Luna used to be haunted by dark thoughts of jealousy, but it was her sister who fell to the darkness first. She declared eternal day, before she was banished by the Elements of Harmony, leaving Luna to rule over the land of Equestria, alone.
Now, almost one thousand years later, Luna has taken another personal student under her wing, one with the potential for great things. Luna knows that she will greatly change Twilight Sparkle's life, but has no idea just how greatly Twilight will change hers.