Three games and a spot on Dissidia’s roster just aren’t enough for Lightning. Final Fantasy XIV: A Realm Reborn has a Full Active Time Event where you fight alongside the Final Fantasy XIII protagonist. When you complete this event you can earn armor and weapons modeled after Lightning Returns: Final Fantasy XIII. It looks like female characters get a Lightning costume while male characters can earn a Snow costume.
Lightning Returns: Final Fantasy XIII also has crossover items from Final Fantasy XIV: A Realm Reborn. A Miqo’te costume is hidden in the game and players can find clues on how to unlock it hidden in Lightning Returns. Lightning can also find a sword and shield themed after the Final Fantasy XIV: A Realm Reborn states Limsa Lominsa, Ul’dah, and Gridania by completing side quests.