If you look at some of the screenshots for Final Fantasy XIII-2, entering a new time period or selecting it from the Historia Crux brings up the year and calendar era, AF. What does AF stand for?
Square Enix explain that "AF" stands for "After Fall" — as in, the fall of Cocoon, since Final Fantasy XIII-2 takes place after that event. As for Lightning? Lightning is in Valhalla, locked in battle against the guy below, who was also in the game’s very first trailer.