Luna was many things: the regent of the night, a former villain, an avid gamer, and a hopeless romantic.
One thing she was not, however, was an evening pony.
Luna drowsily rose from bed, working out the kinks in her back. Her sister's sun was about an hour from setting, which gave her plenty of time to enjoy a hot bath and polish her accessories as she tried to wake up fully.
Eventually, the time came, and Luna stepped onto her balcony. She nodded to Celestia, who was stepping onto her own balcony about a hundred yards to Luna's left, and their horns lit. After a moment, the sun lowered and the moon rose, bringing forth the night.
Luna lingered on her balcony, staring forlornly at the moon. A thousand years, and she couldn't remember a thing about her time there. And yet, every time she looked at that rock in the sky, there was a faint nagging feeling, like she'd forgotten something important...
Just as she was about to head back inside, a small light caught her eye. It was coming from the direction of the moon, and headed this way fast. Luna jumped out of the way just as a glowing something whizzed by her and landed heavily onto the balcony. After a moment, the glow stopped, allowing Luna to get a look at whatever had just crashed.
It was a stallion — an Alicorn stallion at that. His fur was that shade of brown that good copper was; his (literally) flowing hair was a purple that deepened as it went down, splotched with yellow starbursts, and overall reminded her of the dusk sky; his chest was covered by a navy blue vest decorated with dark brown pockets and a moon emblem held in place with brown straps; his hooves were covered golden starburst-shaped shoes; on his face was a dark purple mask with two blue moons on the ends; his ears were adorned with crescent moon earrings; and his Cutie Mark was his mask seen from a side-view (showing the moon shapes prominently).
There was something about him that she found familiar, but she pushed that thought aside. She lit her horn, ready for anything he might try, and stepped forward. When her shoe clicked on the stone balcony, his eyes shot open. She tensed herself, but he got up, not even seeing her, and looked over the balcony.
"I did it..." he breathed, then pumped his hoof. "Woohoo! I did it! I finally got off that stupid rock!" He wound down his celebrations, and took a breath to calm himself. "Now all I need to do is find Luna."
"And what?" Luna interrupted, causing him to turn around in surprise.
"Luna!" he exclaimed, attempting to rush over to her. He stopped, however, when she pointed her lit horn towards him. "L-Luna?"
"Not another step closer, masked stranger," the Princess warned.
" 'Stranger'? Luna, it's me, Cosmic Masquerade!" He took off his mask, leaving his concerned silver eyes exposed.
That name did spark some odd feeling in her chest, but nothing concrete. "I do not know anypony by that name."
He reeled, as though struck by a blow. "Y-you don't remember me? We've known each other for 998 years!"
"I spent the last thousand on the Moon," Luna pointed out.
"I know that!"
She blinked. "So you're saying that I met you... on the Moon?"
"Yes!" Cosmic exclaimed, becoming a little exasperated and a little pleading.
She frowned. "Excuse me if I find it hard to believe that I met a pony on the Moon."
"But I'm not a pony," he said casually. "This is just the form I choose to use."
Luna raised an eyebrow. "Wait... if you're not a pony, then what are you?"
"I'm a Moon Spirit." As soon as he said this, his body began to lose its form as it became more nebulous. It lost all of its color, becoming a dark night's sky with shimmering stars in it. The only thing that remained were his eyes (which were now entirely silver) and his mask.
Luna was struck by how similar this creature looked to the Tantabus. She reflexively shot out a spell, but his nebulous body parted to dodge. He regained form, turning back into the stallion...
Only this time, he was starting to cry silver tears. "Y-you really don't remember me, do you?"
She shook her head, and that tipped him over. He leaned over, sobbing quietly.
What the hay was going on? A stallion from the Moon crashes on her balcony, and starts crying when she doesn't recognize him? She'd seen some odd things in her day, but this took the cake.
Seeing him so sad sparked some sympathy in her, and she carefully stepped forward. When he didn't react, she continued cautiously until she was standing over him. She laid a hoof onto his shoulder and said, "I, um.... I am sorry if I've upset you."
He shook his head, drying his tears. "It's not your fault. You said this might happen, but I thought that, with all we've been through..."
Luna frowned. "Another thing I don't understand is how you seem to know me, when I was Nightmare Moon for the past millennium."
He pointed to his mask. "This mask allows me to see anypony for what they really are. Helps a lot when your species can shape-change."
Her eyes widened. Even while she was Nightmare Moon, he could see her for what she was? Even while she was Nightmare Moon, the magic of the mask still saw her as Luna? It was touching in a strange way.
She sat down onto her haunches next to him. "Cosmic, was it? Would you like to come in for breakfast while I think of what to do?"
He sniffled a little. "I've never really tried Earth food before... but I wouldn't want to impose...."
Luna shook her head. "Nonsense. The Royal Chefs already prepare more than we need to eat; we wouldn't want all that food to go to waste, would we?"
He smiled a little, looking up at her with what seemed to be admiration. "I guess not."
"Wonderful. Then let's show you to the dining hall." She helped him up, and led him into the hall.