Just An Average Trip to Equestria

"Penny dropped yet?" asked Twilight, beginning to laugh as Sunset tried to work out how to use her wings.
"Yeeeeaaaaaah," Sunset said slowly. "Wait. Summarise everything going through your head right now."
"Oh. My. Gosh. We. Have. A. New. Princess."
"Yeah I know - hang on! Just because I'm an alicorn, does it mean I have to be a princess?"
"Yes. Get used to it."
"You what?!"
Celestia took over. "Twilight's right - all alicorns are royalty. This is a lot of alicorns at once - Shining Armour became an alicorn last month."

This was news to Sunset. She gave Twilight an accusatory look. "You were supposed to tell me everything important that happens in Equestria and you couldn't be bothered to tell me that your brother is an alicorn too now."
"Yes," Twilight apologised, "when I used all my magic to stop the battle between the Crystal Empire and the Dragon Lands, I may have been helped by my older brother. Nopony even noticed - he was wondering how long it would take anypony to spot them - until Princess Cadance brought it up. She said to him, "Look at your beautiful wings!" And that was that. He was already a prince, but we celebrated anyway because there hasn't been a male alicorn since King Cosmos. And he died - what, two thousand years ago?"
"Two thousand, seven hundred and forty nine," Luna corrected. "I remember him like he died yesterday. Good old Dad."
"Soooo," said Sunset,"do I have to have a coronation and a party and all that nonsense?"
"Yes," answered Twilight.
"Oh hell."

The news managed to spread like wildfire. By the end of the day, everypony in Equestria knew about the future Princess Sunset Shimmer, Ambassador For The Human World.
Including the voices inside Celestia and Luna's heads. There were no nightmares, so Luna walked into Celestia's dreams. They found their inner demons - Nightmare Moon, the evil version of Luna, and Daybreaker, the evil Celestia that Starlight Glimmer imagined - in deep conversation. Their chatter died away as the Princesses approached them.
"Oh," Daybreaker said with obvious displeasure, "my weaker self, and your weaker self, sister."
"Could not have phrased that better myself," replied Nightmare Moon.
"I thought I told you two that you don't exist," Celestia interrupted.
"Ah, well, Celestia. This is your dream. This is your party. You invited me by dreaming about me. The same goes for our sister Nightmare Moon."
"Our? Luna is my sister, but Nightmare Moon is a thing. So are you. By the way, you always get gatecrashers such as yourselves at popular parties. By the way, I'm curious. When did you make up for trying to kill each other?"
"When you and Luna made up."
"So you two are just more extreme versions of us."
"I like that."
"Then I should not have phrased it that way. What are you talking about?"
"Later. Remember, this is a dream. Anything is possible. Including being myself." Daybreaker and Nightmare Moon disappeared.
"Hey Luna," called Celestia, but she was gone.

She was in Sunset's dream, which had turned into a nightmare. Sunset was at her coronation as the new Princess of Equestria, but she was making a fool of herself without meaning to and the crowd were laughing at her. A dream version of Celestia looked down at Sunset and said, "You are useless. Twilight Sparkle and Starlight Glimmer are so much better than you. You are an embarrassment. Have you learned nothing hiding from me in that other world?" Sunset tried to speak, but spat out teeth instead.
"Hey Sunset," whispered Luna. Sunset turned to her. "Do you really think Celestia would do that to you? She's not real. This is a dream."

The scene dissolved and the two alicorns found themselves on a cloud. Sunset was human, and was looking into a huge mirror. Her reflection was that of a huge winged troll.
"Go away demon," Sunset told it.
"No, I am part of you," it replied. "There is nothing you can do to get rid of me forever. I will always come back."
Sunset turned into an alicorn. "You can't follow me into Equestria."
The reflection changed. An ugly alicorn covered in orange scales stared back at her with beady black eyes. "Oh yes I can. I have big plans for both Equestria and the human place called Earth. Midnight Sparkle might even agree with me."
"Ahem, Miss Demon Reflection," Luna said. The demon looked at her. "Now, demon, just because you can't be destroyed, it doesn't mean you cannot be locked away for a while." Luna made a box out of magic, took the demon out of the mirror, and shut the demon in the box. It tried to escape, but Luna made a padlock and locked the box.
Sunset looked up at Luna. "Thanks," she said, "She kept bugging me. I'm nervous about being a princess. I feel like everypony expects me to be some heroic mare taller than Celestia, who wears armour made of rubies and could kick Tirek's head off if I wanted to. I'm not that kind of pony."

Luna sat opposite Sunset. "Am I that kind of Pony? No. Is the job easy? No. Am I still a princess? Yes. Your demon is your worst enemy. You get dragged down. Maybe these wings will help you fly away from it."
Sunset smiled. "Could you teach me? Twilight could, but sometimes you just need a break from your friends to stop being irritable."
Luna's horn lit up and a huge blanket of clouds appeared below them. Sunset looked curious. "So if I fall, I fall onto that and bounce back up?"
"Yes. Now, step back about ten paces, then take in a big breath and run forwards. Open your wings before you get to the end of the cloud. Then, when you jump off, flap them as hard as you can. This is a dream, so you're not actually flying, but that's how you do it in real life." Sunset stepped back, then ran forwards and unfolded her wings. She jumped off the cloud and fell and flapped her wings again and again and -

Flew.
"Sunset to Luna, I am airborne!" she yelled gleefully. "Coming in to land in three, two one-"
Her hooves hit the cloud, but she kept moving and did a roly-poly before landing on her bottom. She laughed. It was one of the best moments of her life.