Square Enix is being very tight-lipped about its "Fabula Nova Crystallis" series that encapsulates Final Fantasy XIII, Final Fantasy Agito XIII, and Final Fantasy Versus XIII. All three games take place in the same universe but at different time periods with different characters. A new trailer for Agito and Versus shows off some action that looks a bit like Kingdom Hearts in some places:
Agito's story features a nation that went on an invading spree against its neighbors until it encounters a lone kingdom guarded by a crystal; the crystal suddenly shatters and a group of students appears to make a stand against the invaders. Even less is known about Versus but the protagonist is the final heir of an isolated nation that guards the last crystal on the planet. Notice a possible link between Agito and Versus?
More details about Agito and Versus are to be revealed at the January 11, 2011 conference mentioned at the end of the trailer.