1000 years ago, two demigod sisters ruled over the land with harmony. They pretended to be perfect and have no problems, even though the youngest, Luna, was getting increasingly jealous of her elder sister, and the eldest was spending all her time trying to become a full goddess, stopping only to raise the sun.
Then one day, she found a spell that would turn her into a goddess, but it needed a sacrifice to work. She went after her sister who was forced to banish her to her beloved sun, accidentally alleviating herself to godhood in the process and becoming Nightmare Moon.
Since then she watched over the land, just in case her sister comes back, looking for a new sacrifice...
But that will never happen... Right?