The shining doorway flashed as Aeon, Twilight, and Starlight stepped through, disappearing behind them and leaving only three more doorways in the Nexus. The cobalt unicorn mare chuckled in response to Starlight's surly demeanor.
"You said you'd be right there with us!" Starlight growled, rounding on Aeon almost as soon as they entered the Nexus, "instead we were left there alone! We could've died or something!"
"You wouldn't have died, Starlight Glimmer," Aeon replied with a roll of her eyes, "Chrysalis knew you were coming and knew what you looked like already. She wouldn't have attacked you, her changelings wouldn't have attacked you, and she would've kept any dangerous creatures in the caves from attacking you."
"Well... how were we supposed to know that?" the indignant pink filly retorted, "we were terrified!"
Aeon sighed and rubbed her temples.
"Look," Aeon began, "sorry for bailing on you two, but something came up that I had to personally deal with right then."
"What could've possibly happened in the few seconds that passed while we went through the door?" Starlight asked with a skeptical raise of her brow, "you were ready to go when we left."
"No I wasn't actually," Aeon replied with a shake of her head, "in fact the issue I had to deal with started about a minute or so before you went through. The only reason I didn't leave to go deal with it right then was because I needed to make sure the doorway was stable before you went in."
"Oh," Starlight replied, lowering her ears and looking away. She perked back up and snapped her gaze back to Aeon a moment later, "wait, then why did you lie to us and tell us you were coming?"
"To get you two moving," Aeon replied simply, "honestly, I was about ready to throw both of you through the doorway with how much you were both hesitating, but now that the crisis is over, there's no need."
"What was the crisis anyway?" Twilight asked worriedly, "is everypony okay?"
"Aw, you're worried about ponies you've never even met?" Aeon cooed, leaning over to muss up Twilight's mane, "that's so adorable!"
"Hey!" Twilight cried stepping out from under Aeon's hoof and shaking her head roughly before glaring at her mentor, "I'm serious! Was there some kind of monster attack or something?"
"Something like that," Aeon replied cryptically, "you'll probably see once we get back, but right now that's not for you to worry about," she motioned for the girls to follow as she made her way over to another door, "right now, it's time to meet your next tutor."
"Are they gonna be as... creepy, as Chrysalis was?" Twilight asked nervously, "are all of our teachers gonna be like this?"
Aeon's chuckle did nothing to reassure the lavender filly.
"Ah, they're alright once you get to know them," the mare replied with an airy wave of her hoof, "that said, your next teacher can be a bit... strange."
"What's that supposed to mean?" Starlight grumbled.
"Well..." Aeon paused in thought, "he... comes from a different time. Back then, ponies were more... ah... theatrical in their speech... I guess," after a moment she shrugged, "you'll see what I mean when you get there. Any questions?"
There was a second of silence before Twilight spoke up, shifting from hoof to hoof uncomfortably.
"So... you and Chrysalis," she began hesitantly, "are you both like... y'know..."
"What? Me and Chryssie?" Aeon replied, raising an eyebrow before giving the filly an amused smirk, "we're not in love if that's what you're wondering. It's more like... oh, how do I explain this to a filly?" she tapped her chin thoughtfully, giving a simple shrug a moment later, "we have fun together, nothing more, nothing less."
"Fun?" Twilight asked, tilting her head in confusion, "what kind of fun? What do you—"
"Moving on," Aeon interjected as she stepped aside and gestured to the doorway before them, "this time around you won't have to worry about me lying to you girls," Aeon assured, much to the fillies' relief, "...because now I'm flat out telling you you're on your own."
The relief was quickly washed away by shock and incredulity.
"Are you serious?" Starlight practically screeched.
"Yup," Aeon replied cheerfully before lighting up her horn, "Say hi to tall, dark, and spooky for me~"
Before either filly could say or do anything else, they were both wrapped in a yellow aura and promptly tossed through the doorway.
Both fillies landed in a heap and struggled for a moment as they tried to recover.
"I can't believe this!" Starlight cried, untangling herself from Twilight and rising to her hooves, "she just... threw us in! What kind of teacher is she?"
"Um... Starlight?"
"And just what the hay did she mean tall... dark... and..."
She trailed off as she finally took notice of her surroundings. Twilight stood next to her, the both of them staring wide eyed and open mouthed at the sight before them.
A castle, taller than any the two had ever seen, towered over them. For Starlight, she had nothing to compare it to other than the castle she had seen back in the Core. For Twilight, it wasn't as spread out as Canterlot Castle with it's many spires and separate buildings, but it made up for it with the sheer intimidating height of the few spires the castle did have.
They stood before the massive ornate double doors in silence—that is, until Starlight turned to get a look at the scenery around her. Something had looked odd about the castle, and really everything in general, but she hadn't been able to put her hoof on just what.
It was when she was able to actually see everything other than the large doors taking up her vision, that she realized what it was. She nudged Twilight, getting the filly's attention and causing her to follow her gaze.
They both stood at the top of a steep, long stairway leading further down into the city surrounding the castle below. The city itself was massive and—though the colors were dull—the whole city seemed to glow with an inner light.
The various buildings all appeared to be carved out of some kind of crystalline material and they all came in different shapes and sizes. The castle also seemed to be a crystal-like structure, but that wasn't what caught and held Twilight and Starlight's attention. What had caught their attention, and what Starlight had realized was wrong, were a few other things.
The sky was completely devoid of any Sun, moon, or stars. It was a pitch black canvas of nothingness that enveloped their entire view. The second thing that was made abundantly clear was the complete and utter lack of any sound whatsoever.
They hadn't noticed it when they first arrived, but whenever they spoke, their voices carried a sort of muted echo, that seemed to quickly wither and die in the face of such overwhelming silence.
By far the most noticeable thing about their surroundings however, were the countless shadowy silhouettes moving about the streets below. They were all pony shaped and trotted about soundlessly and aimlessly—occasionally stopping and looking around as if they didn't know what to do or where to go.
Twilight turned away from the eerie sight and looked to Starlight with an unnerved expression.
"Where are we?"
"How am I supposed to know, Twilight?" Starlight replied, not taking her eyes off the shadows moving below, "this place is even creepier than that cave," she finally returned Twilight's gaze with an uncomfortable look of her own, "I don't want to be here."
"Neither do I," Twilight agreed, taking a step back from the staircase and towards the double doors, "but what are we supposed to do? Aeon just left us here and we don't have a way back."
"Well..." Starlight hesitated and her ears flopped against her head as she looked from the city below to the double doors behind her, "I... guess we have to find this tall, dark, spooky pony."
"And he's probably in the castle," Twilight replied, fully turning back towards the doors, "I really don't want to go in there."
"Me either," Starlight responded before taking a few steps forward and placing a hoof on the door, "but we don't really have any other choice," she swallowed nervously and began to push the door, "let's just... get this... over with!"
Starlight grunted as she pressed her hoof to the door, then both hooves, then she threw her body into it. She pushed with everything she had, but no matter what she did, the doors didn't budge.
After a minute she stepped back and glared at the door her chest heaving slightly.
"What... the hay?" she panted, "it won't... open!"
Twilight's brow furrowed and she stepped forward to give it a try, meeting the same result as Starlight.
"I don't get it," Twilight muttered, scrunching her face up in confusion, "wasn't he supposed to be expecting us?"
"Indeed I was, little foals."
The sudden deep rumble of a voice made the two jump with a yelp and they quickly searched for the source. They saw nothing and looked at each other with no small amount of fear in their eyes. Their ears perked up as the voice chuckled and spoke again.
"You seem to be having some trouble, young ones... here, allow me."
The two screamed as a swirling black something rapidly spread below them. Both their screams were cut off as they were instantly sucked into the black mass—the screams resuming once more as they re-emerged in a completely different location mere seconds later.
The fillies continued to scream and babble in a panic for a moment longer before they realized they weren't being attacked or otherwise affected by anything else. Having calmed down somewhat they looked around with wide eyes.
Though she had never been in one before, Twilight immediately recognized the long stretch of carpet, tall stained-glass windows and pillars, and the overall massive size that made up a throne room.
Not having grown up in a castle town, Starlight had no such knowledge.
"W-Where are we?" she asked in a shaky voice—her fearful eyes darting this way and that, "Twilight... what happened? Where did—"
"And thus... we finally meet, Twilight Sparkle... Starlight Glimmer."
The two snapped their gazes towards the back of the large room. A few yards away they could see a large throne. Everything around the throne looked to be enveloped in large black crystals.
Reclined atop the throne itself was a tall grey unicorn stallion in menacing silver armor and a red cape—though the fillies had never seen a stallion quite like the one that sat before them. His horn, rather than the color of his coat, was a blood red color that brightened to a dark orange as it reached the tip.
His mane and tail were jet black and billowed about him in much the same way as Celestia's did. Even from a few yards away, the stallion's piercing gaze sent chills down the fillies' spines.
Twilight knew a few things about Dark Magic, and the slitted red pupils, glowing green sclera, and purple mist wafting from his eyes spoke of complete corruption—at least from what she had read. The sheer wrongness of the stallion's aura would've been enough to give his corruption away even if Twilight hadn't known a thing about Dark Magic.
Once the stallion saw that he had their attention he slowly rose from his throne and trotted towards them at a leisurely pace, an intrigued smile playing across his muzzle.
"Aeon has told me much about you two," he began as he made his way towards the slowly retreating fillies, "she tells me you both are quite... prodigious in your magical capabilities..."
His piercing gaze flicked towards Twilight, causing the lavender filly to freeze in place, breath hitching and eyes widening in fear.
"...especially you, Twilight Sparkle," he continued, not taking his eyes off the filly, "I was told of a very interesting vision the two of you shared, and I must say... if even half of what I've heard is true, you shall make quite the Dark Mage when you've fully developed your affinity."
He leaned down towards Twilight, his smile turning wicked.
"You might even be a match for my own power someday," he straightened up and stepped back with another small chuckle, "and that my dear filly, is a future I very much wish to see come to fruition."
"W-Who are you?"
The stallion looked towards the light pink filly that had spoken. Starlight winced and shrank back as his full attention fell upon her. Nevertheless, she swallowed and spoke again.
"A-Aeon... Aeon never told us your name," she continued haltingly, "and... a-and you're supposed to... t-to be our teacher... so..."
"Ah, yes, you must forgive me," he turned on his heel and trotted back towards the throne, "it has been... quite some time since I've had anyone other than that mare to talk to."
He sat once again on his throne and beckoned the fillies forward. The two gave each other worried glances before reluctantly trotting closer to the stallion's throne.
"Come, there is much I wish to discuss regarding our arrangement, and though I am eager to begin, we do not have the luxury of time," he paused and gave an irritated snort, "I suppose it would be more accurate to say that the two of you do not have the luxury of time."
Twilight wanted to ask what the stallion meant, but chose to hold her tongue this time. Something about both the stallion and this place bugged her, and she felt as though it was something beyond the cloying stench of Dark Magic and the unsettling atmosphere of the city.
"Aeon merely stated that this was to be a simple introduction and nothing more," the stallion continued, "so, Twilight Sparkle... Starlight Glimmer... allow me to introduce myself..."
The stallion sat up straighter on his throne, his tone suddenly booming and imperious.
"I once reigned supreme as the ruler of the Crystal Empire. Many knew me far and wide as the King of Monsters, however, while you two are under my tutelage, you shall simply refer to me.... as Sombra."