Scenario DB-LS34:
Sunset slowly stepped through the mirror. She wore an orange gi and her hair looked a bit more spiky than before. Her firm gaze was focused solely on Celestia.
“Celestia!” Sunset spoke up. “I’ve trained for the last thirty moons with the strongest warriors of that other dimension to become one of them. It was a long and hard time, but it paid off as I’m now finally strong enough to face you and prove that I’m worthy. I will not hold back and expect the same from you! So get ready to fight!
“AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA!” With that Sunset got into fighting position. Her spiky hair turned golden and stood straight, while a golden aura formed around her.
Celestia looked conflicted about fighting her former student at first, but that turned into strong resolve. “If that is what you want, Sunset Shimmer, I will fight you!” And Celestia, too, got into fighting position, her horn glowing.
“Alright, I’m going to show you my strongest attack!” Sunset put her hooves together and then held them on her side to charge energy between them.
“KAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA…”
“I’m ready, Sunset”
“AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA…”
“Hit me with your best shot!”
“AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA…”
“Any time now.”
“MEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE…”
“How long will this take? I have some more plans for today.”
“EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE…”
2 episodes later…
“HAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA!”
Sunset struck out her forehooves to shoot a giant shockwave at the throne, obliterating it and every wall behind it. After the attack faded Sunset returned to her normal form. She stood there panting and watching the remains of the throne room.
“I… I did it… I did it! Yes! I beat Celestia! I’m better than her! Take that, perfect pony princess! Hahahahaha!”
While Sunset still celebrated her ‘victory’ Celestia walked into the throne room from the other side. A bit of toilet paper still stuck to one of her hooves. “Did I miss something?”
Sunset was more than disappointed. “W-W-What? That’s unfair! You are not allowed to move while I’m charging my energy. Now I have to do it all over again.”
Sunset’s hair turned golden again and the aura returned.
“AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA…”
Celestia sighed. “Then I’ll wait until blocking your attack…”
“How could anyone stand through such long-winded battles?”
Scenario KD-TE24:
Three ponies walked through the magical mirror. Celestia immediately recognized her former student, Sunset Shimmer, the other two seemed unknown to her. One was a small filly with white fur and a white-lavender mane. The other was a mare in a maid-costume with green fur and a blonde mane. The odd part was that both had dragon-like horns and tails. Celestia also felt like one of them looked familiar.
“Oh! That’s where you lived, Sunset?” came from the filly.
“Yes, Kanna, this is Canterlot Castle, the place I grew up in. And the big, white, crowned alicorn over there is my former teacher, Princess Celestia.” Sunset pointed at the princess. She then hastily added. “Who’ll hopefully forgive me everything I said and did, when I give her a really honest apology and say ‘I’m really, really sorry’?” Sunset gave a shaky smile.
Celestia answered with a sincere smile.
Sunset looked like a huge weight fell off her shoulders. “In that case I should introduce you. Princess, these are my friends Kanna and Tohru.”
At hearing the name Celestia narrowed her eyes. She already wondered why the latter had growled like a territorial dog for the last minute. “We meet again, Tohru!”
“So you do remember me after all, Celestia!” Tohru replied.
Sunset looked puzzled. “Eh, a bit of context, please?”
“I heard that a long time ago Lady Tohru and Princess Celestia met while travelling through the worlds,” Kanna answered. “Though it didn’t end very well.”
"But Celestia is a very forgiving pony." Sunset wondered. "Why would she hold such a grudge for so long?"
“YOU ATE MY FAVOURITE CAKE, YOU FILTHY DRAGON!”
“Now I understand…”
“You are still hung up on that? I obviously did your figure a favor, stuck-up princess!”
Celestia flared her wings and her horn started gathering magic. Claws came out of Tohru’s hooves, while her teeth sharpened and a fireball grew between them. Both were prepared to start a battle to the–
“Wait, wait, wait!” Sunset interjected. “Tohru, Celestia, you two can’t just randomly start a fight where you destroy everything (and probably everypony) in the whole castle… town… continent. Either you two make up or fight at a safe location!”
Claws and fireball gone, Tohru pointed at the closest wall where only a second later a portal appeared. “Alright, I know a safe place where we can take our battle.”
“You’re right. Let’s go.” Celestia silently walked over to the portal. Asking for my forgiveness, worrying for others and a monster like Tohru listening to her… Sunset must have come a long way.
Celestia stepped onto the huge, grassy field behind the portal. “You can come now!” she shouted to the others who still were on the other side of the portal.
Then Tohru closed the portal.
“That was a dirty trick…” came Sunset’s response, unable to decide whether she should be angry or proud of the dragon maid.
“I protected the order of this world just like you wanted. It was a peaceful resolution.” Tohru answered.
Sunset sighed. “Let’s just look around this place until Celestia returns and that whole situation inadvertently repeats itself. Come on, I’ll show you my old room. Pretty sure Celestia left everything as it was.”
“Yeah!” the dragons replied in unison.
Meanwhile on the aforementioned grass field...
“One day I’ll get you, TOHRU!” Celestia shouted into the sky.
“Celestia can be pretty unforgiving when it’s about cake, huh…” Luna figured.
Scenario YY-AA36:
Celestia sighed. Sunset has been gone for so long, now. I don’t even want to imagine what kind of terrible monsters were waiting for her on the other side… “I hope you’re alright wherever you are, Sunset.” she finally spoke out loud.
“I’m right here beside, Celestia.” came suddenly from her side. Celestia turned and, to her surprise, saw Sunset standing right there.
“Sunset, you’re back! And I’m so glad to see that you’re alive and well.” Celestia embraced her student. “But where were you and since when are you back?”
“The world was nothing special. It was filled with these weird, hairless monkeys, called ‘humans’, and they all went to school normally.” Sunset explained. “There were some nice girls, one more hyperactive than the other, I spent some time with in their school club. Oh, and I’ve been back for like an hour.”
Celestia thought back to what happened in that last hour (not much). “In that case I have to apologize. I somehow just didn’t notice you. It was like you were invisible.” –Sunset’s eyes widened– “Is something wrong?”
“I just had to think of a certain girl from the school. She also had the problem that people never noticed her or completely forgot she was there. That was pretty similar to what happened just now, but that would be pretty weird and–”
Akarin~
And Sunset disappeared.
“Sunset! Where are you?” Celestia looked around frantically.
“OH MY GOD! IT’S CONTAGIOUS!” Celestia heard Sunset’s disembodied voice screaming. “I knew spending time with Akari was a bad idea. I’m a main character! I’m important! Unlike her I can’t be ignored!”
“Akari doesn’t like what you say. Why did you even invite me to come with you?” another invisible and still unnoticed girl complained with an unseen pout.
“I know exactly how being ignored feels–”
Lunarin~
And Luna disappeared, too.
“Not. Funny.” came Luna’s disembodied voice.
JJ-DM1:
On a calm afternoon Celestia sat in her throne basically doing nothing. Suddenly blonde-haired stallion jumped out of the mirror and ran up to her. Before the princess could process what was happening, he reached her and kissed her right on her muzzle. Celestia’s eyes widened, too shocked to respond in any other way. The stallion finally broke the kiss and took a few steps back.
“You were expecting your student, but it was me, Dio!” he exclaimed before jumping back through the portal again.
A few moments later Sunset Shimmer appeared through the portal. “Did he kiss you?” Celestia nodded. “DIIIIIIIIOOOOOOOO!!” Sunset shouted enraged before jumping back through the portal, too.
Celestia’s brain finally caught up and gave the only appropriate response it could think of, “That was… bizarre…”
“I certainly didn’t expect that.”