Final Fantasy Type-0

Summer costumes can be unlocked as early as starting a new game. But before doing so, you must have a saved file of the demo version of the game in the memory stick being used as with the full release of the game. The saved file however must have contain the data for the costumes as were gathered from within the demo. There's a total of 14 costumes overall.

Darkness of Suzaku - Maximum Gil Exploits