Final Fantasy XIV: A Realm Reborn
Square Enix is crossing over two Final Fantasy titles. Lightning from Final Fantasy XIII and the upcoming Lightning Returns: Final Fantasy XIII will be in MMO Final Fantasy XIV: A Realm Reborn, and elements of the MMO will be in Lightning Returns.
Players can fight alongside her in one of the MMO's Full Active Time Events, which are periodic battles. If you complete this event, you'll get equipment (including weapons) that are based on those in Lightning Returns.
Conversely, if you play Lightning Returns, you can acquire a Miqo'te costume (see gallery below) by tracking down clues. Also, Lightning Returns players can obtain weapons and shields themed after the city states of A Realm Reborn by completing side quests in Lightning Returns.
Final Fantasy XIV: A Realm Reborn is available now for PC and PlayStation 3, and will release for the PlayStation 4 sometime in 2014. Lightning Returns: Final Fantasy XIII (click for the game's TGS trailer) comes out for the Playstation 3 and Xbox 360 on February 11.