Luna slowly breathed out, almost in time with her sister. When she opened her eyes, the warm light of the sun had faded and the moon stood in its place, stars beginning to twinkle in the firmament, one by one.
"Well, good night, Luna," Celestia said with a relieved sigh as she turned to leave the balcony and head to her bedchambers.
"Rest well, sister." Luna stood in the open air for a bit longer. She liked watching the stars expand across the sky. It wasn't time for her to observe the dream world yet, most ponies were still awake. Sometimes she would wander the halls at this time, or go for a fly around the grounds, but tonight she felt like just staying here and enjoying the cold breeze.
For a while she stood there, before she finally decided to turn around and head inside. But she was only a few steps away from the balcony and around the corner, when a sudden yelp caught her attention, followed by a crash and the fluttering of something in the wind, then a quiet groan.
Quickly, she came back around the corner to see a grey pegasus, sprawled out on the balcony. A brittle part of the railing had broken and the crumbled stone surrounded her, her eyes rolling dizzily in their sockets. The bag she was carrying had slipped free and a small fortune of letters and scrolls had spread out over the space.
Luna galloped over and quickly looked out into the night, searching for any reason for the crash. An aggressor, a beast, even just an out-of-place storm cloud. But nothing stood out to her, and so she turned her attention back to the mail pony, who was starting to pick herself up. She shook her head and one of her eyes looked up at the princess, the other slightly off.
"Oh no. I'm so sorry." She stumbled to her hooves and winced, lifting one of them off the floor again. "I'm sorry, I just--oops!" She backed off, lowering herself into a clumsy curtsy, at which point her dock bumped into the other side of the railing.
The corners of Luna's mouth cracked into a smile, but she composed herself quickly and let the silent chuckle instead escape through her nostrils as a quiet huff. It wouldn't do to laugh at her. "Thou hasn't done wrong, t'was evidently an accident. And yet, why dost thou fly thy deliveries in the dark? And why here?"
"Oh, uh..." The pegasus tilted her head. She folded her wings, but one of them didn't fold all the way and hovered over her side awkwardly. "I have letters for the castle staff. Some...where..." She looked disheartened as she began to search the letters scattered around. It wrenched Luna's heart with pity. "But I, heh, got a little lost. And now I'm so late..."
Hoofbeats came down the hall and two guards rounded the corner. They didn't brandish their weapons, but they looked stern enough to make the pegasus wince at the sight of their dark armour. "Princess! Is anything amiss, we saw somepony flying in this way!"
Luna turned halfway and extended one wing behind the startled mare. "'Tis no aggression at play. But there is need. One of thee shalt call a healer to our chambers, the other gather up this correspondence and have it sorted."
Derpy - she finally introduced herself on the way to Luna's chambers - accepted the princess' generosity with no complaint, but was still profusely apologetic and evidently embarrassed about the situation. Luna watched with slight concern as she limped beside her, but felt that extending a hoof directly was not sorely needed and perhaps a bit too intimate.
She provided a cushion for her and sat by her side as they waited for the healer. The other guard came back first, all letters stacked back in the bag, then left again with the ones meant for the staff. More apologies and embarrassed gratitude followed.
"I've really done it now," she finally said quietly, looking down at her injured hoof. "I knew I should have stayed on office duty."
"Mistakes are inevitable," Luna said, hoping to sound sagely, "But thou hast not failed in thy duty. The letters have reached their recipients."
Derpy laughed sadly, but her smile was surprisingly strong. "Yeah. I always get there eventually. Though, maybe I'm not getting anywhere else soon."
There was a knock on the door and Luna called the healer inside. He took some time to inspect Derpy's injuries, before concluding that her wing was only bruised and she'd fly again in the morning with some rest, though her hoof was sprained and would need more time.
"Perhaps she should rest in one of the--"
"Thank you. We appreciate thy council and apologise for waking thee this night." Luna's quiet but firm interruption didn't leave much argument and the healer excused himself again.
Derpy watched him leave, before looking up at the princess, uncertainty in her expression. Luna wasn't used to the comforting spiel, the way her sister was, but something about this pony awoke a protectiveness in her. More than a duty, but a desire to ensure that she was safe and protected.
"We will see to our duties soon. But we will not leave from here. Thou should rest thy body and take comfort." Her smile was uncertain. She tried to mirror Celestia, but she could not see her own expression. Did she radiate a maternal calm, or did all her second guesses read plainly on her face?
"Thank you, your Highness." The pegasus' smile, by contrast, was possibly the most serenely wholesome expression she had ever seen worn by any subject. And without hesitation, she settled on her side, her bruised wing carefully extended, and closed her eyes.
Luna sat in silence for a while, until the soft, even breaths of the mail mare made her certain she was asleep. Perhaps she aught to make sure. Just for a moment. She closed her eyes and let herself sink away into the realm of dreams, already latching onto Derpy's string of consciousness.
Derpy tended not to remember her dreams. If she did, they were scraps and feelings she could only make sense of half the time. But this night, she remembered with surprising clarity. It had been hectic at first, a panicked dash away from something. or towards something? But soon, she was enveloped in a bed of warm, dark feathers. And when she awoke, the princess was still right next to her, just like she had said.
Her wing still ached a little bit, but she beat them a few times and didn't find it hard to endure. Gliding part of the way, at least to the station, and take the train back to Ponyville would be fine, as long as she remembered not to land on the sprained hoof.
When she left, she still wasn't sure how to engage with the princess. Her presence was commanding, but she also seemed to reject overt formality. So she left it at another heartfelt thank you and a careful curtsy before making sure she had her mail bag and her hat, then left the castle from the balcony where she had crashed.
She found herself staring out the train window, her thoughts drifting always back to the princess. Her elegant movements, the protective wing draped over her. That dorky smile.