My first idea for this contest was an outfit based on Etro, one of the goddesses from Final Fantasy XIII mythology. I did this black dress with feathers based on one official artwork of a mural showing Etro spilling her blood, which was used to create humans in Fabula Nova Crystallis' mythology, hence the feather getting a red tint at the end. It also seems to be common to relate Etro to wings or feathers so I gave Lightning a new gunblade designed after this concept.
Etro is also the Goddess of Death, so I wanted to add a bit of black and white to it, two colors usually associated to death by many cultures.
I also wanted to make some reference to Lightning's original design for the first Final Fantasy XIII game and her current main outfit for Lightning Returns, hence her coat.