Nothing whatsoever has been shown of the battle system of Final Fantasy Versus XIII. Though, it has been mentioned that the team who designed the Kingdom Hearts battle system will be working on it. If that worries you, or if it doesnt it wouldnt suit the game anyway, it has been stated that it wont just be a recycled Kingdom Hearts battle system, its just the same dev team. The battle system is said to be very action orientated and to resemble the fight scenes of the movie Final Fantasy VII: Advent Children. (Who's team is also doing the graphics) The second there is a gameplay screenshot, it will be here.
Known Details
The battle system will feature the ability to teleport short distances. The player will be able to throw a weapon to hit an enemy and teleport to it quickly.
A resent interview with Nomura has revealed some more details about the Final Fantasy Versus XIII battle system. So far, he says, its still resembles the Kingdom Hearts battle system. However, this only applies when a sword is drawn. When the character draws a Gun, it changes to a Dirge of Cerberus: Final Fantasy VII type aiming/shooting system. Also, there is said to have something different to past Final Fantasy -- Blood! Apparently, blood will spray out when you attack the enemies. (Like in the Jump Festa Trailer) The game will also contain a freeroam airship, unlike Final Fantasy X but more like Final Fantasy VII or VIII.
This new system is certainly interesting and we'll cover it as soon as we get some screenshots and videos!