"Woo hoo!" Rainbow Dash looped in a delighted spiral through the air above the throne. Spitfire danced with her, the two of them swooping and circling around each other. Rainbows and flames trailed behind them, drawing a double helix of light as they circled upwards together. Twilight laughed in delight to see it. Her friend, restored as she had hoped, was a wonderful sight. The other Elements looked better as well, tangled dreadlocks restored to smooth manes, gaunt sides returned to plumpness, cracked hooves smoothed and polished.
"It's so pretty!" said Fluttershy.
"It's a sight for sore eyes," said Pinkie Pie, staring up at Rainbow and Spitfire.
"Oh." Fluttershy ducked her head and smiled. "Yes! But I mean the necklaces. Look, yours has your cutie mark on it."
"Ooh! Wowie Zowie! It does!" Pinkie grinned and bounced in place. The five of them wore their elements, and Twlight felt the gentle weight of Magic's crown on her head. Everything looked just as it had one year ago, on that other world.
Or almost everything. Twilight could see no sign of any second Luna. It seemed that Nightmare Moon has spoken true when she'd said she'd killed her former self. The Luna she knew, her mane flowing and full of stars, smiled at her from across the chamber. Despite that pang of sorrow, for a moment Twilight could believe everything would be all right.
"I can't believe yer crazy plan worked, Twilight, but you were right, we really do represent the elements of harmony!"
"Indeed you do"
At that moment, a brilliant light shone over the hills of the east, visible through the ruined windows of Canterlot; the sun rose over Equestria for the first time in nearly a year. Everypony averted their gloom-adjusted eyes from the sun's new glare, but Twilight found that she could stare right at it after only a moment's adjustment, and her heart dropped a fraction—this sun was certainly dimmer and weaker than the one back home.
A glowing sphere detached itself from the sun and drifted through the window before them. Twilight's heart was doing gymnastics now—she recognized the returning Celestia even though she had only seen it once before, but the sphere moved agonizingly slowly and its brightness flickered. Twilight's automatic elation at Celestia's presence warred with her worry.
When Celestia flashed into being, Twilight's worry won. The alicorn's mane and tail hung straight downward, and her cheeks were deeply sunken. In fact across the princess' whole body slimness had given way to gauntness and visible bones; Twilight could count her not-quite-mentor's ribs in stark relief under the skin. While everypony else remained with their heads down in reverence, Twilight surged forward with a worried cry, “Princess Celestia!”
“Twilight Sparkle, my faithful student! I knew you could do it.”
She doesn't know... Sweet stars, she doesn't know I'm not her Twilight. Now, finally, Twilight's heart sank like a stone and splashed into the pit of her stomach. Shocked, she halted just shy of the alicorn and looked at her with wide eyes that were beginning to water.
Celestia watched with growing concern. She had lowered her head, anticipating and welcoming her treasured pupil's embrace, but it had never come. Instead, the filly stood rooted to the floor, staring at her in a tightly controlled panic. She put together a gentle smile for her student and asked, “Twilight, dear, what's wrong?”
Tears rolled down Twilight's cheeks. She wanted to say that nothing was. She wanted to simply hug her mentor and have everything be alright. But instead slowly, reluctantly, she took a breath and began to explain.
Twilight wished she could look away, wished she didn't have to see what her words did to her princess. She couldn't, though. She couldn't cower away and deliver this news, so she watched Celestia's frozen, stony face as she was told that her precious student and beloved sister were dead.
It was only when the tears clouded Twilight's eyes that she finally hung her head, murmuring apologies between quiet sobs—for her own self, for her fallen self, for having failed Luna, for having failed to stop Nightmare Moon, for having not come sooner, and for having not listened when she was sent off to Ponyville. Her litany was cut short by the familiar feeling of the princess' neck across her own in a comforting embrace.
“Twilight Sparkle, my faithful student...” The voice was still strong, motherly, smooth and unhitched, but Twilight felt the drops of a single tear from each of Celestia's cheeks. “...you have done so well.”
The thin, wan sunlight that streamed over Equestria was brutally honest, despite its weakness. It revealed what Nightmare Moon's night had attempted to conceal: that the land was dead. Neat, square, green patches marked the places where magic raised food for the privileged, but they were few and far between. Most of what Twilight could see from the highest balcony in Celestia's Palace was black, sickly, and rotting. Many of the mushrooms, too, were now dying, slumping into putrid piles beneath the thin sunlight.
"It's so..." Twilight shook her head, unable to even find a word for the horrors daylight had revealed.
"I know," said Luna gently, sadly.
"I will miss the ponies here, but I'll be glad to go home," said Twilight.
Luna nodded slowly. Then she inhaled deeply and said, almost shocked at her own daring, but knowing that it must be said. "I will miss you greatly. I have come to... to love you, over these weeks."
Twilight's breath caught for a moment at the word love, but then she registered what else Luna had said. "You're not coming back?"
"Not right away. This world needs me."
Twilight looked out at the ruined world below her and nodded. Some part of her was still processing "love" in rather stunned delight paired with intense dismay at the idea of losing such a thing as love in the moment of finding it, but the more rational bits knew that Luna was right. The task of restoring what the long night had destroyed was dismayingly large. Celestia could not be left to do it alone. "Will you be able to fix things?" asked Twilight, still staring at the bleak landscape.
"I think so. It will be difficult, but I will not be alone. The ponies here will aid me, my sister here will aid me, and there are allies I can call upon. The kirin, I believe will help. Perhaps even the Kudu. And there are things that alicorns can do to combine earth pony and unicorn magic that will have great effect. So yes, I think the Equestria of this world can be restored."
"That's good." Twilight dared to look away from the view and glance at Luna. She looked so strong, standing there with her hair gently waving on the intangible cosmic wind. Yet she also looked so sad. "I... I could stay and help."
Luna shook her head, staring out into the thin daylight rather than meet her eyes. "No, Twilight. One unicorn, however strong, will make little difference to the effort here. I have seen how this world has worn on you. I have seen how much you miss my sister, how much you miss our Equestria. You should return."
Twilight swallowed, then softly said, "But I'll also miss you. I think I love you too."
Luna looked at her then, and sorrow and love both shone in that gaze. "Oh Twilight... I am glad. I am very glad indeed to hear it. Yet this world needs me desperately. And you desperately need rest, and home, and the solace of familiar things."
"I guess. But still... Don't you need those things too?"
Luna sighed softly, a small, regretful smile on her lips. "Rest, home and solace would not go amiss, no. Yet I am a princess, and an alicorn, and I have a duty that I cannot forsake. I shall take great solace in mending my own past wrongs here... and in the thought of you when all is done. We shall not be parted forever, Twilight my love." Luna smiled warmly, and Twilight found her heart suddenly beating faster. "I will return when my task here is completed." She took a step closer to Twilight, her head bending slightly.
Twilight stepped closer too, tilting her head up to the tall alicorn. Their muzzles met in a kiss that was brief, but sweet and without any hint of hesitation.
"I'll cast the portal to send you home now," said Luna when they at last broke apart.
Twilight simply nodded.
Luna's horn glowed with brilliant, silvery light that grew until it was almost unbearable to look at. Then the portal appeared, the arching rainbow shimmer Twilight remembered from what seemed like a lifetime ago. She stepped towards it, then stopped, looking back.
"Look for me in a year and a day," said Luna. "And until then, be well."
Twilight groped for how to reply, looking for the words that would somehow express the tangled emotions she felt. Finally she said, "You be well too. Just... don't be late."
Then she stepped through the portal, into the undimmed sunlight of Equestria, and was home once more.