Your solar eyes are like nothing I have ever seen.
It was a part of daily life, as the rising and falling of the moon and stars were to Luna. Not as frequent as the passing of days, but just as necessary. Overheard a team of pegasus moved, swift and sure as the wind itself, coaxing clouds into their right position. Luna observed their movements from beside one of the parapets of the castle, where she often spent her time alone.
"I hate when it rains." Celestia muttered at her side, surprising Luna with her candor. It was only in the presence of her sister that the elder Princess was so open with her thoughts. Never was she a liar to the people, but in public Celestia was more diplomatic in her assertions.
Luna liked this Celestia, alone in her company. In these times, she could steal the mare from her people. Keep her as her own and just pretend they were fillies again, revelling in the company of one another. In those days they used to roll and play with one another in the tall grass – rain or shine or darkness, regardless.
"And why is that, Sister?" A frown quirked the corner of Luna's lips as she cast a sidelong glance at her sister.
Those had been the days. Luna could still recall them with clarity, as if they were days, not centuries ago.
Celestia's eyes were mournful as she looked up, ashen clouds reflected on their surface. "It just reminds me." She muttered, as if talking only to herself.
They all had their moments like these, yet Celestia had to repress them. To the crowds she had to embody her sun – to be strong and proud and radiant. Every morning she had to get up and shake off the heavy cloak of night that gave her some peace, some respite, and face the day.
Nothing gave Luna more comfort than knowing she was the one to provide that to her sister.
Nopony else mattered between them. The ponies of Equestria came and went almost as quickly as the seasons did. Celestia had commented once that it was all those years spent inside the moon that had given Luna this bleak view of death, but they both knew it had always been there. With how much she experienced it, Celestia never could quite face it. On the inside, Celestia was as optimistic as sunshine. Clouds always came along to mar her view.
Their parents had passed before they'd even gotten their Cutie Marks. They both came to see that that was their passage – that was their beginning.
And whilst the pair mourned, Celestia aloud with muzzle buried deep in Luna's mane, the sun and moon came to intercept one another. Behind the moons darkness glowed the sun, as fierce as ever. Upon their flanks had then come both marks, and from that moment on Luna knew she was going to be that darkness.
"It reminds me." Celestia began again, the wind picking up and tossing her mane against its natural cadence. "Of how far we can fall." Her muzzle bore an upwards slant, searching the skies for answers.
Being that darkness wasn't so bad, though. Luna could be that shelter to her sister, the shadows in which she could hide – the background against which she could shine. It was Celestia's empathy that always made her a ruler more fit than Luna. Luna was logical, she was analytical, realistic. Celestia took chances, she had hope, she was kindly and understanding.
In Celestia there was sunshine, and it would never leave her. Darkness would never grow to consume her, as it had Luna. There would always be a morning after, no matter how dark the night got. It was Celestia's burden to bring that day forth, but even after the hardest of nights, Luna could see the light in her eyes.
The rain was Celestia's time to mourn. It was her time to let that darkness rush over her, all of that fear, regret, and worry. She could scream and a tempest would rise to carry her words away. The rain would track paths along her strong muzzle, and nopony could say there were any tears there. Even in her moment of breaking, Celestia looked infallible.
"If you fell." Luna's voice carried to her sister over a sudden rush of wind. "I would catch you."
And then the rain fell.