Celestia stepped over a soldier that looked like they weren't aware of her presence. "Day or night, some things don't change."
Luna chuckled softly at her sister. "This may be true, but none of your soldiers celebrated this so late in their life."
"That is not the accomplishment you think it is." Celestia inclined her head faintly. "Still, that you have a non-pony member, and they've gained a cutie mark? I will give credit for that. That was... a uniquely pony thing, so far as ever I have known it. Have you ever witnessed a non-pony gaining one before?"
"I consulted with the expert on your suggestion. The crusaders swear such a thing has not happened on their watch either, and they tried!" Luna raised a hoof to her chin for considerations. "Now, changelings can have cutie marks. They'd be second-rate infiltrators if that weren't the case."
With the music getting heavier and louder with each step, they resumed their walking in the direction of the room where the sound was the most intense. As the music reverberated around them, they stepped into the room that the soldiers had taken over and transformed into a place for celebration. The decorations were fitting for a cutie-cenera, which was half the problem. They had copied everything with great accuracy, making them perfect for a small foal's special day.
There was the star of the show, being swatted, laughed at, or was that with? His expression showed little a hint that he was enjoying the attention. But he noticed their arrival with a jerk, standing up bolt straight.
Others noticed his sudden attention and, like a passing wave, soon everypony there was looking at them, and the music cut off as the wave reached somepony standing near the phonograph. "Princess on deck," shouted one of them, standing in rigid formality.
Luna made a lowering motion with a hoof. "At ease." Many of the guards there were her own, to no surprise. "We are here to celebrate, just the same as the rest of you. Just think of us as two more--"
"--somewhat large," added Celestia.
"--somewhat large," Luna sighed out. "soldiers. Just here to have fun."
They did their best to obey the order to get back to enjoying themselves. Initially, the motions were quite rigid, but as time passed they began to warm up to the idea. Luna sank beside the star of the show. "Skyline, it has been some time since last we spoke."
"Hey..." He looked away and back. "Nice to see you again... ma'am?"
"Tonight, you can call me Luna." Luna gestured to the side. "This is..." She trailed off, realizing that Celestia was already wandered off to chat with some other soldiers. "That cougar over there is my sister. I swear... Let's focus on you, Skyline."
"Hello... Luna." Skyline rubbed behind his head. "Are you... Um... What are you looking for, ma'am?"
"Luna," she corrected. "I wanted to talk to you. I wanted to do that before you had this sudden event, but it made me want to talk to you even more. Allow me to ask, has this impeded your natural abilities?"
Skyline erupted into a brief flame, becoming a second Luna. "It has not," he assured in Luna's own voice.
Luna jerked back in surprise. "I see!" She glanced along the side of the doppelganger, spotting his cutie mark did not match hers. Though he had the spotted patterns of his rump down, the actual mark was his own, the compass and screwdriver. "But you can't change that."
"I can't," he miserably agreed, shrinking back to his normal form as if the extra mass were burning away from him. "Which makes me kinda bad at... changelinging?"
"I disagree." She inclined her head faintly. "Become something that has no cutie mark, and never did. Can you do that?"
Something without a cutie mark? His eyes wandered the room curiously. "What about..." With a fresh wave of changeling magic, he became a table, empty, waiting to have things placed on it. "This work?" Despite being a table, he could still talk.
Luna leaned way off around to see under Skyline examining his table-nature thoroughly. "I don't see a cutie mark. Very good. Your mark is only 'stuck' when you are in the form of a pony. Ponies have a cutie mark, and yours is pre-determined. That isn't so bad, hm?"
Skyline returned to his usual form. "Really?" He twisted to look back at himself, but he was a pony, so he had a mark, taunting him. "What if..." And he became a dragon, who could move and look without so much difficulty. He checked his rump, and it was blank. Dragons did not have marks. "Huh... But, Luna, I swear I tried not-pony forms before, and it was there! Why is it working now?" He scowled at the obvious plot hole in his own life, right where one did not want a plot hole.
Luna smiled gently, still on her belly before Skyline, putting their heads close to the same level. "It was a new thing, and, I like to think, I'm the first that brought it up. A combination of practice and actually trying."
Skyline clopped a hoof to his head. "R-right... So... It's working now because you got it in my head to try just not having one because that's normal?"
"Is it not normal for a dragon to not have one?" countered Luna with a knowing look. "I thought everypony knew that."
"Obvious, looking back..." He had panicked. He had tried to have a different mark, but he couldn't have a different mark. His mark was set. But he could... just not have a mark at all... "Wow. I feel dumb."
"You shouldn't." Luna rose to her proper height. "You were scared, not stupid, though being scared can make us do foalish things. May I remind, you earned your armor."
Skyline glanced to where the armor was secured away. "Yes, ma'am..."
"Quite rapidly, may I remind." Luna raised a hoof just under Skyline's snout. "Don't tell me my guards are stupid. Were they daft to allow this?"
"No! Ma'am... Luna." He shrank back a step. "I am ready to serve."
"Glad to hear it." She leaned in, noses almost touching but not quite making contact. "Tonight, your order is to enjoy yourself, and celebrate the arrival of this new step in your life, even if we did not invite it."
"You heard her." Piercing came in from the side suddenly, throwing an arm around Skyline's neck. "Did you hear? He got his mark for dropping the best bombs!"
Luna inclined her head. "That hadn't come up. You excelled in that course? I had thought it abandoned, truth told. It's been... quite a while, according to my sister, since the last time any guard, day or night, was called to make a bombing run. With luck, there may never come another time... But, things happen."
"Yeah, better to know how and not need it than the other way around," argued Skyline. "And that's when I got that." He pointed back at his stuck cutie mark.
Luna tapped at her chin thoughtfully. "There are other uses for precision bombing than causing damage, Skyline. There are towns in remote locations. If you can get parcels to them precisely, they would be thankful."
Skyline made a sour face. "I joined your guard, ma'am. Your guard aren't mail couriers."
"Not usually." Luna smirked softly. "In part because most of them would not be good at it. Emergencies happen, Skyline. If something direly needs to be somewhere, I may ask you to see that it happens. You would follow my order, would you not?"
Skyline cringed, put on the spot. "O-of course not, ma'am. If you told me to... I would. That's my job, ma'am."
"Luna." She set a hoof on his nose. "At least for tonight. I simply wish for you to see that mark for what it means. Being able to get things where they need to be can have a variety of uses, and you should expect me to consider them. Harmony forfend, perhaps we may even need those bombs to drop. At least I know who I would call first, should such a need arise."
"Best bomber," laughed out Piercing, having gone nowhere. "Luna! Want a drink?" Using his horn, he grabbed a glass of something colorful and brought it over. "Like you said, tonight you're just one of us! Drink up!"
Luna accepted it, the color around the cup shifting to her magic. "Since you are kind enough to invite." She took a sip and drew the cup away. "Powerful... Do you not have work tomorrow?"
Piercing shrank back a step. "Um..."
Luna wagged the cup at the withdrawing unicorn. "I should expect a number of my guards to be nursing headaches tomorrow then. Who planned this party?"
Skyline pointed at Piercing, who looked like he wished for the ground to consume him at that moment, but it offered no such easy escape.
Luna hummed softly at the abashed guard. "You clearly care for Skyline."
Piercing's blush grew worse. "It was a chance to run an adult cutie-cenera, ma'am. I never got to do that before!"
"And a very nice cenera it is." Luna tapped Piercing on his nose. "I will inform your commanders to take it easy on you, tomorrow. Unless something comes up. You know the duty you signed on for, guard."
"Yes, ma'am!" He saluted sharply. "Sorry, ma'am."
"You've avoided me." She pointed at him, then Skyline. "What do you think of him?"
"Huh? He's a soldier, ma'am! A kin! The bastard got ahead of me... I thought I'd get the armor before him, ma'am, and he snuck out ahead of me!" He stomped as he vented his frustration. "I'll catch up, ma'am!"
Luna raised a hoof to poorly conceal a snicker. "You're already tipsy, guard. Piercing Thought, wasn't it?"
"Yes, ma'am!" he crisply responded despite any fuzziness in his thoughts.
Luna looked back to Skyline. "I meant to ask... Are you enjoying your armor?"
"I... technically don't need it, ma'am." Skyline rubbed behind his head awkwardly. "I can be that when I want to be." With a wave of flames, he returned to his bat pony form. "So--" He found Luna's hoof on his nose, a habit of her's that night. "Ma'am?"
"The armor is a uniform. I was told you can assume clothing as well, so at least look the part. It won't look right if one of my guards is without the armor that every other member of my guard wears." Luna drew her hoof back. "I understand you don't 'need' it, but it is the uniform. You'll hardly be the first pony to wear a uniform despite not 'needing' it."
Skyline worked his wings in a fidget on his back. His voice lowered to a conspirational whisper, "Do I have to wear it every time I go bat pony?"
Luna rolled her eyes. "Actually... You are performing a service for us. While you are off-duty, being seen as that deflects some of the questions that may otherwise arise... Such as why nopony sees my night guards going about their--"
"--Do ponies ask about that?" blurted on Piercing, rejoining the conversation suddenly. "I always wondered..."
"Rarely, but not never." Luna rolled her eyes at the interruption. "So, again, off-duty? You can wear what you like, that includes your form. So long as you're not imitating a specific living pony, you're not breaking any laws. On the other hoof, there is almost never a good time to look like me, so don't do that again. Hm?"
Skyline colored at being called out for that. "Sorry... I was just--"
"--I understand," cut in Luna. "Just not again. I know a changeling must see identity as... something different, but we other creatures see our reflection in the mirror as something very special. Having something else with that is quite... uncanny. Now, they appear to be engaged in some manner of frivolity. I would ask that you show me how to play."
"I got this." Piercing pushed forward. "This'll be fun! Luna vs Skyline, everypony wins!" He cheered out and led the way towards the others.