The story of the Battle with Nightmare Moon is well known, but few ponies know but half the story. The other half was an unseen battle, as Luna struggled to overcome her past choices and past demons. She struggles to overcome the does within her, as well as the ones she made during banishment. But another foe has been waiting for her this whole time. After all, even in Equestria, a monster like Nightmare Moon doesn't just appear out of nowhere.