As she journeys through the city with her friends, one by one, Siren faces the Elements of Harmony. Fluttershy is the corruption of Kindness, in the form of smothering control and materialism. Applejack is the corruption of Honesty, in the form of denial. Rainbow Dash is the corruption of loyalty in the form of fascism and blind obedience to leaders who don’t deserve it. Pinkie Pie is the corruption of laughter, and we’ve already seen why. Zephyr was one of Pinkie Pie’s followers, the teenage prostitute who always keeps a smile on her face even as she’s crying inside. Never stop smiling.

Soon, of course, Siren starts to suspect that Twilight isn’t dead. She can see where this is going. Because, in this big laugh Poison Joke is having at the city’s expense, it’s obvious what role Twilight plays. She’s the corruption of magic, because she did bring everypony else together in this strange and magnificent way that’s impossible to describe. But she didn’t make them happy. By her actions, their suffering brought them together.

Siren has her own worries as well however. As the powers Heart’s Desire grants her increasingly start to resemble Rarity’s, Green suspects that maybe Siren is still Rarity’s heir, and their once close friendly rapidly cools despite Siren’s best efforts. She still doesn’t know why Trixie is so determined to help her, or what plans of her own Berry has. It all comes to a head when she finally gets her hooves on the report Doctor Stable made, all the way back in the start of the story, when he was testing for her identity.

Siren’s blood, compared to a hair sample provided by Trixie. 99% chance of a maternal relationship. Echo knew all along (since he got the report from Rarity’s goons) and has been giggling all the while as Siren plays up her theatrics. Half a showmare indeed.

As the situation in the city rapidly degrades, with the Elements of Harmony united against Trixie and Siren, it increasingly seems that even Neptune’s Bounty may no longer be safe. Realizing this might be her last chance to set things right, Siren returns to Trixie’s lair.

Passing the young mare in the office -- who is revealed to be a wiredoll under an illusion spell -- Siren finds the real Trixie behind a sliding panel in the back. Half dead, crippled by years of mantle abuse, she’s confined to her bed, unable to breathe without a respirator and constantly overseen by doctors. Her nervous system is so degraded she’s half-paralyzed, and finds it hard to speak without the doll transceiver. Still though, looking at this wretched creature, Siren compassion in her heart. She steps up to Trixie’s side, kneels beside the bed, and forgives Trixie for abandoning her in the orphanage so long ago.

To which Trixie responds, with a contemptuous sneer and a roll of her eyes, that she’s not Siren’s mother. Really she thought it was obvious. The collectors call her “Cousin Pinkpony.” And what is a cousin but the daughter of my mother’s sister? The hair sample came from Twilight. Siren is Twilight’s daughter, Sine is her father, and the “old friend” Trixie was repaying a debt to by saving Siren was Twilight before she was corrupted by mantles. Trixie was trying to do what “the real Twilight,” would have wanted. Fair repayment for saving Trixie from the Alicorn Amulet.

Left in shock, Siren is assaulted by visions from Rarity’s tea, where she finally beholds what happened. Sine was indeed real, a stallion who moved to Ponyville before the Blight, and who was rather sweet on Twilight. Despite his odd ideas about selfishness and generosity, Princess Celestia liked him at first. Everyone liked him, really. No matter what he said, he has this charismatic, almost hypnotic air about him. You felt you could trust him. That he could look into your eyes and just understand you.

Like Siren always seems to have a bizarre understanding of ponies. How she always knows what they’re thinking. How she can tell one silence from another.

But soon, even as Twilight and Sine became a romantic item, Celestia grew suspicious. The Blight had begun, and while there was nothing connecting Sine to it, ruin always seemed to follow in his wake. He visited a town, and a week later, riots broke out. He sold produce to a city, Blight spread throughout its crops. Celestia could prove nothing, but the amount of circumstantial evidence piled higher and higher. Sine had a Suspiciously Unconfirmable Backstory, with nopony who could say they knew him before he arrived in Ponyville. And there he always was, stirring up sentiment against the Princess.

Finally, Celestia had him arrested. In the confrontation that would become legend, Sine burned his farm before letting Celestia touch it. Though she had no intention of seizing his crops, she found it impossible to convince his furious disciples otherwise. She dragged him to Canterlot Palace, and Twilight with him, demanding Twilight and her friends use the Elements of Harmony upon him. He he really was what he seemed to be, he had nothing to fear, but Celestia highly doubted that was the case. Whatever he was, he wasn’t a pony, she knew.

Twilight and her friends hesitated however, and in the face of their hesitance, Sine gave an eloquent speech about the importance of individual freedom, and that the Elements of Harmony were not a weapon to be used against Celestia’s political enemies. He offered to go to jail -- for burning down his farm, since he was admittedly guilty of arson -- but dismissed her other concerns as simple paranoia. He wanted what was best, and besides, he couldn’t really mean Celestia any harm. She was Twilight’s mentor, and harming her would make Twilight sad. He could never hurt his true love that way.

Celestia looked at Twilight, and looked at Sine, and understood that Twilight would not raise a hoof against him. And so she called all her power into her horn, and launched a brilliant, burning ray directly at his heart, to burn him to ashes.

It bounced off. Then in a blur of motion and shadow, Sine hit her hard enough the stone beneath her cracked. It was a brawl between creatures that were not quite mortal. Celestia had wings, a horn, countless spells and her mighty strength, while Sine seemed to be an unstoppable juggernaut, with skin like iron and blows that shattered stone. Back and forth they went, until Sine broke one of Celestia’s wings with a thrown chunk of marble, and she fell to the ground. He pounced atop her, lifting a hoof to smash her skull into paste.

Then, Twilight blasted him with her horn -- through the ears, instead of across the skin. He staggered, still alive with an otherworldly vigor despite half the contents of his skull being reduced to ash. But Celestia took advantage, and in his stunned state, she slew him.

With Sine dead, the Blight began to fade almost immediately, and the riots calmed. They never found out who or what he really was. Twilight found out she was pregnant two weeks later. When Siren was born, she had fangs. Surgery removed them, but everypony knew.

Perhaps it was the lingering effects of Sine’s dark magic on her mind, or perhaps her grief was genuine, but she never forgave Celestia for the fact that her child would grow up without a father, and she denied all claims that Sine was responsible for what befell Equestria. After Siren’s birth, she locked herself in her library, and descended into a negative spiral of grief, rage, and denial. Concerned for her student’s mental health, Celestia forcefully intervened, and when she found that Siren was not being fed or properly cared for, took her to Canterlot.

To Twilight’s warped mind, Celestia had just stolen her daughter from her, and that was all it took to push her over the edge. Her grief turned to a focused madness, a narrative of Celestia’s wickedness, and in time, she left Equestria.

Her visions over, Siren awakes to find Neptune’s Bounty is under attack. Trixie’s empire is crumbling, and with it gone, the last vestige of resistance to the regime will crumble. She and her friends, Berry, Echo, and Green, go out to make their last stand, facing down the Elements of Harmony, including Twilight.

Knowing there’s no way out of this, Siren tries for a hail mary play, giving a speach where she insists that her friends are the true Elements of Harmony. Trixie is Magic because she brought everyone together, and Berry is Loyalty because her her caring for Trixie. And Echo is, uh… honesty? Maybe. That’s about as far as she gets before ponies start giggling. They aren’t the Elements of Harmony, Twilight points out. In fact, they’re all awful, awful people.

With death now inevitable, Siren gives one last speech, defending her and her friends to Twilight. Because Twilight is right, they are deeply flawed people, but that doesn’t mean they’re irredeemable. Echo is a drunken facist womanizer, but he has lines he won’t cross and things he stands for, and his choice to defend Siren was genuine. Green is a murderer driven by jealous rage, but she’s also a compassionate and caring friend. Trixie is a schemer and a thug, but she always held Twilight’s kindness in her heart, and paid it forward to Berry when she was suffering from crippling depression. And Berry, for all she pretends to be an emotionless robot, truly loves Trixie as a friend, and was always there for Siren even when Siren didn’t deserve it.

None of them, Siren admits, are heroes. But they’re not pure evil either. Even if they don’t always show it, they have good in them, and it’s those little moments of compassion that are the reason Siren is still alive and standing there. Because goodness isn’t a force that can be wielded as a weapon, and friendship isn’t six magic stones. It’s a power that is present in all ponies, however faintly, that makes their lives better and gets them through the day. And no matter how much Twilight and her friends posion these ponies souls with mantles, they can never extinguish that light completely.

Then, Siren realizes she’s glowing. Purple -- like the Element of Magic. But she’s not the only one. Trixie is glowing that shade too, so is Thunderlane, officers and rebel leaders. Echo is red like the Element of Loyalty, but so is Berry, so are the rebels who stuck by eachother. Green is Kindness, but so is Zephyr and all the ponies who did so many little things along the way. Golden Palm is Generosity. And so on and so forth. All the ponies in the city, glowing, just a little, and Twilight and the other corrupted Elements can’t stop it.

Twilight and the others shriek as Elements of Harmony come to life against their will, wrapping them up in a brilliant rainbow that soon spreads outwards, consuming the city. Markers panic and flee in all directions as the city starts to crumble, tumbling down around their ears. Siren is left alone to ponder as all her friends scatter, realizing that Sine was afraid of the touch of the Elements of Harmony. She is his daughter, with the same powers and the same evil that dwells in her heart, and she remembers the stories of King Sombra getting blown into pieces by that same power. She wonders if the touch is going to kill her, and after a little while, decides that would be okay. She sits there and shuts her eyes, waiting for the end to come.

The rainbow expands outwards, enveloping Siren and the others. The city rises and shakes. And when Siren next opens her eyes, they’re on the surface. Vision has been transformed, from an underwater city into an artificial island above the sea floor. The force fields are gone, and the windows are open to the air, and let the sunlight stream in. The extra cutie marks are gone. The bottles of mantles have transformed into bottles of seawater. And the fields of Poison Joke have blown away like dust in the wind.

Green is a real unicorn mare, and will never need magic to look that way again. Her impossibly perfect looks are gone -- in fact, she looks like a farm mare who just happens to have a horn -- but she doesn’t care. That’s all she ever really wanted.

Berry’s depression is cured, along with her crushing addiction. For the first and only time in the story, we see her display emotion as she cries with joy and sweeps Siren up in a hug.

Trixie is no longer crippled or addicted. Golden Palm’s wings are fixed. Applejack’s children are cured. Ponies all across the city find the no longer need magic to transform themselves. They are exactly what they always wanted to be. And that’s enough.

Siren has a moment with her own cynical thoughts, sneering at what a saccharine-sweet ending this is, when she hears a shriek and turns to see Echo and Rarity struggling. Rarity’s extra cutie marks are gone as well, along with her malevolent air. While the other Elements of Harmony watch in horror, he’s holding her to the ground, trying to stop her from killing herself as she screams that she doesn’t want to live with the memory of what she’s done. The horrible things. It was all her fault.

Some part of Siren enjoys seeing that -- knowing that the perfect ending isn’t quite so perfect. Then she chastises herself for the thought, realizing that the Elements of Harmony did not, in fact, cure her of Sine’s evil. She doesn’t get that easy an out. After a moment of consideration, she wanders over to the Elements of Harmony, which has been transformed into a civic monument depicting the new layout of the city beneath the sun. Sitting beneath them, she finds some paper in her belt-pockets, and begins composing the Letter to Celestia we saw all the way back in the opening chapter.

Dear Princess Celestia,

It has been some time since I wrote you. I imagine you did not expect to ever hear from me again.

Much has changed since the last time we spoke. I have changed. I wonder—will you recognize me, next we meet? Will you recoil? Perhaps, yourself eternal, you are used to others changing around you.

You lied to me, Celestia. You called me your faithful student. You told me you would always be there for me. I’m not sure I can forgive you for that, but I understand why you did it. I know what you were trying to protect me from.

I’m rambling now. I suppose I owe you some explanation of where I have been all this time.

When I was a foal and asked you why you took me as a student, you told me that I was going to change the world, that I was destined to do great things.

You were right.