Warning: I've come up with a lot of possible backstories for the sirens, and this is the second or third darkest one. Enjoy, I guess?
Adagio paced into Canterlot High's music room with more trepidation than she'd have liked to admit, closely followed by Sunset, who gently shut the door.
"Okay, the room is sound-proofed, I checked for anything that could feasibly be used as a listening device three times before coming to get you, during which I locked the door and am the only one with a key, I've locked the door again, the curtains are drawn shut so no one could be reading our lips even if they could see into second-floor windows, and-" she took one quick look around the room just to be sure, "-we're totally alone. No one but me will hear anything you say." That was everything Sunset could think of to ensure privacy, but Adagio's guarded stance, the way she lightly hunched over with crossed arms and a shaky smile on her face, said it wasn't enough to put her at ease.
"Heh. To think you already have such a thing ready. Do you use this room often?"
Knowing that Adagio was just nervous, Sunset didn't let the implications of the question get to her. Instead, she sat down on the rectangular... cushion, thing, and patted the spot next to her.
"You even have a soft surface prepared," she muttered as she took her seat, "how suspicious." When Sunset didn't protest or even make any flustered noises, she had to look at her. That she wasn't blushing at all said the joke probably had no basis in truth. She sighed. "Sorry, I've, never had to... Not even Aria and Sonata know some of this, and if they ever heard..." Her mouth worked in vain for a few seconds as she tried to find the right wording, but Sunset pulled it off a little faster.
"Would it help if I formally promised not to tell anyone else? Pinkie Promised, even?" Adagio's bewildered look drew a giggle, so she pantomimed the motions with the words. "Cross my heart and hope to fly, stick a cupcake in my eye."
"The idea is that no one breaks a Pinkie Promise, because doing so is the surest way to make friends stop trusting each other. In essence, it's the same as any other promise, but I guess the special name and rhyme give it a little more gravitas. Or, it does for anyone who's friends with Pinkie anyway."
"Cross my heart and... hope to fly?"
"Stick a cupcake... I could swear it was needl-"
"In Pinkinese, it's cupcakes."
"Very well. Cross my heart and hope to fly, stick a cupcake in my eye. Those are the words for an important promise?" She chuckled as Sunset nodded. "Well, that doesn't really sound much less painful than a needle."
"Depends on whether or not there are sprinkles."
"...I would ask, but I think I have a story of my own to share first."
"Try it yourself; Pinkie Promise to share the story, then tell me, and I'll do the same with not telling anyone else."
Sunset led as they said the words and performed the motions together. To Sunset's great delight, Adagio was smiling too, even if only in a slightly self-conscious kind of way. They sat in silence for a few minutes as Adagio got her thoughts together, her will to make good on what she agreed to in Celestia's office bolstered by the Friendship-Packed Power of the Pinkie Promise. Just the same, she began very, very quietly, eyes glued to the floor.
"I could worm my way out of this if I really wanted to, you know. Evasion was one of the first things I learned."
Sunset kept her voice gentle too. "Learned from whom?"
"My keepers. I don't know if I was bred in a lab, spawned in a pit, or taken off the streets as an infant, but my earliest memories are of the facilities. They called it The Hadal Zone, after the deepest, darkest oceanic tren-" She accidentally startled Sunset by quickly turning to look at her. "You already knew that, I would bet."
"Eh... The, trenches part? It's not a field of expertise for me, but I'm familiar, yea."
Adagio nodded, looking at a distant wall now. "Right, right, that might save time somewhere. So I don't need to explain that the dark, crushing depth of the thing paralleled the operations performed inside, and how much the rest of the city above knew about it? I spent my first few years in a cluster of stone cells, learned everything; language, math, history, magic, and so on from a few different types of projectors. I was given food if I did well, but I was always 'fed' streams of negative energy regardless, the power accelerating my growth, both mental and physical." She chuckled at the memory of those spires hanging down from the ceiling of the main room, crackling with red light at virtually all times. "I used to scream during those forced feedings, at least until I was what amounted to a little girl, but no matter how much it hurt, I always wanted more."
"The... th-the, w-wait, I thought...?" Adagio looked directly at her again, one eyebrow raised. "I thought you guys fed on negative energy when we first saw you, with the gems. Did you just need them so it wouldn't hurt?" Adagio's face shifted as though Sunset were a painter asking what a brush was.
"It's negative energy, Sunset Shimmer. It always hurts. Do you not recall?"
She did. Very well. "Yea, but, I thought that was just because I was using the Element of Magic wrong." Then two realizations kicked in, each making her heart sink a little lower. "So, Twilight felt the same thing? And, you guys got another dose of that every time you absorbed energy?"
"So ponies don't teach anything about dark magic, interesting..."
"You were practically tortured since infancy?!" Sunset wasn't sure what it meant that as hesitant as Adagio was in sharing this story, this apparently wasn't the reason.
"It really wasn't as bad as it sounds, and at that age, feeling that power was, well... imagine a sugar rush that bestows actual strength."
"And horrible, searing pain?"
Adagio shrugged. "All living things capable of feeling discomfort experience some amount of pain in their daily lives, Sunset Shimmer, but not all are so fortunate as to feel the power surge like we did."
At a loss for words, Sunset stared at her for a long moment, then let her head fall to her hands. "...Before we go any further, who did this to you? And, why? Did they do it to the others, too?"
"We're getting to that, but no, as far as I'm aware, Aria and Sonata lived fairly normal lives until they met me." She'd been sure she would cry when she finally said those words out loud, thinking of everything she'd inadvertently taken from them just from approaching after Aria's performance to say hello, but she was feeling surprisingly stable right now. The hard part was still coming, so she rode the momentum while it lasted. "As said, I was taught more than school subjects. Marechiavelli was long before your time, but...?"
Sunset looked up, the tiny scholar in the back of her head doing a giddy dance as it remembered she was speaking to a (technically) ancient being. "Underhanded, manipulative means to keep one's nation running? I'm familiar."
"Imagine that, taken to far more ruthless extremes, not for the preservation of a state, but for oneself, encouraging the spread of hatred and chaos at every turn, and generally being the kind of utterly remorseless, self-serving megalomaniac that might try to, say, brainwash a population to lavish her forever."
Smiling hopefully, Sunset tilted her head a little. "Yet, willing to apologize for threats and teasing, and to make promises with silly rhymes to make up for them?" She smiled wider as Adagio blushed, a bashful little grin working its way across her face as she looked away.
"...I didn't say they were completely successful." Though she felt herself get even warmer, she only locked up for a second when she was hugged this time. When Sunset released her, she went on. "That said, they did a good enough job that I was able to bear the master gem they'd been crafting in another part of the facility, for which they needed-"
"A conduit," answered Sunset, "someone already aligned with the negative energy at the kind of intensity they made sure you, their subject, could handle, then use when the time came?" This won a bright, maybe even admiring smile out of Adagio, but Sunset wasn't nearly as happy herself. "They used you like a..." She shook her head in equal parts disgust and disbelief. "A tool, a machine, a piece of equipment?"
"It went a little further than that."
Adagio turned her head away again. "W-when I was a young teen (you know, give or take), I riddled out a way to escape The Hadal Zone, laying eyes on the open sea for the first time. It was blue, like in the pictures I'd seen. Somehow, I'd expected it to be green like the walls in my cells, but it wasn't."
Noting the abrupt change, Sunset opted to just let her go on.
"I had spent the last few years beforehand believing that everything in the cells was mine, because that was my whole world up until that moment and there was no one to challenge me for its dominion. With one look around, I immediately decided 'And now all of this is mine.' I saw the researchers, the kelpies who raised me from behind screens and through speakers, floating nearby. It was the first time I had ever laid eyes on another living thing in person, and since I knew they had already given me everything I had, I determined that they would give me more or I would take it, by any means necessary. I swam straight up to them, the four kelpies whose grasp I'd just slipped out of, and told them I was ready for more. I don't know if they meant for me to try to get out that day, but they considered the whole thing a sign of overwhelming success."
Sunset didn't say anything out loud this time. They wanted their little monster, and I guess they got it. God, I hope she went Mewtwo on them.
"Part of my instruction was watching recordings of normal interactions, simulating normal conversations, roleplaying exercises as a regular kelpie, and getting a feel for how to interact with others so I wouldn't be a complete fish out of water -no pun intended- when it was time to interact with society at large. I learned the rules, studied normal behaviors (which, as you might have guessed, didn't do me as much good in this civilization), and integrated with little difficulty, passing for a normal kelpie and attending a regular educational system more to pose as an average citizen than to actually learn anything."
"You said you were a B student before."
"The lack of negative energy spires in normal classrooms wasn't exactly motivating."
"It was during this undercover period (which, I would later learn, was essentially just to keep me occupied) that I met Aria and Sonata for the first time. They were average kelpies, the sort I'd considered entirely beneath my notice until I happened across Aria performing at a musical showcase. What did you think of her song, by the way?"
Sunset smiled. "Uplifting, but with a bit of a punch, like a musical uppercut." She smiled wider as Adagio snorted with amusement.
"Yes, I suppose that fits. It was that 'uppercut' that first got my attention, and... suppose I've been looking forward to the next hit ever since. I approached her after the show, where her proud posturing over first place drowned out the sounds of Sonata's sentiments that she'd beat her next time. Long story short, I wormed my way into Aria's head through a carefully-measured mix of subtle promises of power and greatness, bending Sonata (her only friend at the time, believe it or not) to serve me through demonstrations of the power I was offering Aria, hints that Sonata would be the only one getting any of it (I wish you could have seen the adorable way Aria's snout wrinkled and her fins twitched when I said this), and fleeting, passive strokes to her ego to ensure she kept listening."
Sunset tilted her head. "You just, roped them both into working for you because you liked Aria's singing?"
"Not exactly. I had been urged by the researchers from The Hadal Zone to find minions, you see, living extensions of my will to hold and channel even more power than I could all alone. Sonata joining in earnest was something of an accident, but she took orders well, her voice balanced very nicely with Aria's, and..."
Leaning over a little as Adagio trailed off, Sunset found a faraway look on her face. "And...?"
"...I don't know," she uttered, "I just... I can't remember a good reason in line with what I'd been taught, but I liked being around her. She was funny, made me laugh, and the rest was something I justified later. ...It was the same with Aria; I heard her song, enjoyed listening to it, talked to her for a while, decided I wanted her with me, and any tactical advantage the duo had to offer was worked out after the fact." She chuckled, wearing a distant smile as she thought back. "I was supposed to find ideal holders of negative energy; those whose spirits were already aligned to hatred, malice, resentment, or even misery and sorrow, then dominate their minds, break their wills, and bring them back to The Hadal Zone with me. Instead, I picked those two, and subtly challenged my keepers to so much as question my choices. They didn't, but maybe it wouldn't have really mattered anyway."
Seeing the way her lip twitched, Sunset guessed that they were getting to the painful part. She didn't say anything, but she smiled hopefully when her hand being gently placed on Adagio's shoulder was returned with the fingers of Adagio's opposite arm lightly coming to rest over hers.
"...When I, when I brought the two of them back, I learned a little about the other project my keepers had been working on... Three gems. There were going to be more, but they ran out of funding. Not that it mattered. They had been working on those gems since before I was even bor-... whatever I was. The gems granted us the power you remember at much greater magnitude before we were abandoned here, but what had been k-kept hidden from me was that they were meant for control of their bearers just as much as the bearers' victims." She heard Sunset let out a quiet gasp, so maybe she could see where this was going. "When those stones were grafted into our flesh, they carried more than just the expanded magical capacity, but a-... You are familiar with computer technology?"
"Think of a program made to take control of a system, and, I suppose, a central unit to ensure that control program kept working. With use of a machine I had never known about, what we would do to those we sang to from then on, the gems were already doing to us." She was startled by what could only be called a glomp from a teary-eyed Sunset. "I'm not at the bad part yet!"
"That only makes me want to hug harder!"
Squirming in place for a moment, Adagio found that either she suddenly didn't have the strength to shake Sunset off... or couldn't will herself to. The thought that she'd been wanting this on some level sapped what little of her resistance had remained as she leaned into her comforter.
"...So... The gems did to us what we did to others. The d-difference? With my conditioning to negative energy, I retained my mind. Through everything." Sunset squeezed a little harder, but Adagio wasn't sure if what she heard was a gasp or a sob as she felt a lump form in her own throat. "You already know how the gems were used, how we could twist a crowd of listeners with our voices. Imagine that power amplified not just by the presence of a world already laden with magic, but backed up by an effectively limitless supply of negative energy for the time in which it was used. The coup was bloody, those that found any means of resistance in time were hunted down and killed by thousands of enslaved thralls, but they had us, and consequently all of Coltlantis, under their complete control within a week. They couldn't maintain that control over the entire population forever, but establishing their own little police state was easy enough. They had the necessary... let's say, paperwork, sorted out weeks in advance. The kelpies that were once researchers were now kings. Kings that grew bored once everything was theirs, quickly descending into debauched warlords for whom nothing, no one, was off the table."
The lump grew, but she wasn't sure if it was due to the memories or the little sounds that told her Sunset was unmistakably crying now. She tried to open her mouth to quickly finish the tale, but all that escaped was a sob. Before she knew it, she was the one crying in Sunset's arms, even as she felt teardrops on her shoulder. It was like she was bleeding, like she had a gushing wound that just kept flowing, wringing every drop it could from deep in her chest. Trapped in a very warm, tender embrace, she found herself simultaneously helpless, yet secure, perfectly safe even at her most vulnerable. That was how she remained until she had nothing left.
"They u-used all three of us," she stammered out under her breath, "f-for y-y-"
"Stop," Sunset all but begged, "I get it, you can stop now."
The silence lingered as Adagio considered the opening she'd been given, but she shook her head. "No." She swallowed. "Not done."
Not letting Adagio out of her grip, Sunset steeled herself. It was a little worse than she'd anticipated, but in this context, she was definitely glad she hadn't taken Adagio's first apology offer now.
"...They used us for years. It wasn't daily, and somet-times we were left alone for whole weeks at a time, but... I don't know how m-many times I saw Aria and Sonata staring back at me, oblivious smiles on their faces and no trace of comprehension in their eyes, even during the act when we were called together. A-and then," she hissed through a bitter laugh, "one of our keepers slipped up."
Thinking back to that long-awaited day, Adagio managed to smile. "As with our own victims, we weren't utterly dependent on continuous orders, had enough will to live our lives when not heeding commands. I had managed to keep secret that I wasn't fully dominated, and one day, one of them decides he wants to take me in the room with the central control mechanisms, one they'd kept everyone out of just in case something should go wrong with the equipment. I suppose he'd grown bored with the throne room and the city plaza, maybe just wanted to lay me over something new. He was so trusting, so sure his head wouldn't be anywhere near those gears..." Sunset, the spoilsport, said it for her in a whisper.
"You killed him."
"In the throes of passion, he got careless, didn't see where he was, and even told me to go faster. All it took was one good shove. I didn't have to wait long until another came to check on the machine. And, control on me being dampened with the damage to the central system, I didn't have to come when he called. He became part of the problem. Even as my senses returned to me in full, I couldn't see or hear anything that didn't involve revenge, unaware of what was happening through the rest of the city as I hunted down the last two in their homes. Control over governing forces broken, the city descended into chaos, and as just about everyone remembered our part in their subjugation..."
Sunset nodded a little. "Aria said something about you guys not being welcomed there anyway."
"I gathered the others and, with the source of that nigh-limitless power essentially destroyed during my vengeful rampage (which I hope clears up why I didn't come after your group after the Battle, by the way), we fled the city together, gems still stuck in our chests."
There was a long silence, broken when Adagio pulled back enough to look Sunset in the eye. "Well?"
At a loss for words after hearing that, Sunset took advice Rainbow had given her once and just went for it. "I, I-I can't even begin to imagine what that must have been like, trapped under someone's control, th-the things they did to-"
"Not that," Adagio said with a slow head-shake, her eyes cold and hollow. "the other part. I killed those kelpies. Even when, with the last three, I could have just brainwashed them once I was free again, I chose to kill. I'm a murderer."
They held one another's gazes for a long time, Adagio wearing a look Sunset knew she'd made a hundred times herself; one waiting for scorn, judgement, resentment, hatred, a confirmation that the one she was looking at was disgusted just talking to her. Eventually, Sunset sighed.
"I can't pretend I'm okay with killing, but for one thing? I'm having a really hard time feeling any sympathy for deranged, megalomaniacal serial-rapists." Seeing Adagio's eyes moisten again, she wasn't sure if this was the right thing to say.
"But killing them didn't accomplish anything! If I had controlled myself and enthralled them, I could have taken the reigns and had them fix the machine, used its control to slowly, carefully return Coltlantis to the way it was before! I couldn't have undone the suffering wrought by the kings, but I could have helped make things better rather than going feral, destroying the only means of keeping order, letting riots break out, and taking advantage of the chaos in the name of my personal revenge! When I had calmed down enough to assess the situation and go get Aria and Sonata, we left the city in turmoil. A-and, you told us...?"
Swallowing, Sunset nodded. "The survivors are said to have done their best to recover, reform the government and infrastructure, but the combination of damage to the bureaucracy under the kings, ensuing mistrust for magic, long-standing enemies of the state that had only been held at bay while Coltlantis was still a formidable force, and oceanic predators eventually overwhelmed them. It's not much more than a memory now." Seeing Adagio clench her teeth as she choked down a sob, Sunset had an idea. "But, if you're feeling like all of that is your fault, look at it like this: In the frame of mind you were in right after finally breaking their control, along with your... conditioning in The Hadal Zone, do you really think you'd have turned out much different from the kings?"
"Yes," Adagio snapped, making Sunset flinch, "I'd have never forced anyone to pleasure me, and it's something I never did, never let Aria or Sonata do, even when we had free reign!"
"Okay," Sunset said placatingly, "and what about the rest?" To her relief, Adagio looked much less offended at this, staring back at her in mild confusion. "I mean, it's easy to look back and say what you could have done in hindsight, but if you were anything like you were when we first met, doesn't it seem more likely that you'd have just taken over and ruled Coltlantis yourself, had the machinery not been destroyed?"
She gave Adagio the minutes she needed to process this, visibly exploring her memories of the time. Eventually, Adagio loosed a short, bitter laugh.
"You're saying that I'd have made things worse no matter what."
Sunset frowned. "That's not what I mean. I'm saying that with things how they were, with how you were brought up, there was nothing you-... With what you'd been through, what you'd been raised to do, expecting that kind of benevolence out of nowhere is asking a lot, don't you think?"
Adagio's mouth moved in vain for a few seconds. "...I still shouldn't have killed them."
Leaning over a little, Sunset gently rubbed a hand along Adagio's back. "Do you ever regret it?"
Tears slid down her face. "Yes." She immediately covered her face with both hands, but as Sunset gently embraced her again, she didn't feel vulnerable in doing so. Distantly, she noted that there was much more than just the shoulder-touch gesture to be mastered if she ever needed to do this for someone herself. "I-I still despise them," she eventually sniffled, "but, the feeling when I was going after them, that savage, unbridled hate, it-"
"Felt like you were being smothered from the inside," Sunset continued for her, "like thick, black sludge was clogging up your internal organs, practically numbing your body, your thoughts fading out, and all you could see were the ones you hated, how you wanted nothing in the world more than making sure they never saw another day?" When Adagio looked at her in surprise, she smiled regretfully, feeling a lump form in her throat as she thought back to the day she nearly killed the girls that were now her closest friends. "Even if I didn't get as far, I know what it's like."
She was startled when Adagio's arms reached up to seize her, but it was only to hug her back. They stayed that way for a while, gently holding one another in silence. It took much longer for Adagio to feel the same little sense of self-conscious revulsion she'd felt the first time Sunset hugged her, but she took the return of that feeling to mean that she was feeling... better? That was how this worked, right? Either way, she gently pulled back.
"As I said before, Aria and Sonata don't remember all of the details, a-and I know it's not exactly 'Honest' to keep something like that secret from them, but-"
Sunset smiled. "Even if I hadn't Pinkie-Promised to keep it to myself, they could probably do without being told exactly what happened to them, and if they ever do remember because of me, you'll turn me inside out?"
Blinking once, Adagio surprised herself with a chuckle. "No. I feel... a little better about this, actually, and I meant what I said about murder, but if those those two ever learn what happened and I can't comfort them? At worst, the guilty might never walk or chew food again."
"Haha, n-noted..." She now had one extra reason to be glad those two were accepted to Crystal Prep.
"Luckily, if a hundred years of experiences haven't dug anything up, I'm fairly certain they just don't have any memory of the period."
"I guess. So, is that the whole story?"
"Basically. Was there anything else you wanted to know?"
"Umm... In the song you guys played when you came back, Sonata said you guys took on dark magic for a boost, so does she know it was forced on you, or...?"
"The way those two think it happened, we were taken into the Hadal Zone, implanted with the gems, made their perfectly willing enforcers for the better part of a decade, and took a temporary hit to our cognition when the machine 'mysteriously malfunctioned,' costing us a chunk of memories relating to the time in which we were hooked up. Helps that when I found them, they were both badly disoriented, same as the kelpies under constant control that made up the police force."
"They didn't question how you would know that when you were hooked up too?"
Haughtily brushing her hair aside, Adagio smirked. "Sonata, thinking quite highly of me even back then, posited that I must have held together because I was 'so much smarter' than them. Regardless of how true you might consider that, Aria was more worried about our next move and they haven't questioned it since."
"Good thing, I guess... And, the 'starving' talk?"
"Feeding on negative energy was an option, but it worked more like drinking coffee. Black, burning coffee. It wasn't a replacement for actual food and rest, and it could certainly keep us going for a while, but the idea that we fed solely on that was a lie."
"People not liking your songs?"
"Well... We did vaguely try going straight once we left the sea (I was still feeling spiteful and the kings had soured me on my lessons just a little), but the first non-oceanic civilization we visited was a workaholic earth-pony town, one that hadn't really absorbed the message of a unified Equestria yet."
"Was this before the Windigos and the first Hearths Warming?"
"Singing was deemed 'not real work' by local important ponies (chief farmers and business ponies), no matter how much our listeners enjoyed it or how even non-magical tunes could make their work go by faster, and we were eventually driven away by a crowd of ponies throwing things. Granted, it wasn't directly at us, they were at least kind enough to miss on purpose. Even so, with that experience in mind, all bets were off and we were all about ourselves from then on." She chuckled. "I suppose there was a smidgeon of truth to Sonata's 'losing hands/bad luck' line, but it certainly hasn't been all bad."
Sunset felt her heart skip a beat as Adagio gently grasped her hand.
"Because if it were," Adagio continued, a warm little smile lighting her face, "we'd have never met you."
Her entire face burned. "I-y-yea, I, the, we, g-good, for, um..." She took a quick breath to get her thoughts together as Adagio giggled at her. "So, uh... th-thank you for telling me all this, I feel like I've got a pretty good sense of where you guys come from now."
Standing up, Adagio nodded proudly. "I Pinkie-Promised, did I not?" She gave Sunset a scrutinizing look. "...I mean, didn't I...?" Even with the amused look on Sunset's face, the affirmative nod made her smile again. "Right! So... I'll see you around?"
Getting to her feet, Sunset smiled too as the two of them moved for the door. "Yup! You're sure you're okay with being captain of CHS's cheer squad? We don't know how many people might join."
"If Aria and Sonata are going to be at Crystal Prep during the school day, I could use something to keep me occupied. Besides," she said with a growing smirk, "as I'm to be the one instructing CHS's prospective cheerleaders, Principal Celestia let me set the standards for entry."
A note of worry in her voice, Sunset raised an eyebrow. "'Standards'...?"
Adagio beamed. "First requirement: Completed Sex Ed class!"