Final Fantasy XIII is a tale of souls from a futuristic civilization illuminated by the Light of the Crystal. Created by a supernatural being known as the fal'Cie, it is a safe haven for the humans who live there and is protected by giant commissioned machines.
The main characters you will be able to control in the game are Lightning, Snow, Vanille, Sazh, Hope, and Fang. They are all made into l'Cie at some point and can use magic. Summons which are popular in the FF series return with the name Eidolons, and each I'Cie has one.
The Active Time Battle system from the previous games will return, with some improvements. Commands and attacks can now be stacked into battle slots, which allows for use of multiple commands in one turn for a devastating combo. These commands are filled based on the ATB cost which eliminate the need for MP. Also your entire party's health is restored before every fight since magic cannot be used outside of battle. Another new feature allows you to basically rewind a battle and let you play it again if you didn't like the outcome of the match.