Once upon a time in the magical land of Equestria there lived three alicorn sisters who used their power to bring prosperity, peace, and harmony to the land they ruled. The eldest, Celestia, used her magic to steady the sun, bringing it forth when the day began and letting it sink below the horizon when the day ended under her guidance.
Next was Selena, the middle sister whose power governed the North Star to aide the navigators in the world below and prevent possible celestial catastrophes.
The last princess was but a filly, protected by the steadfast shadow of her selfless elder sister while the benevolent and doting Celestia acted as her mentor, training her for the day when she would one day take over Selena's secondary duty: the guiding of the mysterious glowing moon, its ivory light defended against some of the subtler foes of darkness in the minds of their subjects.
The two sisters ruled wisely, nopony opposed them for it was these three who wielded the Elements of Harmony. Celestia and Selena holding their littlest sister aloft between them as their sorority and friendship ended the tyranny of Discord.
...
And it was so that for many centuries Celestia and Selena ruled along with the assistance of their junior, the playful and carefree Stellaluna.
Yet this did not last forever. Young Stellaluna was secretly very worried. Would she ever be as competent as her elder sisters? This was the constant thought that nagged her innocent mind as she strode through the enchanted forest encompassing her castle home. She did not know that she was being watched by a most desperate and malicious phantom who sensed her anguish.
Preying on her innocence and hungering for a host to puppet, the creature emerged from its woodsy cover, drifting clumsily into the path of its prey.
Stellaluna gasped as she watched a cluster of sparkly blue mist float pitifully in front of her as if from nowhere.
"Art thou well?" The princess asked, puzzled and unsure if such a being could talk.
'Poor filly, lost filly,' it crooned. 'Scared filly. Will thou ever amount to as much as thine sisters?'
Stellaluna gasped, clearly frightened and shaking. How did it know?
'I know because I am a Night Terror, a demon-in-the-dark hiding right under your muzzle! Ahh, but with your most helpful assistance I can become a Night Mare!'
She was paralyzed then, her own fear claiming her wits, helpless as the demon pounced.
...
The being who was known by no name hurtled through the forest toward the castle, possessing the form of a blue filly, a princess with turquoise eyes as it enjoyed total control and was gradually altering the young alicorn's form to suit its own needs.
The famine it had experienced for so long was gone, there was now a host!
But its hunger was endless, craving even more fuel and it knew exactly where to go for power.
The blue filly with eyes now foreign to her own face and fangs-the first of many changes-grinned maliciously.
The 'Everfree Castle' mentioned in almost all of the filly's memories would be just too perfect.
...
Selena, the adolescent paced the width of the empty throne room on her too-long legs, fretting about the location of her younger sister.
She should have been home by now! Selena thought, tucking a few strands of pin-straight purple mane, ignoring its faint shimmer. Unlike Celestia nothing about Selena was elegant or grown into-including her mane and tail which dragged behind her.
Unlike most ponies, this never bothered Selena because with two sisters and a kingdom to rule she rarely had time to think of herself. She was far from a great mediator like Celestia and got worried easily, like she was right then.
She didn't hear the crash behind her at first, only stopping her manic pacing when she heard the thud of a chunk of the ceiling.
"Lena, we are home!" Mocked a voice.
That was not Stellaluna's voice, and only Celestia called her Lena.
"Whoops, looks like I nabbed the wrong sister," said the voice, clearly revealing in the confusion.
It was at that moment Selena turned around to face her opponent and Celestia entered and saw what used to be her baby sister.
The moon so carefully raised by Selena only minutes before she had descended into pacing shone light through the ceiling's new hole. It shed light on a monster.
Stellaluna's small frame had been altered and warped before their eyes, the blue mist surrounding the unnaturally lanky horror with a mottled black coat. The mist enveloped its creation momentarily then withdrawing and revealing what was no longer a filly but a full grown alicorn.
"Do you two dare challenge me, Nightmare?"
Selena, feeling more duty bound than ever set her horn aglow in lilac light and stepped toward Nightmare.
Celestia, throat dry and heartbroken reluctantly copied Selena as she stepped closer to her sisters.
The battle had begun, but this was a battle where nopony would win.
...
It was a blast of turquoise hued lightning that encased her graceful white form, singing her wings gray. She hurtled toward the earth below like a shooting star.
"Celestia!" screeched Selena, voice cracking with shock as she flew after the fallen princess who landed with a dull thud in the now ruined castle.
Her foe, internally gloating, was forgotten.
She found her sister's comatose form in the throne room. Selena perched over her, delirious with grief as she shed a few tears.
Then she noted the panel in the floor, knowing what Nightmare didn't.
As she trotted forward and lifted it an unwelcome thought seemed to whisper to her as the blessed contraption rose bearing five gems. Would they still work with only one sister?
Selena stared for a moment, entranced by the gems that seemed to have the power to do anything, when she was startled by a cough from behind her.
"Lena, the Elements...they are only a last resort."
"Oh, Celestia!" Selena sobbed helping Celestia stand, "Do you not see how truly desperate we are? The Elements have always been just."
Not truly hearing Selena, Celestia stumbled over to the stone contraption, her tears flowing freely. To comfort her, Selena reached over only to be pushed away as Celestia's golden aura lifted the Elements of Magic and Kindness into the air.
"Alright," she whispered, Celestia's eyes shone valiantly despite being framed with tears.
Selena nodded and instinctively selected her Elements of Loyalty and Generosity.
They both stared at the two gems left while auras of power glowed dimly around the two remaining bearers.
Hoofsteps of the one they dreaded sounded behind them. They had to do this, the only thing they could do in hopes of vanquishing the toxic Nightmare to save their sister.
"Well now, what are those little trinkets you have?"
Nightmare licked her lips. Once these two were gone and corrupted she could have eternal darkness and misery.
Celestia turned toward Nightmare; her heart was sinking. Selena tried to bury her confusion but ended up looking to her older sister for an idea of what to do.
It was then that the last two gems found what would be their temporary home. Honesty flew to Selena and Laughter to Celestia, both foreign to the faint colors surrounding the two princesses which caused them to bob nervously.
Next was a boom, followed by a blast in the form of a rainbow, and a child's twisted screams laced with a voice that was never her own.
"LUNA!" Celestia shouted, falling to her knees on the castle floor. Her Elements fell to the ground with her, every trace of powerful magic vanishing. Celestia thought this would be the last time she would ever use Stellaluna's nickname and the tears came again.
"LUNA! LUNA! LUNA!"
She stared up at the moon, now sporting an almost perfect equine silhouette of mysterious craters.
"PLEASE COME BACK!"
Selena stared down at her own Elements which had met the floor in silence. Both sets were now fossils due to the broken bond of the bearers.
Celestia kept crying as she looked out into the sky, her Luna was gone but she was unsure of what exactly had happened up there so far in the sky.
How is this just?! How is this just?! A part of her wanted to scream those words at Selena, for how could such a thing be true? Stellaluna was no tyrant, no usurper, and no criminal so why did this happen?
Why?