On the beginning of the fourth day after King Sombra’s defeat, Luna returned.
She looked out over the vast expanse of emptiness, of nothingness where once stood a mighty empire and shook her head slowly. It was hard to believe that there had once been a thriving city here. A city supported by surrounding lush, verdant fields of crops enjoying the protection from the harsh cold by the once-good king and his magics. Once grand, now fallen.
And now it was all gone.
The wind blew Luna’s mane into her face. She ignored it. Celestia hadn’t wanted her to go. She had asked the last three nights when Luna was going to bring the moon and stars back. Tight-lipped and withdrawn, the only time the Princess of the Moon showed a reaction was when her sister placed a comforting hoof on her withers and said, “Don’t worry about it, sister. I will take care of it tonight.”
Luna had said, “No, please do not. This is the only way I can mourn him. If I must suffer a loveless, eternal life, than this world can suffer a few dark nights as a memorial to what I have lost.”
Celestia opened her mouth to tell her all was not lost, that though rare, perhaps one day a male alicorn would come and replace the hollow space left in her heart by the now fallen king’s absence, but one look into the sad eyes of her sister made her reconsider. Now was not the time for such hopes, not while she was still mourning a love she would never have. You never forget your first love, she recalled her ponies well-known saying. A life immortal took almost as long to forget such strong feelings as the entire lifespan enjoyed by her subjects, but to such radiant, eternal beings, it felt no longer. It was, however, just as painful - mortal or no, they shared a universal truth - the deeper one loved, the deeper the wound when left behind.
In the meantime, the court officials kept asking what was wrong with Luna, why the moon did not return, why the nights were shrouded in absolute darkness? All Celestia could say was they were mourning the passing of the Crystal Empire - the source of love and light to Equestria, which of course, was in part, true. That seemed to satisfy them, but each night, they grew a little more impatient until last night Luna had heard talk among the officials of how angered Celestia had become, her eyes flaring in heated rage and had commanded, “Do NOT ask me again! They will be back when they will be back!” She had stomped her hoof, sparks flying against the polished marble and then turned and left without another word.
At this point Luna was so withdrawn she did not notice before then that her sister was receiving pressure from the court. All this had been about pressure, duties, responsibilities, the heavy weight of the crown that even though so physically light, had crushed her soul and spirit as she had watched her lover fall to a curse that never should have been his burden to bear.
The winds subsided and Luna managed to put her hair back into place. She in truth did not care, but out here there was literally nothing else to do, nothing else to see from horizon to horizon. All was bleak, empty.
All was gone.
She searched around for a mark she had left in the ground before they had left and after the empire had vanished. It was the spot where Sombra had lain defeated, where she had cradled his body, waiting for death to take him, her tears peppering the ground around them, her teal eyes pleading him to put aside his foolish pride, to come back to her. She had seen much in that hellish, green-tinted glare overlaying his red crystal eyes - pride and the power that had consumed the stallion she had once so deeply loved.
No, still loved, she had realized when he had so calmly, so clearly declared that the covenant of their love was the only thing he would honor above all else, the one thing he would take to his grave. She had clearly seen that in his eyes, too, and the pain of thinking she had betrayed that by not standing with him against her sister. That had been the vestiges of his mortality still clinging to his ascended body and shattered mind, incompatible with both his kingly vows and his sanity, torn apart by an amulet’s haste to accelerate the ascension, bypassing the wisdom needed to keep that mind intact.
Luna sighed, looking around. It had to be here somewhere...ah, there it was. The crescent moon-shaped hoofprint, validating that the memory of what she had been through had not been a dream, only a waking nightmare. She knelt to it. “At least you are still here,” she said to the hoofmark. “And beneath here, somewhere under a hundred million tons of ice, buried so deep I cannot sense you, you slumber. You wait.”
“I went to Starswirl as soon as we got back to Canterlot,” she told what lay beneath the unhearing layer of permafrost underhoof. “He did his divinations,” she shook her head. “I swear that pony has connections in Tartarus. Even Celestia daren’t ask him where he get his answers.” She looked up to the sky, noting it was getting close to sunset and hence, moonrise. “A thousand years, he said. A thousand years I have to wait for you to come back to me.” Luna lay down, her head to the ground, her lips just over the crescent, as if getting closer might just carry her words to him through the icepack. “I marked it on my lunar calendar. And in the meantime I will keep asking that crazy old pony - Is there any way to reverse the curse? Is there any way to cleanse your soul of darkness?” Her breath caught in her throat, tears soaking the snow. “ Is there any way to bring you back to me?”
Luna...
Her ears perked up and the Moon Goddess shot up, back onto her hooves. The sound, a soft, errant whisper of wind, pitched low and musical, a heavy stallion’s baritone that was familiar, tugged at her heart, threatening to stop it with painful longing. She closed her eyes, whispering his name, letting it carry on the same winds…
Sombra…
Pausing a moment longer, waiting for a repeat of the sound that never came, the blue alicorn rested a hoof lightly on the crescent hoofprint, infusing it with lunar magicks that would allow her to find it in future years again.
And again.
And again.
A thousand years was as nothing to them, yet she feared all those nothings would be laced with the deadly, sweet poison of her unrequited love for the grey stallion that lay paralyzed somewhere deep below in shadow, far beyond her reach.
“Sleep well, my beloved king. I will be here when you return.”
The sun was at the horizon now, waiting for her. Princess Luna stretched her wings, ascribing arcane symbols in magic circles around her to aid in her flight and her raising the moon. She took off, a graceful arc of moondust following her ascent, falling to the round sigils left behind, highlighting them after they faded. They touched off a spark that ran their curves quickly, glowing a brilliant blue briefly, then sinking into the ground, traveling deep, conducted by trapped water particles in the glacier. Somewhere deep below, they touched something new, something not there before when the glacier was young, sinking into it, leaving a restful, peaceful slumber behind deepened by her presence, by her love. A love that said, “Rest easy, my beloved. I will be here when you return.”
The surface of the land returned to its pristine, white state, the heat of the magics melting the snow, erasing the sigils, the winds solidifying the puddles back into ice that reflected the newly risen moon and stars above them.
Author's Note
Did this in one night from notes I dictated into my phone while going to work. Once I hit the keyboard, it was banged out in less than an hour and a half. Seriously, the cover took longer to create.
Already working on a sequel, but please request it in the comments and you'll make me smile 
