Umbra stepped up to the threshold of the mirror. "If this turns me back, I will be so mad." But the idea of it wasn't enough to hold her back. "Twi would do it for me." Come to think of it... "She already has." And in she went, plunging into the strange warping tunnel between realities. Her body felt like it was being stretched and compressed at the same time, forced to comply with the rules of the world she was entering.
That place had no room for alicorns. She suddenly felt something hard and flat as she flopped out on her belly on cold concrete. "Ow." It hadn't hurt that much, more surprise really. "I'm alive!" She had made it, still breathing. That was a victory, right?
She pushed to her feet, wobbling. Her balance was off, but she had been a human before, so the biped life wasn't entirely foreign to her. "Twilight?" There was no Twilight around. She looked down to see two human breasts, but also arms that felt too long, and legs too. Her proportions were... not right. Her skin was a deep grey, like her fur had been. That was also not a natural color for a human. Were they human?
That world had also casually given her clothes. Nice of it. She was wearing a business suit with her cutie mark sewn in at the hip. "That's just adorable." She patted herself down with a smile. "I feel super professional." She was also an adult. She was an adult human(?) female. "And I've gone to school."
More accurately, she seemed to be in front of a school. "Huh." Well, random adults didn't belong at a school, so, cover story! "This may not work, but..." She strolled towards the front door purposefully. "I'm not going back yet." She grabbed the door's bar in her hands, which was a thing she hadn't had in a while. "So wriggly." She spent a moment just enjoying the feel of flexing fingers, but she had things to do! She pushed the door open to slip inside.
"Can I help you?" There was another person.
"Celestia?!" burst Umbra before she could think better of it.
"That's me," allowed the almost alarmingly tall lady with the same color hair and a skin tone that matched the pelt of the original. "I'm afraid I don't know your name, miss...?"
"Umbra." Umbra put out a hand towards the fellow adult. "I was told about you, all good things, I promise."
"That's good to hear." Their hands met in a friendly shake. "Are you the substitute?"
Well, that was a fine excuse. "Yep! I was going to go looking for you, but you found me. I was amazed at the luck."
Celestia's expression became more kind. "That explains that. No need to head to the office." She drew out a pen for pointing. "The class is third period, so you aren't late. Let's go review what the class was in the middle of learning."
"Great idea." She followed after Celestia. Yes, things were going well. She'd have things figured out. "Say, is there a student here with really bright yellow and orange hair?"
"That is not a lot of information to go off of," laughed Celestia. "Especially these days with hair dyes. My students love their colors, and I'm not discouraging them."
Stuffing her hands into her pockets, Umbra discovered she had a compact. A gift from that new world? Her tiara was also still on her head. "I can't throw rocks from this house," she joked. "I love a little extra color."
"Something that brings us together." She opened a door but didn't step through it, instead pointing at that tiara. "That...--" Umbra tensed with worry. "is gorgeous." Celestia clapped her hands together with a bright smile. "I don't know many that'd wear such a delightful bit of jewelry out just... for work. Aren't you a little overdressed for the situation?"
"Dress for the job you want." Umbra fired a finger gun at the principal. "One day, queen."
Celestia laughed at the idea. "You have a long road ahead of you then, but keep at it. For today, we will help shape young minds." She headed inside into the empty classroom. "They were just going over trigonometry."
Oh no. Math?! Of all the classes... "Soh Coh Toa!" blurted Umbra, the first thing that came to mind. "Let's learn. Well, let's help them learn."
"Good attitude." Celestia showed where the lesson plan had been. "You don't have to follow it exactly. You're not the teacher, but if you can help keep these things fresh for when the teacher returns, that would be ideal."
"I am on the case." Umbra clapped her hands together and settled at the teacher's desk. "I'll review this before they show up."
"Love the work ethic." And off she went. Celestia had other things to do, and that substitute seemed well in hand.
A pity the actual substitute showed up not long after.
He looked quite confused. "Huh? Oh, another class?" It wasn't that period yet.
This could have been a problem. Umbra waved gently. "Hey, am I in the way?"
"Not yet." He crossed his arms. "I'm replacing the teacher in third period."
That confirmed who he was. Would it work? She glanced up at her tiara, then back at the man. "You look a little tired."
"Nothing a little--" He paused to let out a big yawn into a raised hand. "coffee wouldn't fix." He would not make it to that coffee, at least not right away. Slumping against the door frame, he was busy passing out right there, sliding to the floor.
"Magic items, still work," gladly reported Umbra, to herself. Her magic didn't. She didn't have a horn, so that made sense. "You will feel like a thousand bucks, later." Her magic was not a cruel magic. She had put him in a deep and restorative slumber. It just wasn't an asked for naptime. "Shadow powers." She wriggled her fingers as she crept up on the sleeping man. "Time to..." She moved the snoozing man out of sight so she could teach that class without interruptions from people who were actually supposed to be there.
"Twilight!" She saw her moving past down the hallway.
Twilight stopped at being called, looking around. "Over here." Umbra waved a hand without the rest of the arm.
Twilight came up to the door to peer inside at Umbra, eyes going to her tiara with a gasp. "Umbra?"
"The one and only. Aw, you're so young and cute." She clasped her hands together on the desk she was seated behind. "Any luck finding your tiara?"
"Why are you so much older?" Twilight stepped in, eyeing Umbra with so much confusion. "I was an adult, but now..."
"Now you're a teen," completed Umbra. "You didn't know before? I was older than you back in pony land."
"This might be rude to ask." Twilight rubbed behind her own head. "But how much older? I'm a lousy judge of that."
Umbra considered as she steepled her fingers. "Well, I was already well into adulthood before I arrived in Equestria. This is why Equestria, as a whole, seems adorable. It's like living in a child's world, and I'm not complaining really. Minus the horrifying nightmare attacks, but even that isn't entirely off brand. Kids can dream up the nastiest things, given half a chance."
"I... see..." That Twilight saw seemed dubious at best. "That thief's name is Sunset Shimmer, by the way. Are you here to help?"
"Of course." Umbra fired a thumbs up. "Sunset Shimmer. A name helps a lot. I'll ask about her after I teach this class."
"You can teach? Your talents are more than I knew. I only knew you as a student." Twilight rubbed at her chin softly. "And now you're an adult, and I'm a child."
"An adorable child that I want to protect," firmly stated Umbra. "But if you mean professionally? No, but I'll wing it as best I can to keep up the disguise, then go chat with the other teachers, maybe learn more about this Miss Shimmer." A finger raised. "That is a super Equestrian name, but then, the principal is Celestia, so they probably all have Equestrian names. This is not Earth."
Twilight sent a brow up. "Earth?"
"Where I'm from. You should get moving. Third period is coming up and unless you want to go over trigonometry, you don't need to be here for that."
"Ooo, math?" Twilight looked a little too excited about that. "No, I should stay focused. We have to get that tiara back!" And off she went on her mission.
"Wait." Twilight looked back. "Where's Spike?"
Twilight's backpack suddenly jumped, the zipper undoing on its own and a canine head poking free. "Hey."
Umbra's eyes widened. "Oh, my, god... Oh! Wow..." She got up to her feet and came closer to the new Spike. "You are too adorable for words!" And soon she was scritching the good dog behind the ear. "Look at you!"
Spike looked conflicted, but the pets were too nice, winning out over any opposition to the treatment. "I'm helping Twilight."
"I bet you are." The scratching turned to gentle petting. "She's lucky to have you around. But why are you a dog?"
Twilight poked her elder. "Why are you an adult and I'm a filly?"
"Girl," corrected Umbra. "Huh, guess we all have different reflections through that mirror. Look, if you're worried, this changes nothing. We're on the same team. Think of me like an older sister, not some bossy adult."
Twilight suddenly went in for a hug. "Thank you. I really should get back to it though."
"Of course, both of you." Umbra started back for her desk. "Just be careful. I don't want either of you getting hurt."
Umbra grabbed some chalk and started making marks on the board in preparation. "Huh..." Clearly Twilight was seeing a very different side of the school they were in. "Wonder what her adventure is like." Hers was pretty calm, mostly, so far.
The bell rang through the school, many of them going off at the same time to announce one period ending. "Show time." Well, almost. Students would be coming. Umbra turned, placing her hands on the desk with her eyes on the door to see who would be the first through it.
"No way." The very first was a teen with bright yellow and red hair and a cocky smile. Sunset settled in a seat in the second row as other students poured in.
"Sub. Easy day." Sunset shrugged softly, clearly not expecting much. "What happened to Miss Angle?" She was not the only one with the question, other students muttering their own versions of it, more eyes upon Umbra.
Not that she shied from them. "Miss Angle couldn't make it today, so, lucky you, you get me!" She tapped the blackboard with the chalk she still had. "And we're going to go over just that, angles! I promise it won't be obtuse." One student chuckled, just one. Her joke was not a smash success, but she wasn't there to entertain them. "Let's begin."
Funny thing, as much as she had mentally groaned at the idea of doing a math class, it came back to her pretty quickly. She felt like she was actually reaching them, and teaching a little something.
One student raised her hand though. "Teach?"
"Umbra works fine," assured Umbra. "What's up?"
The student wriggled her fingers at Umbra. "Hi and stuff, but, don't most subs just give us busywork? You're... not."
It was true! Umbra was breaking the sacred compact of substitutes by actually giving a lesson. "Just because your teacher's not here doesn't mean you can't learn something. Besides, she left really good notes, so I could pick up where you left off. Good on her for doing that, or maybe I would have had to."
The reaction was a mix of understanding and groans at a break period that had been dashed by a well prepared teacher and a substitute willing to put in the work.