When one went to the place that they would call home, there was hopefully a feeling of familiarity that would come with that arrival. But for Luna, there was no such fortune. Canterlot didn't even exist back before she was sealed away in the moon, and now, here it was. A sprawling city of grandeur and elegance. A place she had been brought to, so soon after her return, to now call her home. Uncertainty was all over her expression as she finally entered the royal palace, an impressive structure to be sure, but one that nevertheless felt strange and alien to her. Celestia was with her the whole time, naturally, and the elder sister maintained that look of happiness she'd had ever since her sister's return to her side. There were other ponies here too, and many looked on in awe at the newly-returned Princess of the Night. None had ever seen her, and none had ever even heard of her until today. Yet here she was, being greeted in much the same way as Celestia would have been, with bows and smiles aplenty. Luna did her best to act as regally as her station demanded of her, walking with grace and her head held high. Yet when she spoke, it was with the barest whisper of a voice. "We are...grateful that they are being so welcoming."
Celestia smiled to her, and after a while she stopped walking, with Luna following suit shortly afterwards. The older sibling took a deep breath, then reached out to gently place her hoof upon Luna's shoulder. "I realise this is a lot to take in, sister. Much has changed in the time you've been gone. But I promise you, I will be there every step of the way to aid you in your recovery."
Luna smiled, grateful to her sister's openness and warm feelings towards her. But ever there was that doubt, that uncertainty about her being here, and they were indeed feelings she was willing to speak up on. "It's just...all of this is...new."
Celestia nodded, glancing around their current surroundings. "The old castle had...too many memories. And besides, I felt it would be better for me to be among those we watched over, not far away and unseen."
Luna grimaced. "We have been unseen all the same though."
A solemn look on Celestia's part, as well as a deep sigh. "I know. But Equestria was never as right as it was when you were by my side. The nights, not as beautiful. The dreams, not as safeguarded."
Concern came to the younger sister. "Hast thou not been fighting against the nightmares, sister?"
Celestia looked to her with a look that could only be described as disappointment, but when she spoke it was clear that such feelings were directed towards herself, not Luna. "I tried so hard to do what you did over the years. But I was never as skilled in the dreamscape as you were. There were always a few nightmares getting through, plaguing the slumber of the ponies. And...it broke my heart every time I failed them."
Luna could see, in this moment, the dropping of the regal mask Celestia had so often worn in front of others. Where once there was a proud dignity, now there was a melancholy to her. In one moment, a thousand years of worry and care were as plain as day on her, and Luna, despite her own hardships over the last millennium, approached her, looking to her with sympathy. Celestia looked back to her, seeing her smile as she spoke. "It's alright, Tia. I'm back now. And I promise you I will resume my post as well as I can."
Celestia gave her a look of concern. "Are you sure? There's no shame if you want to rest first."
Luna shook her head. "Thy words are appreciated, but...a Princess must do her duty."
Though hesitant, Celestia soon relented, giving a slow nod to her younger sibling. "Very well. I will go ahead and have your chambers prepared."
Luna tilted her head. "Chambers?"
To that, Celestia's own smile returned. "You might not have lived here before...but I have always had a room ready for you...for the day when you would come back to me."
Luna looked to her sister with fondness, which Celestia was sure to return, before watching her turn. Several guards went with her, and as Luna stood in silence she awaited the moment when she was, at last, alone. That moment came when Celestia was finally out of view, and before long the younger Princess turned to head towards a nearby balcony. But instead of excitement at the thought of resuming her role, or perhaps worry at getting back into it, there was a look of guilt to her. For she had seen something that Celestia had not, and had said nothing about it. Now she knew she would have to address it, and as she exited onto the aforementioned balcony, her gaze drifted upwards. The night sky was always beautiful to her, as befitting of one for whom it was their domain, but there was something else up there that held her notice. Four twinkling stars, shining brighter than all others. Stars that moved. Stars which, as Luna watched, drew nearer. "It is alright...we are here now," she spoke softly.
As if that was all they needed, the stars did indeed approach. No other pony saw them, for this was hers and hers alone to do. The balcony shone bright as they came closer, and Luna held her gaze firmly as, one by one, the stars descended upon the marble floor before her. These were not giants of burning gas like the sun, but great forces of light which illuminated all around them. Shining and beautiful. And now, that light dimmed, revealing shapes behind them. Shapes that Luna knew all too well. Hooves and wings and horns. The shapes of ponies, bright white all over. Ponies who now bowed to the mare in front of them. "Hail, Princess Luna," they all spoke together.
In response, Luna smiled, giving a similar bow of her head. When she looked up to them, they were still kneeling in reverence to her, awaiting her words and her commands. Luna sighed at the sight. The one they knew had wanted so many things. Things she no longer wished for. Yet here they were, so far above mortal ponies, and utterly devoted to her through the long years. She stepped forward, leading to the four standing tall, expecting her to speak. And speak she did, though it was with a calmer tone than they were perhaps anticipating. "Achernar...Belel...Yildun...Zibal...long have you served me. Long have you journeyed to free me from my prison." Her smile returned, if only for a moment. "I truly appreciate what you did. In ancient times you vowed to serve me in all things, to be the guardians of the night, tasked with scouring the cosmos at my behest. You have performed your duties well these many years, and for that, I am eternally grateful."
Again, the four ethereal ponies bowed, with one of them, the mare Belel, speaking softly. "It has been our honor, my Princess. The night is yours, as are we, and forever shall we serve. Though vast distances lay between you and us for those centuries, we managed to find you, and free you. Now you can reclaim your place as ruler of the night."
A wince from Luna, and she turned, not wanting to look them in the eye. They didn't know, she told herself. Everything that had transpired since she last saw them was completely unknown to them. She knew she would have to tell them, but the thought of it gave her no joy. Honesty might indeed be one of the most valued traits among her people, but that didn't make it easy. So, taking a deep breath, she stood tall, wings outstretched, and spoke with as much of a presence as she was able to muster. "My followers...my friends. Much has happened since last we met. And for your loyal service you deserve to know the truth." They looked to her, confused and uncertain, which definitely didn't help Luna's feelings on the matter. "In the later years of my time as a Princess...we erred. we...strayed." She grimaced, then continued. "We were not the benevolent leader you believed us to be. We allowed darkness into our heart...and we fell from grace."
One of the stallions, Yildun, stepped forward, shaking his head. "No! That cannot be! You would never do such a thing!"
Luna stared at the ground, shame at her past actions returning to her. "But we did, Yildun. Jealousy, envy, rage at feeling unappreciated. These things and more swirled like a tornado in our very soul, and where once there was Princess Luna..." She frowned. "Nightmare Moon rose instead. A wicked mare of darkness who sought to dominate by covering Equestria in eternal night. So great was our fury that...that even Celestia was hurt by it." She turned again, looking towards the palace, with her back to her followers. "Our actions...were not those of a leader. They were not those of a guardian of ponykind. They were...the actions of a monster. And we paid the price for it." Slowly, she resumed looking to her fellow ponies of the night. "We thank you, friends...but when you freed us, it was that monster who returned to this land, not we."
Instantly, the other ponies got to their knees, showing not only their prior reverence, but also doing so out of a clear attempt to prostrate themselves. "Forgive our transgression. It is small comfort, but...we did not know," one said.
Luna shook her head. "You are to be commended all the same. No other would have been as faithful." A thought came to her, and she stepped forward. "For your many years...we grant you leave. No longer are you under any obligation to follow or obey us. You may go, live whatever lives you seek, to be free of us and the duties we placed upon you."
Looking up to her, the four ponies then glanced to one another, uncertainty as clear as day upon them. They shared no words with each other, yet a thousand words and more were known all the same, and in the end they stood, looking to her firmly before Yildun spoke a second time. "No words can ever express the appreciation we have felt for you, my Lady. You have been our leader, our idol, for our whole lives. You grant us freedom? You grant us life beyond our duties? We thank you for that too. But know that...if it is our wish...that we will continue our charge. We will patrol the night skies, we will fend off the horrors that lurk in the dark, and we will carry the name of Luna to every corner of the cosmos."
Luna didn't know how to feel, only that she was overwhelmed by the devotion and loyalty that was being shown to her. Though she tried to fight it, a single tear began to form in her eye. "It is, even after so long, a lonely existence."
Yildun smiled again. "No longer...for you have returned to us, Princess."
Slowly, Luna smiled, giving a quick bow of her head. "Very well...if that be your choice...then know that we are proud. Go then. Fly to the skies, fulfil your duties...and know that we have faith in every one of you that ponykind is all the safer under your watchful eyes." Again, her followers bowed, and in unison they stood tall afterwards, stretching out their wings and launching themselves up into the heavens. Luna watched for as long as she was able, seeing them fly further and further away, until they were yet again little more than four twinkling lights among millions. A smile came to her, and as she let out a deep sigh, she spoke softly, not knowing for certain if they could hear her. "Thank you...for my freedom."
Author's Note
One more from the "early fanfics that got deleted that one time" pile 
And for those who are wondering, the names of the star-ponies were taken from real-life stars after a quick Google search on my part.
