Once upon a time, in the magical land of Equestria, there were two regal sisters who ruled together, and created harmony for all the land.
Unfortunately, such a peace could not last forever. A feud arose between the two rulers and the kingdom was divided by more than just boundaries built in soil and on paper.
When Luna became jealous of her sister's glory in the eyes of ponies, she saw what it might lead to, coming to her sister for help. But, when scorned and pushed aside, Luna's jealousy became anger. In a fit of rage, she spirited herself and all of those under her rule, those that would follow, to her domain: The Moon.
A thousand years is a long time, though, to be holding a grudge. And now the means to mend an immortal's bond to her sibling rest in the hooves of one of Luna's subjects: Twilight Sparkle, who must descend from Luna's moon unto Solar Equestria to right a thousand-year-old wrong.
Rating subject to change pending future content.