Hard Difficulty will have better drop rates and specific items

[Andromeda]

Square Enix talked more about Lightning Returns in advance of TGS with the focus on the difficulty settings for the game. They said that the hard difficulty will have improved drop rates and quality over the standard difficulty. They also said that there will be items that can't be found in the standard difficult available as well. So collector's wanting to have everything will want to play multiple times.

The reports have some variance, but it seems that killing the same monster, "thinning the herd" will cause a stronger version of that monster will appear with unique drops and different attacks. Another report stated this as the player can hunt monsters to extinction and the last monster of the species will end up being more powerful than the others. More clarification will be need to determine which is accurate.

Source: Lightning Returns: Final Fantasy XIII Will Have A Hard Mode With Better Drops - Siliconera

[Sang Hee]

Sounds pretty good. Reminds me how in FF8 when monsters leveled up they gained different spells/drops which I found useful (especially because they still weren't immune against death junction status attack ).