that it was raw energy manipulation, more often than not transforming into an elemental attack; what kind it was generally depended on the wielder.
Transmutation was, again, straightforward, summed up as transformation magic, and what Twilight most commonly practiced during her time in Ponyville. Midnight found that interesting, wondering what use Twilight would have for such spells before Starlight mentioned the 'mustache' spell, sending both ponies into a fit of giggles.
"And that just about covers all of the ones practiced in the modern age," Starlight finished before a slightly solemn look took hold. "There are also necromancy spells out there, but its been outlawed for centuries, for obvious reasons." That simple declaration sent a shiver down my spine, before a louder voice caught my attention.
"YOU NEVER TOLD ME THIS HAPPENED BEFORE!!!"
Sunset was absolutely livid.
There in the notebook, written plain as day, was a recording Starswirl took of another mirror, noticing its continued use causing deterioration on both sides, as well as a hypothesis that further use would cause the two realms to converge, with no understanding of what would occur after.
And Twilight had access to this information for Celestia knows how long, and never said a word. Now that Sunset thought about it, she never mentioned having the notebook either.
"Why?! Why would you hide this, when this is the best lead we possibly have?!"
Twilight shifted uncomfortably in her position, memories of the other portal seeping back into her conscience, It had been a year or two since those events, but still...
"ANSWER ME!"
Twilight regressed from the shouting, still at a loss for words before stammering out, "I-it was all so vague about it, I wasn't sure t-that any of the hypothesis was relevant. He noticed the same thing we are, and drew a rational conclusion."
"But you never mentioned the consequence! Twilight, if the worlds converge, that would be absolutely disastrous! And here I was only worried that more magic was seeping through, but no, my home is slowly turning into Equestria!"
Twilight found herself without words again as Sunset turned away and stormed out of the room, the gaze of the other two slowly turning to Twilight. The princess herself was unsure of what to make of the situation until Midnight spoke up.
"How long have you had that notebook?"
Twilight elected to remain silent, her own mind battling over whether or not it had been a good idea to keep Sunset in the dark. On the one hoof, the only relevant bit of information held within was the hypothesis of what could occur, and Twilight had deemed it too much for Sunset not to freak out over. She had enough stress on her plate just fighting to figure out what was going on; topping it off with a world-ending scenario just didn't seem like the best choice.
And yet, it would've driven her to take things more seriously. Not that she wasn't already, but when it came down to it, Sunset could use every little bit of motivation she could get. Twilight still got the impression that Sunset still had self-worth issues, and possibly wouldn't see the investigation through to the end unless she absolutely had to.
But to tell her the worlds would collide? That magic would bombard the landscape, reshaping whatever remained of the human world? Everypony now facing a duplicate of themselves?
Or would they?
It dawned on Twilight that Starswirl never mentioned what happened to the populace, and it would be very well possible for duplicates to exist, or for the counterparts to be fused to one another.
But which side would continue to exist?
"Twilight, please."
She was snapped out of her train of thought by Midnight's insistence, sighing as she knew she have to explain it anyway, or they would find out for themselves.
"I've had it for at least a year now, but I didn't want to worry Sunset any more than she already had been. I believed telling her how high the stakes were would only make things worse at this stage."
Starlight and Midnight exchanged glances before turning back to the princess, Starlight stepping forward to her.
"Seems you still have a lot to learn, too."