Set a little while after Nightmare moon was defeated, and Princess Luna was brought back

With Nightmare moon defeated, and peace brought back to Equestria once again, Princess Luna is refusing to raise the moon at night. Feeling scared that with having nothing changed from before, history will just wind up repeating itself. Luna is terrified of turning back into the Monster she was, and at the same time questions her role as 'Princess of the night', and what she really means to the ponies of the land. Only this time Celestia chooses to take notice, and lend a caring hoof to her younger sister, which she realizes is something she should have done a long time ago.