"Why hello, my dear stud-"
"Don't even try to say it!"
Sunset barked with all the air she had in her lungs. Her feelings were conflicted: a deadly mixture of fear, hate, rage and sadness overcame her as her pursuer didn't even try to deny her identity. To be honest, Sunset didn't think it was her former mentor until she called with her fake name: the mare who followed her seemed just a normal mare you'd find everywhere in a city like Manehattan. Sunset nervously watched to her left and her right, trying to find guards ready to jump on hair, but she found none.
"Where are your guards?"
"I didn't bring them, my little sun-"
"STOP IT!"
Only when she shouted she noticed that no-one on the streets were paying attention to the two mares in the alley. Then she realized:
"You. You set up a damn bubble of silence! Are you going to mock me for not being able to pop them up back in the day? I'm not going anywhere with you, I'm not even going to be sent to Tartarus! I'd rather die than be your prisoner for eternity!"
Sunset wasn't ready to face her former mentor, not even while in disguise. She knew she had to face her, but she couldn't imagine it being so soon and so out of her control If she had to have atalk with Princess Celestia, it had to be at her conditions.
"Please, Sunset, just liste-"
"Like Tartarus I'll listen to you! Are you here to say what? That I was a bad pony? That I was a stupid little filly with maniacal dreams of alicornhood? That I shouldn't be here in Equestria? It was your own damn fault when you showed me that bucking mirror! I wouldn't had to endure what I endured in the human world! I turned into a literal demon because you denied me the knowledge you flaunted in front of my eyes! You made my life a living Tartarus! And you want me to listen to you!?"
Tears were flowing out of Sunset's eyes, as all the bad memories hit her brain with the strength of a full-throttle train: the mirror, the arguing with Celestia, the escape to the human world and her reign of terror, the steal of the Element, being turned into a demon and lastly, Anon-a-Miss and the fake friendship it broke. Only then Sunset saw another two eyes crying: Celestia was sobbing. No words were said for a while, both the mares were letting their eyes talk. The Princess was the first to try again, this time decloaking herself and letting her natural body show to Sunset inside the bubble.
"No one will see me like this here, my little pony. And I'm... sorry. For everything."
Sunset was astonished by that affirmation.
"What? What do you mean?"
Celestia still saw fear in Sunset's eyes, and could sense that the young mare was scared about this confrontation. They both weren't ready for that, but Celestia made the error to follow Sunset too closely, while Sunset made the error of not being completely aware of her surroundings.
"I mean what I say, Sunset. I made an awful error showing you the mirror that time, but after so much time being basically alone, without having a single pony being able to spend time with you, wouldn't you rush things to ensure her survival? I'm immortal, Sunset, I'm basically the Sun's incarnation. I loved many ponies in the past and had to bury them all, and I couldn't bear to lose you too. I was selfish and tried to manipulate you by giving you the desire to become an alicorn. I couldn't predict that your reaction would be so explosive. I just wanted to give you a little push, and I ended up ruining everything. And I lost you like I lost everyone else."
"But you didn't know that the mirror connects to another reality. And you didn't know about my delusions of grandeur either."
"I'm the one at fault here, Sunset, and we both know it. I failed as a teacher, I failed as a friend, I failed as your moth-"
"NO!"
Celestia was taken aback by that reaction. She saw fury and no more fear in Sunset's eyes, a blazing and deep fury she came to know well in the years she spent being Sunset's mentor.
"You took me up when I was an orphan, you gave me everything. I don't even care if you took me up because I was good at magic or to fulfill whatever plan did you have, the fact is that you took me up when I was alone and gave me food, shelter and knowledge. You didn't fail, I just wasn't enough to satify your standards. So please, don't even think about saying you failed at something."
Sunset tried to continue to speak but Celestia tackled her full force into a bone-crushing hug. The two mares stayed locked in that position for quite some time, until Sunset asked:
"But... how did you find me?"
"Well... I might or might not have detected a certain magical signature when someone decided to cross the mirror again."
"Wait, you traced me?"
"I just sensed it, but I wasn't the one who traced you. I left that to a more expert pony than myself regarding ponies as single elements instead of a big crowd."
"Er... I don't think I understand... There's someone more able than you in tracking magic?"
A third mare entered the bubble of silence with apparently no effort at all. Her disguise started slowly to disappear revealing a dark blue pony with a mane resembling the night sky.
"Hello Sunset. I am-"
"IT'S THE MARE IN THE MOON, TAKE COVER!"
Sunset bolted out of Celestia's hug and through the air until she slammed into the wall provided by the bubble of silence: being casted by Celestia, it would've taken similar power to hers to get out of it.
"While I indeed was the 'Mare in the Moon', Sunset Shimmer, now I'm no more than Princess Luna. And I am really pleased to make your acquaintance."
Sunset seemed to think for a couple of seconds until she realized:
"Wait, the Mare in the Moon is actually Princess Luna, which is Princess Celestia's sister, which basically means that Celestia sealed her own sister in the moon? And here I thought my relationship with Princess Celestia was complicated."
"She had a good reason for sealing me up, Sunset Shimmer. The Nightmare possessed me, changed me into an avatar of evil, and my dear sister did what she had to do to ensure Equestria's safety, at cost of caging her own sister. I don't blame her for that, nor you should. My sister was always the perfect ruler, and every action she took was for the best. I can only speculate, but she probably thought that showing you the mirror was the best course of action."
Celestia nodded, and said:
"Well, enough of the past though. Sunset, why did you decide to return?"
"It's kind of a complicated matter, which would involve a lot of explaining, self-loathing and mild anger. Though if you really wish to hear it, Princess, may I suggest moving from this alley? I don't mean to be rude, but a bubble of silence isn't really the best of places."
Luna beamed up and replied:
"Well, I do know a place where we can go, though both me and my dear sister would need to get in disguise."
Luna and Celestia donned their disguise personas and after Celestia removed the bubble of silence, Luna started to lead the way:
"It's not far from here, follow me."