Years ago, we had the princesses. They controlled the sun and the moon. They brought light, hope and happiness. Then some ponies thought that nobility was oppressive and that they princesses needed to go. A war broke out and after a few years the rebels actually won. The princesses were tried and sentenced to death. Little did they know that when the princesses lives ended, so did the stars that they controlled. Immediately after their deaths, the lights went out and the world was cast into darkness. Plants died and society broke down.
Years, later, a mare on the run stumbles upon the ruins of Ponyville. Inside a house that she is hiding in, she finds a journal. It was written by the mare who used to live there, named Bon Bon. It tells the story of her life before the darkness came and her attempts to save her wife and daughter from the madness that would soon follow.