Luna had a lot to catch up on.
Having been away for one thousand years, she has missed out on a lot of changes in Equestrian society. Everypony around her was speaking quite modernized; not like she remembered. Everything was different, even the way she looked. Luna was very small, and weakened. The Elements of Harmony has not only stripped away the Nightmare Forces, but a large quantity of Luna's own alicorn magic.
Her mane was not encased with magic, and flowing with stars. She had adapted her colors of when she was a young pony, something she fondly remembered but did not miss. She thought of spells she remembered, but none seemed fitting to restore her power.
Celestia and Luna had returned to the castle, which Luna was unfamiliar with. "Sister... is this your castle? Here in Canterlot?"
"No Luna, it's our castle. I had ponies come in to put in your very own throne next to mine".
Luna looked in awe at the throne room. "I'll let you get familiar with everything. I know it's a change from where we last were when we were together. But I am sure you will enjoy Canterlot".
They stood in silence, looking around at the interior of the castle. "Luna, dear sister," Celestia broke the silence, "I was unsure of how to welcome you home. I assumed we would talk to each other, and catch up. I've missed you so much."
"I have missed you too, Celestia. I missed being along side you in our reign. It appears have missed so much in my time on the moon."
"Well, this castle has been here ever since you left. I have found new bearers of the Elements of Harmony. The 6 mares that were at the ceremony helped free you with the elements. The element of Magic is Twilight Sparkle, who I taught as my apprentice. Not much has changed other than that. Yes, society has modernized. But I'm sure you will adapt".
"It seems I have a lot of reading to do." Luna laughed. Celestia laughed along, bringing tears to her eyes. She missed this; the moments of joy with her only sister. Celestia noticed that Luna was so small, and frail. She looked tired and weak, almost like a filly. It touched her heart, knowing that the Elements of Harmony had... downgraded her sister so much.
The throne room was a dim orange as the sun was setting. Luna had been admiring the stain glass portraits that were embedded into the castle walls, allowing sunlight to seep in. "Luna, it appears it is time for the moon to rise. Do you think you are ready to raise the moon once again?" Celestia asked doubtfully.
Luna shook her head, "I am sorry sister. I am very weak, and I do not think I have enough magic at the moment. You may have to continue to raise the moon until I figure out how to restore my alicorn magic. I am tied to the moon, so maybe it will just take time for it to restore my magic".
Celestia nodded. She motioned for Luna to join her on a walk up a flight of stars and over to a balcony. The wind caught in the Princesses manes, sweeping them away form their faces. Celestia's horn glowed with a gold aura and lowered the sun, and in it's place, the moon peaked over the horizon. The glimmer of stars twinkled in her eyes, wide with awe. It has been so long since she has seen the moon rise, and the night sky in all of it's beauty.
"We must get you to bed. I know it will be a little odd at first to sleep through the night, but you need rest. I will have guards watching the castle instead of you, or I. Is that alright sister?"
"Yes, that is quite alright" Luna said softly. And with their goodnights, the two reunited princesses went to their chambers.
The next day was to be a busy one. With Luna back in power along Celestia, she would be bombarded with papers and other new duties. The Sun Princess knew it would be hard on Luna. She had addressed it to each and every guard to treat Luna with the same respect they did before she was turned into Nightmare Moon. She made it known that Luna is still Luna, no matter the differences.
Luna was awake early in the morning, scouring the Library. It had taken her a while to find it, but she did and was set to work right away. She looked through many books on magic, and spellbooks upon spellbooks. There were a few spells that were along common grounds of "how to temporarily strengthen your magic". There were none on restoring alicorn magic, considering there were only 3 alicorns in existence. Luna remembered Celestia mentioning a pegasus filly named Cadence, who found the magic of love and Celestia made her an alicorn Princess. An adopted niece, who she has yet to meet.
Alicorn magic was hard to document, since not much was documented about in in history. Even still, the blue alicorn went through many books to no avail. Frustrated, she slammed the last book shut. "Maybe I should not be worrying about this... but I still must lower and raise the moon each day." she murmured.
"Maybe that is just what you need" a familiar voice spoke softly from behind Luna.
Luna spun around to face her elder sister. "But... how? I figured maybe if the moon was aware of my presence back here on Equus it would return my magic. I am still weak, so that is not the case. I just do not understand".
"Luna, you may be right!" Celestia sat beside her sister," The moon needs to reconnect with you. Maybe, you need to raise the moon to rekindle your magic."
Luna grinned widely, "Sister, I believe you are correct! But, what if I am not strong enough?"
"We will see, and I will be here to help you".
That night, after all the work that Luna had went through, the time had come for the sun to slip under the horizon once again. Luna stood beside her sister on her large balcony outside of her bedroom. She looked up at her sister, who's horn was wrapped in a gold aura. The sun slipped beneath the dark horizon, and the sky was laid in indigo.
"Are you ready, my sister?" Celestia asked.
"Yes, I think I am ready" Luna said with a deep breath.
Luna readied herself, and her horn lit up with the familiar blue aura. She thought back to the many times she has previously raised the moon. Look for the moon, find it and capture it with your magic. She strained as hard as she could and her magic hit something. She felt the moon, and each and every little star following behind the moon. She grunted, straining herself more and more. The moon began to lift, and so did Luna.
Luna's hooves disconnected with the ground as her magic raised her up. Her eyes glowed with magic as it enveloped her. The moon slowly rose over the horizon and Luna was absorbed in magic. Stars began erupting from her horn, twinkling down onto her mane. An indigo silk slithered through her coat, darkening it. There was a brief burst of light, and Luna fell to the ground.
Celestia looked up her sister, resting on the ground. She smiled, looking upon her sister. Luna had an dark blue coat, like the sky above her. Her mane was a deep blue, flowing with stars. The sky was scattered with constellations, brighter than they have ever been.
Luna opened her eyes slowly and looked to the sky. She smiled with delight at the moon, risen high in the sky.
"Luna, you did it! And look, your power has returned... it is so lovely to see you have returned".
Luna stoop up on her four hooves. "Yes, sister. I do not feel as weak anymore. I am just fine".
Author's Note
I really didn't know how to end this, so please excuse the poor ending. 
