Everypony has something that makes them special, a gift, it's what sets them apart from each other. For Midnight, it's a gift that he never wanted, and one he sees as a curse when it takes over. With the fragments of a broken mind teetering the edge daily, it forces him to be driven away by most others in his travels, and left alone with only his 'gift' to keep him company. However, one can only stay alone for so long.
A decision to go back in to an empire he isn't welcome at, does more than just make him feel like he belongs, but gives him a mare willing to help the stallion. That so many others before her, have turned their back on.
(while this follows the events of "A Sparkle In The Guard's Eye", they can be read independently of one another, though it may answer a thing or two if you have read it. Alt Universe simply because it doesn't follow the storyline of the show.)