The words hung in the air between them for a long moment, and Sunset was beginning to think the human Celestia would turn her away.

“...does it always feel like this?” Celestia’s voice broke the heavy silence. “Magic, I mean?”

Sunset tilted her head a fraction, considering the question before answering. She could hear the myriad of things packed into the short query, all the things Celestia yearned to know yet could not bring herself to ask. Does magic always mean pain, was the real message, is it always a thing of suffering and cruelty? The former unicorn knew then that her hypothesis about the Sirens’ greater activities had been correct. “It depends on the magic and how it’s used. Dark magic though?” She sighed. “You feel slimy, gross...like you just swam through oily waters, and all of the dark thoughts are...just a little louder. You feel dirty and ashamed, guilty and weak and pathetic, and something inside you feels shredded and messed up...and you can’t help but feel like it’s all your fault.”

The older woman rubbed her face, and the redhead could see the cracks in her facade. “All that and more...I feel...like it’s still there. Like they are still there, in my head...are you sure whatever they did is gone?”

“We destroyed the source of their magic—they’re no more magical than your average human now, where ever they’ve run off to.” She paused, before offering, “I can check to see if there’s still any magic on you, if that would help?”

The principal looked surprised. “You can do that?”

“Sense magic? I learned how to do that a long time ago...” Sunset glanced out the window to the statue. “All the magic inside me didn’t just...disappear when I came through the portal. The Law of the Conservation of Energy applies to magical energy just as much as it does to any other kind. It’s just...humans aren’t meant to channel it—so it’s locked away most of the time, where I can’t access it. But that doesn’t mean I’ve forgotten anything I learned how to do, and sensing magic is...it’s an innate sense every unicorn has. I honed it during my studies, and because it requires almost no active magical use, its an ability I can still use freely.”

When she looked back, Principal Celestia was staring at her intently. “How does it work?” she asked, an almost desperate note in her voice.

“Um...well...basically I use the magic inside me as a sort of...primitive thaumometer. It reacts to external magical sources of energy in minute but detectable ways—kind of like competing electromagnetic fields? I’ve studied the way my magic reacts to all kinds of other magic in different concentrations and forms, and based on that knowledge I can...get a basic feel for whats around me. It’s not as precise as a number of active diagnostic or aural spells I know, but given that I can’t cast those here, it’s what I’ve got to work with.” Sunset rubbed the back of her neck. “I’m sorry, Principal Celestia. It’s hard to explain, especially because half the words I need don’t exist in any human language.”

“...so you have to have magic to sense magic?” The woman’s shoulders slumped. “Damn it all.”

Hearing the normally composed educator swear set off alarm bells in Sunset’s psyche. “Principal Celestia...what’s wrong? This is about more than you dealing with lingering residue from dark magic.” She opened her senses as she spoke, and while there were the barest hints in the office from the nasty energy the three emotiphages had wielded, Celestia herself was free of dark magic influence. Still, the woman’s agitation, shame, anger, and fear were written so plainly in every line of her body that Sunset could practically feel them, and it felt like the universe had broken a fundamental physical law as a result. “I can’t help if you don’t tell me. Please? It feels all wrong, seeing you like this. Princess or Principal, the Celestia I know doesn’t act this way. Please don’t let the Sirens win this way, not after how hard you fought them.”

It was unnerving to see Celestia so still, so small and seemingly broken. Her spirit and presence was so much like the sun her alicorn counterpart commanded, warm, unwavering, and larger than life. “What if I didn’t fight?” she bit out hoarsely. “Would your Princess have handed over those who trusted her...to things like that? Would she have just given up, let them do as they pleased? Watched as they tormented people who were her responsibility? Would she have been so damnably useless?!” Her voice cracked at the end, overloaded with pain and anger, and her eyes locked with Sunset’s, practically begging for the former unicorn to condemn her.

She could hear the echo of her own self recriminations, her own self loathing and anger at herself in Celestia’s words, and while it wasn’t the mare that raised her, it struck a painful chord in her soul. She stepped even closer, inside the principal’s personal space bubble and hugged her, the same way that the girls had hugged her earlier, the way Velvet had hugged her the other day. “You did what was necessary to protect as many as you could, just as she has done in the past. And whatever you might think, you didn’t give up—I saw you. Every time they tried to hurt me using you, you were fighting them, trying to let me know it wasn’t you saying and doing those things.”

“You weren’t useless—every ounce of energy and attention they had to use on controlling you was energy and attention away from the girls and Princess Twilight. It was energy they couldn’t use in the battle, energy they couldn’t use to bring more people under their thrall.” Magic tingled under Sunset’s skin, and without hesitation, she willed it to flow from her to the principal, wanting to replace the horrible sensation of the Siren’s magic with the way she thought of magic feeling: like heat and sunshine and fresh air and being gloriously alive.

Tension bled out of Celestia’s frame. “I still failed them,” she whispered. “I wasn’t strong enough. I couldn’t beat them.”

“None of us could, Tia. It was not just you.”

Sunset turned her head towards the door, where Luna had slipped in, carrying a grocery bag. The vice principal held it up. “I took up your suggestion of ice cream, Miss Shimmer. I hope that ‘Double Fudge Brownie’ is an acceptable flavor.” As she unpacked the carton, three bowls, and a some spoons, she continued speaking to her sister. “You were not the only one who could not succeed at shattering their mental shackles, sister. I suspect that most of our staff carries the same guilt—that they were incapable of breaking the hold on them from those three wretched monsters—I know I feel that same guilt.”

Releasing Celestia from the hug, Sunset faced both educators, expression serious. “I told you on Saturday, Miss Luna, and I meant it: the Sirens were an ancient and powerful enemy from Equestria. They’ve been alive for thousands of years—on both sides of the portal—and one of the most powerful unicorn sorcerers in all of recorded pony history could not beat them. That’s how they ended up in this world to begin with.”

“And yet, seven teenage girls did beat them,” Celestia pointed out bitterly. “Six of whom are my responsibility. Children who have no business being in danger, and yet twice now they have done what I failed at.”

The unicorn-turned-girl ran fingers through her fiery hair. “Okay. I...think I need to explain a few things.” She took a deep breath. “The girls aren’t just ordinary girls anymore, and Princess Twilight and I never were. Princess Twilight is an alicorn, just like Princess Celestia...and before she earned her Ascension, she was one of the most powerful unicorns of a generation, just like I was before I ran away.”

She exhaled, accepting a bowl of the ice cream from Luna but held off on eating until she finished explaining. “Not only that, but Twilight is the current Bearer of the Element of Magic, one of the six Elements of Harmony. In my world, the Elements of Harmony are among the most powerful, most ancient magical artifacts known, and the magic they create has the power to cleanse and heal even the greatest of evils. It was the Element of Magic that was set in Princess Twilight’s Crown, the one I stole. That was the Crown that turned me into a demon, and it was the Element of Magic that empowered the girls—who I suspect are the human counterparts to the current Bearers of the Elements in Equestria. The magic from the formal? The Rainbow of Light that changed me back? That’s the Elements at work, and magic like that... it leaves some of itself behind. I can’t explain it any better, because I’m still trying to figure out how it works here, but the girls are touched by the Elements. They have a leg up against any magic from this world or Equestria.”

Luna whistled. “That...sounds most impressive...though it does not explain your immunity, Miss Shimmer. Was your cleansing at the hands of your friends enough exposure to these Elements to protect you as well? Or does that come from being a unicorn?”

Blue-green eyes squeezed shut. “I don’t think so. I think...I think I was rendered immune because I turned into a demon...when it comes to dark magic...demons are the most dangerous of dark magic entities...especially ones like I became. Even Princess Celestia would exercise caution against anypony who became so twisted by their emotions and powerful magic that it transfigured them into a demon. The Elements may have cleansed me, but my reaction to the Sirens’ magic says I still carry the scars.”

Shaking herself, Sunset redirected the conversation to the important points. “What matters is that it wasn’t seven teenagers that fought them. It was the Elements of Harmony and...whatever magic I’ve managed to access here...and we almost lost. The Sirens had more power than you think.”

“Then how do we stop this from happening again?” Celestia’s frustration was evident in her voice. “We cannot simply rely on you girls and a magical pony princess on the other side of a somewhat unreliable gateway to wage war against every supernatural force that shows up here with plans of domination or worse! There has to be some way to defend ourselves or at least gain enough warning to get people to safety!”

“Or a way to fight back,” Luna interjected firmly. “I for one am done being a doormat for magic and monsters. They want me, then they had best better be willing to lose limbs. I will not go quietly!”

Amber fingers tapped the spoon against the side of the bowl, Sunset’s thoughts turning inward as she considered what she could offer the administrators. All things considered, she felt as though the knowledge that she and her friends were going to train their magic would not be enough. It was, however, a good starting point. “The girls and I are already making plans to learn and study how our magic works in this world, so that next time we aren’t left scrambling for a week while our enemy tramples over the people around us. I also spent some time talking to Princess Twilight before she went back to Equestria. She and I are going to be working on research together, and she’s promised me that she can send over books and other resources that I need. In addition to material for my research, I could ask for some material on defensive methods...” A sudden idea sparked. “In fact, I think I even know the ones to ask for that could be easily translated for use by humans—there’s a fair bit of anatomical similarities between humans and minotaurs, and most minotaurs are...well...the exact opposite of magically inclined, so most of their defensive arts rely on mental and physical training instead.”

Luna grinned with a bit more savage satisfaction than Sunset expected from her vice-principal. “Do these minotaurs have mental techniques to keep one’s mind free of magical manipulations?”

Brows furrowing, Sunset tried to remember what she had learned from the Solar Princess in the year that the minotaur delegation had come to renew their treaty with Equestria. “Very likely. Minotaurs value both physical and mental fortitude, particularly when applied to difficult tasks. I can have the princess look?”

“Please do so. I cannot realize my teenage fantasy of being ‘Luna the Vampire Slayer’ if I become bedazzled by every low end piece of magic trash that comes to the school.” Celestia gave her sister a look, causing the dark haired woman to roll her eyes. “It was a joke, sister. Allow me my coping mechanisms.”

Celestia rubbed her face. “I’m sorry...I just feel like there has to be a way other than relying on you and your friends, Sunset. Some other answer.” She gave her sister another pointed look. “One that doesn’t turn my staff into weapon toting vigilantes, or put my students in harm’s way.” She tapped her fingers on her desk, ignoring the bowl of ice cream Luna had set before her. “Some manner of detection or early warning system maybe? Or some kind of magic deterrent that keeps them from coming on campus in the first place?”

Sunset’s mind raced, considering ideas at a rapid pace. “I...can’t promise anything, but I have a few avenues of research I’d like to try exploring, and I would wager Princess Twilight has some ideas too. I can add some form of magic detection system to the list.” She took a deep breath. “That’s...where I wanted to...ask a favor.” She dropped her eyes to her ice cream, trying not to squirm under the scrutiny from the administrators.

“We know the magic comes out when we play music, and all six of us have a free period before lunch. It would help if we have a permanent place where we can practice and store our instruments—I don’t want us to be taking the music room away from other students all the time, and it would give me a place to conduct research too.”

Celestia steepled her fingers, agitation calming significantly, and Sunset realized she’d inadvertently stumbled on a solution to help combat the Principal’s frustration and feelings of uselessness. “That...that is something I know we can help with. Luna? The old A/V room on the second floor—we’re still using it for storage for all of that outdated technology from the library, correct?”

The dark haired woman snorted. “And then some. Please tell me you are presenting me the opportunity to finally dispose of all of those overhead projectors and microfiche machines? Not to mention that oversized paper weight that was outdated when you were a student, sister—I am fairly certain no one attending the school has ever even heard of a ‘ditto’ being anything other than a Pokémon.”

The sigh that escaped the principal was the same kind Sunset had heard come from Rarity when she described Sweetie Belle’s latest disaster. “Yes, Luna. It’s been long enough—go ahead and take all of them out of the system. Raven knows which forms you’ll need. Keep at least one projector and a single microfiche reader—they can go in the actual storeroom.”

Luna restrained herself—barely—to a fast walk, humming a tune under her breath, leaving Sunset alone with Celestia once more. The woman turned her attention back to the former unicorn. “You girls can make the old A/V room yours. It's right next to the music room, and like it, has significant sound proofing. There’s a desk in there, and a few empty book cases you can feel free to make use of, and the door has a key.” Tired eyes attempted to give Sunset a stern look, but there was no force behind it. “You’ve done a great deal to show us a much better Sunset Shimmer, one who has all the makings of a great leader and formidable woman. You understand what kind of trust I’m placing in you and your friends with this, don’t you?”

“Yes ma’am,” the redhead answered, intensely serious. “I promise you, I won’t let you down.”

“I trust you won’t, just as I trust that the six of you will not abuse the privileges that come with the rest of what I have to say.” Celestia continued to hold Sunset’s gaze. “Within reason, I’m willing to make resources available to you in the pursuit of finding ways to protect the school and those within it—for example, as an educational facility, we can request library loans of books and research materials that are impossible for a teenage girl. This extends to other areas such as materials and supplies, that again, would be difficult for a teenager to have access to purchasing. This does not mean it will be carte blanche on anything you suggest acquiring—I have to still discuss it with the teachers, but likely, any requests for materials you have will go through Luna or myself. Do you understand?”

“I do, Principal Celestia,” Sunset hastened to assure her. “As…for materials…I might need access to electronic components—there’s some preliminary implications that large bursts of magic interfere with electronic devices, but I’d have to experiment to learn how that works before I could even hope to come up with something that might work as a detector. In the interim, I was actually thinking about talking to Princess Twilight about some more common spellcrafting and arcanotech materials from Equestria. This world just does not have any good spell-quality gemstones, especially not ones large enough for any decent sized spell matrix.”

The former student of Princess Celestia straightened her spine, standing tall, determination strengthening her resolve. “I will do everything in my power to make sure that if and when the next magical threat shows up, there won’t be a repeat of what happened last week. We’ll be ready—all of us.”

Sunset's ability to sense magic is never fully explained, but it does crop up in canon several times, and she even calls it out directly in Legend of Everfree. This is my take on it.

Also, yes, I do follow the Gargoyle's adage: "Energy is energy, be it science or sorcery."

A note on the language, since my editor and I mused over this...the idea I go with is that the common tongue of Equestria and the "American English" used in human land are a close match for similar reasons: both languages are not an original language, but actually an amalgamation of a handful of base languages with influences from a bunch of other languages, and when you pair this with the "parallels between worlds" you come out with something that, on the surface, is functionally similar enough that Sunset or Princess Twilight can still understand the local tongue. However, at the same time, all of the idioms, figures of speech, any and all jargon for both magic and high end tech, anything that requires a specific historical event or context as a "turn of phrase", etc...those are lacking. So Sunset can manage to speak human, but there are just things she's not going to understand until taught, and more than that, if she started using the words her kind use for high end magic, humans would likely hear naught but gibberish, nonsensical words like one finds in Dr. Seuss.

....Yup. Obligatory Buffy reference. Its a bunch of high schoolers fighting magic and mayhem. Cmoooooon. Besides, we all know Luna was a fan of the show.