An inspection of the aforementioned dungeon turned up exactly what Sunset had promised: The petrified, immobile forms of Princess Celestia and Princess Luna. Their looks of horror remained transfixed for all to see.
It took a great deal of effort (and several royal guards) to haul the huge block of stone out of its hiding place and out to the royal gardens overlooking the palace. The setting's symbolic nature did not go unnoticed by the six mares as they prepared to activate the Elements of Harmony to free the royal sisters.
It was a risk to be sure, but if the Elements of Harmony could undo Discord's stone imprisonment after twice imposing it upon them Twilight was hopeful that the same could hold true for the mighty alicorns. She made sure to keep a close eye on the defeated Sunset Shimmer too, not wanting to let the now de-demonized mare out of her sight.
The elements began to glow one by one, forming a trail of rainbow energy that flowed to the tip of Twilight's crown and then shot out at the statue! There was another blinding flash, and the statue began to crack bit by bit! When the light faded, there stood the royal sisters in all their glory. They even still had their crowns and royal horseshoes.
Celestia was the first of the two to speak up. "Sunset Shimmer? Have you finally come to your senses and..." She began in a stern tone of voice, but it was cut off when she saw six very recognizable faces standing before, including a face she thought she'd never see again! "Twilight!" She exclaimed as she shed her usual stoic composure, rushing over and hugging the young alicorn tightly. She didn't even care that tears were streaming down her cheeks! "Oh Twilight! This has to be a dream! I thought you were..."
Twilight shook her head as she returned the hug and shed tears of her own. "I survived, barely. I'm SO happy to see you again!"
But Princess Luna coughed into a hoof as she glared. "Not that I mean to interrupt this touching moment, but what is the meaning behind our release?" Her glare turned to the one who had imprisoned her and her sister. "And why is Sunset Shimmer now just a plain old unicorn? Whatever happened to her original appearance?"
Sunset gulped and shrank under the stern gaze, even while she was trying hard not to laugh. She only knew of Luna's voice through Vice Principal Luna, and she knew that Vice Principal Luna could never be this scary if she tried. "This is my original appearance, Princess Luna. I assume you are a princess in this world."
"Indeed I am, no doubt my sister told you about me when you were her student," Luna declared as she kept up her harsh glare. "But why is it that you lied to us about Twilight? And why have you now allowed for my sister and I to be set free?"
"Sunset Shimmer thought she'd killed me, but she was wrong. My friends and I were able to defeat her and take away most of her powers," Twilight explained to the royal sisters. "Everything can be explained in due time, but you need to hurry up and take back your abilities to control the sun and the moon. Sunset's unicorn body won't be able to contain such powerful magic, it'll destroy her from within!"
At that Luna flashed an unusual smile. "A chance to take back power that was never meant to be wielded by a power hungry ex-student of my sister's? How could I refuse?"
Celestia was quick to add as she ended her hug with Twilight. "Sunset Shimmer, know that although my sister and I are taking this action to save you, you are not off the hook. You must still face punishment for the crimes you've committed."
"Please, just hurry!" Sunset pleaded as she bowed before the princesses! "The sun will need to be up soon! I'll face whatever punishment you think is best, I promise."
So it was that Celestia and Luna placed their horns to Sunset's forehead. Everyone else stepped back as the horns glowed and surged ominously with dazzling yellow energy for Celestia, and cool blue energy for Luna. At last the glowing stopped, and an exhausted Sunset Shimmer collapsed as her mane and tail fell into a frazzled, disheveled state of appearance. Just like that it was all over. She was now back to where she had been on that fateful day long ago when she had fled through that magic mirror.
After lowering the moon and raising the sun as they had done so many times before, the royal sisters immediately turned their attention to the unicorn they had just saved. Celestia was quick to give the order. "Guards, take Sunset Shimmer into custody and bring her to the throne room. There are some things that must be addressed."
Luna added. "And Twilight Sparkle, if you and your friends would be so kind as to join us in the throne room, that would be most appreciated. I think everypony would like to know just where you and Spike ended up, and what lies beyond that mirror."
So the recently reunited group of friends followed the captive Sunset Shimmer and the royal guards escorting her as they all adjourned to the throne room within the castle. Celestia and Luna took their respective seats at their thrones, staring down and casting daggers at Sunset as she remained within the custody of the royal guards.
Twilight took the liberty of explaining her journey to everyone in the throne room a moment later. "What I tell you is true, as hard it may be to believe. Beyond that mirror lies a world so similar to ours in many ways, yet so different in many others. In that world there exist creatures known as humans, and most of them attend a high school named after this city. It was this high school that Sunset Shimmer ruled over with an iron first."
"No wonder she was able to amass such a powerful army so quickly." Princess Luna remarked even as her tone of voice did not change.
"All this time, I never knew. I thought my former student had been lost to me," Princess Celestia commented and turned to look at Sunset Shimmer. The majestic alicorn had tears in her eyes again, but it was clear to all that these were not tears of happiness. These were tears of frustration and anguish. "Why, Sunset? Why didn't you ever come back until now? Why did you run away and turn to the dark side? You were my most promising pupil, you were destined for so much more."
At that Sunset stomped a hoof down and snorted. "Was I really?! That mirror showed me what I could be, but you were always holding me back! I saw then and there that I could've been a princess just like you! I could've been worshipped, admired, respected and most of all adored! Admit it, you were afraid of me. You feared that I would become a more powerful alicorn princess than you and would eclipse you as you did your sister."
The sun princess only shook her head in dismay. "I showed you that image in the mirror in the hopes that you would come to understand how important friendship was. You repeatedly doubted yourself even when I told you that you could be far more than the struggling unicorn that you were when I first met you. I tried not to get too attached, but you became like a daughter to me. Losing you after you went behind my back stung just as much as when I had to banish my sister to the moon."
"Lies! How long did you wait before you replaced me?!" Sunset demanded as her eyes narrowed. "A week?! A month?! It seems like you got everything you wanted when you took Twilight under your wing. You didn't have to say a word, I got the message the first time I came back to Equestria. You no longer wanted me, you'd regarded me as a failure. Then and there I made up my mind. I was going to prove you wrong! I was going to make you realize how powerful I could truly be! I would make you bow down before me and acknowledge me as better than you," She then let out a sigh. "It wasn't supposed to be this way. I didn't want to replace you like you did me. I only wanted you to realize your mistake."
Princess Celestia sighed anew as she struggled to wipe away the tears. "It's really too bad you became a power hungry monster, Sunset. Before all of this I held out hope that you would find your way. That Twilight would be able to get through to you in a way that I never could and make you understand the importance of friendship," And she turned her head away from the unicorn. "But after all you've done I can no longer be justified in showing you leniency. Your crimes are too great and too numerous to truly count."
"Then go ahead, do your worst!" Sunset roared in defiance as she managed to break free of the royal guards' hold on her! "Do to me what I did to you! I can't simply run away and hide in the other world again, I'll be wanted for crimes in that world too and you'll just send Twilight to hunt me down. I know what fate awaits those who betray Equestria. Banish me to the moon or the sun if you so care. Imprison me within either for a thousand years, or perhaps even longer. Just get it over with!"
Celestia was silent for several minutes as she continued to have her head turned away from Sunset. No one else dared to say even a word.
No one that is, except Twilight. She boldly stepped forward and cleared her throat. "Princess Celestia, you must understand that Sunset Shimmer allowed us to defeat her. I can tell that her heart was not into our last fight, she wanted to lose."
Sunset growled and hissed. "How do you know that?! How could you possibly know I wasn't just exhausted or otherwise unprepared?"
"Because if you had truly wanted to continue your rule indefinitely you most certainly wouldn't have been looking up spells on how to undo a petrification spell," Twilight explained to the unicorn. "And you would've tried to burn me completely like you did in the human world. Your mere actions gave you away without you needing to say a word," Then she continued with her plea. "I know Sunset did a lot of terrible things, Princess Celestia. I know that you feel hurt by the way you parted terms and betrayed by the way she returned. But banishment is not the answer, it won't heal the wounds she's inflicted."
"Then what would you have us do, Twilight Sparkle?" Luna questioned as her eyebrows arched upward ever so slightly. "The fact remains that she is a traitor in this world, and apparently quite the monster in that other world as well."
Surprisingly, before Twilight had a chance to make any sort of proposal, Sunset Shimmer herself trotted forward and bowed her head. "At least let me return to Canterlot High so that I can make amends with everybody I hurt in my pursuit of power. I imagine it'll be a long time before anyone there is even remotely willing to trust me again, especially a certain someone whose love for me I took for granted. And maybe someday... I'll come back to Equestria, truly ready to leave behind my power hungry ways of old and start anew."
"Well, sister, what do you say to such a suggestion?" Luna turned to her sister. "After all, we don't know for sure how the justice system in the human world works. It might not hurt to let them deal with Sunset Shimmer for a while, as a way to ensure they won't try to come after us to get to Sunset."
Yet Celestia remained silent. She said nothing for the longest period of time.
Bowing her head, Sunset trotted back to the guards. "Just throw me in the dungeon with everypony I've imprisoned while you decide my fate. That shouldn't be too much for you."
Only once the unicorn began to leave (preparing to see herself out with the royal guards continuing to watch and surround her) did the silence in the room break.
Celestia turned back to her former student and now wept openly. "I can't bring myself to forgive you, Sunset Shimmer, even though I want to more than anything. For your own safety I shall accept your proposal. Your return to the human world shall be framed as a self-imposed exile. I will leave it up to the ones in charge in your world to decide how long it should last. Maybe someday it'll be possible for us to reconcile."
"I.... hope that someday comes, for both our sakes," Sunset wept in reply. "I'm sorry I ever thought to oppose you. All it did was burn us both, along with so many others who didn't deserve to be dragged into all of this."
"Well then, shall we be on our way?" Twilight asked the unicorn. "I'm not sure how long the portal will stay open, and we don't want to miss our window," To Princess Celestia she added. "Don't worry, I'll make sure this whole thing is left in good hands."
Twilight expected the princess to ask what a hand was, but she didn't. It was clear to her and to everyone that the wounds from Sunset's return and betrayal cut deep.
And all Sunset Shimmer could do, was lament to herself at how she cost herself the chance to have the closest she could remember to a mother. Now she was stuck without a friend in the world in either Equestria or the human world.