Dissidia 012 Final Fantasy
Prologus is a PSN exclusive downloadable title available on March 15 that precedes Dissidia 012 Final Fantasy PSP title which comes out on March 22nd. Prologus also features Aerith!
Both Prologus and Dissidia 012 let you control Lightning from Final Fantasy XIII as a fighter, and Prologus will let you transfer over any items you earn into Dissidia 012.
More interestingly, Prologus features Aerith as an assist character for attack, defense, and Assist Breaks.
Look for our review of Dissidia 012 Final Fantasy in the April issue of Game Informer and on this site soon.