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// Celestia got banished away after becoming some kind of Nightmare instead of Princess Luna. 
// Story: Bits and Pieces 
// by Author-Man 
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They say that hindsight is twenty/twenty. But it remains baffling to me that nopony saw it coming. You see, all suspicion fell on Luna, which I suppose is understandable. Even putting aside the association with darkness and her habit of lurking in the dreams of children - something that most ponies were naturally suspicious of - Luna was outspoken, capricious, and prone to fits of violent rage. All eyes were on her - her jealousy and her loneliness, always dancing on the edge of madness but never quite falling off the edge. Of course, nopony actually thought that the obvious solution was to move past their petty fear of her and give her the attention that she craved. They merely watched her from afar, waiting for her to inevitably snap. And then one day she did, and something no one had expected happened.

Because not one of those fools had thought to pay any attention to the other princess.

Being the ruler of a country is stressful. Once upon a time, Celestia and Luna had shared their duties, ruling equally. But, over time, Luna's jealousy and loneliness had caused her to withdraw more and more, and more and more of the work of running Equestria had fallen upon the elder sister's shoulder's. The politicians were far too busy anticipating Luna's descent into madness, leaving even more work for Celestia, until it came to a point where her every waking moment (and a significant portion that should really have been spent sleeping) was dedicated to the running of Equestria.

It's only natural that eventually she snapped.

It's a matter of historical fact that, one day, Princess Luna decided to simply not lower the moon. It is unknown how the conversation went, but I like to think that it went something like this;

“I am no longer going to lower the moon!”

“I noticed! I've been having to do it myself while you moped in the corner for the past year!”

“No, I mean I'm... Look, eternal night! That's what I mean!”

“What. Okay, fine then, eternal day. See how you like that, you lazy shit.”

… wishful thinking, I suppose.

This went on for several hours, the two sisters arguing back and forth. Luna raged about the fear and resentment the ponies treated her with, and the crushing loneliness she felt every day. Celestia complained about the massive workload and the ungratefulness shown to her. Their argument got progressively more heated, until both sisters decided to resort to brute force.

The sun and moon hung in the sky, together, for approximately three months. Each sister attempted to force the other's chosen celestial body below the horizon. Neither succeeded.

This is the point where things get difficult. We know that both princesses transformed into hellish Nightmares. Perversions of what they once were. Where Celestia was once kind and wise, she became viciously violent. Where Luna was once just and honest, she became maniacal and sinister. We also know that their argument escalated from holding the sky hostage to an actual magical duel. But records are scarce because, naturally, there are no primary sources; everyone who wasn't Celestia and Luna was busy running for their lives.

And then, just like that, it ended.

Celestia and Luna vanished, never to return.

No one knows why they vanished, or where they went, but there are theories. Some believe that the two of them ended each other's lives. I find this doubtful, myself - until then, all evidence pointed to them being immortal, or at least very hard to kill. Still, if anyone could kill Celestia, it would be Luna, and vice versa. Another, somewhat less credible theory is that whatever created them returned and put a permanent end to their bickering. It's a nice idea - very mythological. But there is absolutely no evidence to back it up. And then there's what I believe. I believe that the Elements of Harmony, Equestria's greatest weapon and the tools the sisters used to defeat Discord and King Sombra, turned on their masters in order to protect us. I know, not that much more plausible than them being given a cosmic time-out, but it's somehow comforting. To think that the Elements of Harmony watch over us. Naive, I know, but it's what I believe nevertheless. Still, we'll never know for sure. Not unless we go back in time and find out firsthoof... and probably get killed in the crossfire between the two sisters.

If it's alright with you, I think I'm good not knowing.