Get through the game and at the ending after the sequences, youll be able to move around and go places, but theres no enemies in the world now. Head to the place where you originally meet Reala (lens girl) At the first forest dungeon.
From there, An FMV Sequence will play and when its over youll be asked if you want to save. Save your data on another slot and then go to the loading screen and load it.
When you load youll be at a shop where you can spend all of your grade points that you earned for extra features such as Double Experience, Carrying over extra items, Stats, and other things.
Along with NewGame+ Giving you access to the Grade Shop, You can access a new hidden dungeon by collecting the 15 Unlucky Stones that now exist in the world.