Sirens Headcanon: Part 1

Once upon a time, in the early days of Equestria, the seaponies that lived within the ocean surrounding it would regularly come to the shores and charm the onlookers. They sang songs that spread joy and happiness to all that listened. The seaponies did this for nothing in return, except to make their neighbors smile.
Among these creatures was a particularly beautiful seapony named Arianna. Singing was her passion, her life. Her songs attracted everypony to her, and she gained many suitors. She meant well, but soon many female ponies from the mainland became distrustful and jealous of her. One day Arianna sang to a stallion, not knowing he was engaged. When he fell in love with her, his fiance, a powerful but vengeful unicorn, not only broke off the engagement, but cursed the seapony- that her singing would not bring love, but feelings of hate and distrust, and that she would one day die at the hands of a loved one.
Distraught, Arianna vowed never to sing again, and distanced herself from both regular ponies and her fellow seaponies. Fearful of death, she wanted to avoid any personal, deep attachment from men. But society still expected her to marry, and she was torn between her expectations and fears.
One day, as part of a peace treaty between Equestrian Dragons and the Aquastrians, the Dragons asked for three brides- seapony brides to be exact, for three bachelor dragons. Arianna decided that this was the only way for her to not only avoid trouble, but marry without risking her life. And so she gave herself to Grayhorn, an older and somewhat sickly dragon who had a short amount of time left. She and two other seaponies, Lolita and Serena, moved permanently to the Equestrian shores to live on land with their dragon spouses. They were given the legs of ponies in order to survive on land, and lived only a few feet away from each other.
Lolita had a condition that made her appear younger than she really was, and so she had trouble finding a husband on her own before the truce. Fortunately her fiance Resonance was a rather understanding creature and respected her as a young woman rather than the child she appeared as. It would be some time before they truly found love together, though.
Serena had always been shy and had trouble finding love. She also hoped to join the Sect of Luna-she’d already been a devoted fan of the underwater division, which was small but planned to expand to the mainland. But her parents would not approve- and most potential suitors did not share the interest.Eventually she gave up the thought of having a soulmate, lest one who shared her devotion for the moon princess. So she offered herself to marriage with the stoic Lawclaw to pacify her family.
The three seaponies became friends and bonded over their fates, promising to support and protect each other.
Soon after the marriage, Grayhorn passed on, and some time afterwards, Arianna conceived a daughter. The girl was given the name Adagio, and she inherited her mother’s beauty. But being part dragon, she had more monstrous physical characteristics as well. Additionally, there was a beautiful yet mysterious red jewel embedded in her chest. But the real trouble began when Arianna found herself unable to feed the child. No regular food sustained her. Every day the baby would cry from hunger, but she refused everything her mother tried to give her. Then, one evening she heard a fight going on outside. Arianna ran outside, baby in tow, to stop the fight. As the ponies involved in the quarrel increased their anger towards each other, a mysterious green mist appeared. Only two creatures seemed to notice or care: Arianna and her child, whose jewel was glowing, and she was no longer crying. The young mother realized in horror that this was the only way her baby would survive- by feeding off negative energy.
And so once a day, she went outside with Adagio in her arms, and set free her gorgeous but venomous voice, singing to anypony who was outside. Eventually arguments and fights would break out, and the mist that sprung about made its way towards little Adagio’s jewel. Tears streamed down Arianna’s cheek as discord and animosity rose around her. But she was desperate to keep her child- the one thing she loved unconditionally in the world- alive.
Sometimes at night as Arianna rocked her baby to sleep, Adagio looked up at her with wide, open eyes, almost as if asking why she was only able to live off emotions. Arianna had no answer for her. She simply cradled her daughter, and hoped for a better future where Adagio could survive without the need of negativity, where she could be normal.
By the time Adagio was four, she’d figured out that she could manipulate her appearance to make herself resemble a pony, albeit with strange, translucent wings. Often she’d switch back and forth between this form and her natural, gold seahorse form- her mother noted that she resembled the horses of nearby countries than the average pony in Equestria. Not wanting her daughter to be shunned for her appearance, Arianna insisted she hide as a pony whenever mother and daughter went out in public.
Adagio, or Gigi, as her mother called her affectionately, had also managed to feed herself. Mother told her not to stir up trouble intentionally among ponies (they usually went out and searched for ponies already in heated discussions, and Arianna watched as Gigi absorbed the energy through her jewel.) But it was not enough for Gigi, who was almost always craving energy and power. She found her loophole eventually. Her singing voice, she and her mother found, had a strong influence on others, much like Arianna’s- only others would only fight if instrusted to do so, rather than merely being compelled. Mother said she couldn’t make ponies argue, but she’d said nothing about other creatures. Using her voice, she’d force bugs and other animals to fight and maim each other, and then sat back as she devoured their negative energy. She’d keep this a secret from her mother, of course. She was already making her hide her true self, and Gigi often wondered if Arianna thought she was a monster.
Meanwhile, neighbor Lolita and her dragon husband had their own child, who was a creature not unlike Gigi, except her body was a magenta color. Like Arianna before her, Lolita couldn’t figure out how to feed her child, and the baby cried endlessly. Lolita went to Gigi’s mother for help, who theorized reluctantly that her daughter would be sustained by absorbing negative energy. Arianna went out that night with Lolita and her baby girl, and she sang once more. Sure enough, the magenta child’s jewel glowed with energy when the others around them argued, save for her own mother and the perpetrator of the song. In gratitude, Lolita named her daughter after her savior- shortening it to Aria.
So now the new mother and child paid a visit to Arianna’s house once a day for feeding. The two seaponies discussed having their daughters play together, but Resonance figured that she might get along better with dragons. Arianna was also fearful of what the two not-quite seaponies might do without adult supervision. And so she kept Gigi up in her room when she fed Aria. But little Gigi was clever and curious, and often spied on her mother during this time, wondering what, precisely, her mother was hiding from her.
Arianna feed Lolita’s baby until the child was three. Around this time both Aria’s mother and father took her around for feeding her, and her dad often let her play with younger dragons. Meanwhile, Arianna kept Gigi hidden from public eye when it wasn’t necessary to feed her. Overtime Gigi grew angry at her mother. Why should she hide? Why was mom ashamed of her? Why couldn’t she find somepony else to play with? Though Arianna meant well, she was unknowingly causing her daughter stress and despair- and something much worse.
It wasn’t until Gigi was nine that she had a mind to go sneak off and spy on the dragons during their migration time. It was here that she met a kindred spirit in none other than Aria. Sharp-tongued and bad-tempered, she was one of the (dragon) boys, but she’d do. The two girls chatted and bonded over how different they felt from other seaponies. How anxious they were about how their parents truly felt about them. And though Aria had plenty of dragons- the few creatures who weren’t afraid of her- to play with, she never felt as though she had a true friend. Could Gigi be the BFF she always wanted?
From their first meeting onwards, the two were inseparable. Gigi taught Aria how to stir up conflict between animals, and they’d share their negativity feast with each other. Occasionally they’d go up to the dragon kids and fight with them,sometimes to feed, sometimes just for fun. And though Aria had stopped playing with them, favoring Gigi’s company, she never lost her “dragon” edge. If anything, it had increased- but perhaps in the worst way. Over time she became ruthless and cruel to other children, as did Gigi. They began to move onto provoking ponies and older dragons for energy. It wasn’t long before the two were using their singing voices to make others do as they wanted. At first, they used it to provoke more anger and hatred. Soon, they made them give the girls free food, toys, and at one point, even “boyfriends”.
Aria’s parents became concerned that Gigi had become a bad influence on their daughter, and tried to split them up. Aria was forbidden to go to her friend’s house, and Arianna, now made aware of Gigi’s cruelty, kept her locked in her room. Gigi had to get her energy by making others fight from outside her window.
As for Aria, she’d already begun to fall under her friend’s spell; her parents were her oppressors while Gigi was her savior. After all, she was the only creature who’d ever allowed her to be true to herself, and was willing to be her friend. For all she knew, Gigi might be the only friend she’d ever have.
In retaliation, Aria snuck over to Gigi’s house one evening after her parents fell asleep, and she spent the night in her friend’s room. Together they forged a plan to keep their parents distracted so they could be together. Gigi knew for a fact that her own mother had a crush on Aria’s dad. Perhaps they could work with that...