The Night Shall Last Forever

They had failed. Nightmare Moon had succeeded in her conquest of Equestria, no matter what Twilight and her new friends did Nightmare Moon was always one step ahead of them, she had destroyed the elements of harmony, the tree of harmony, there was no other power source left to defeat her and because the spark in Twilight was never realized, she and her would-be friends drifted apart and the power to defeat Nightmare Moon was never released.

Soon after that, Celestia was banished to the moon and Equestria became a land of eternal night, several ponies including those who embodied the elements of harmony were now in Nightmare Moons employ following her self appointed rise to being the one and only ruling princess of Equestria, all of them except one. Magic was the most powerful and elusive element of harmony, Nightmare Moon couldn't afford to take any chances and allow herself to be dethroned, especially by a pony so determined as Twilight Sparkle, so Twilight was locked away deep in the caves beneath the Everfree Forest with minimal food and water supplies to ensure her survival and prolonged torment with chains designed to negate the wearers attempts of using magic just for good measure.

However, Nightmare Moon knew she could not rule forever, despite not aging eventually the tire and stress of being Princess would wear her out and could potentially lead to some sort of coup, especially if the same thing that had allowed her to free herself from the moon also happened to Celestia. There was only one thing for it, she needed an heir, but who could be worthy of such a gift as to take part in producing the next ruler of Equestria? Who could ensure that her bloodline would continue and maintain her perfect world? Who could it be that would give half of their genetic make-up to the future ruler and ensure that they would be powerful enough so that even upon Celestia's return they would continue to reign supreme over a land of eternal night?

The search began.