In New Game + just hold L1 while entering a battle.

After you beat the game once,hold L2 while entering battle.

Finish the game to make any New Game playthroughs harder. The current difficult level is represented by crystals on the main screen. Every game clear adds one crystal, and 10 crystals will become a big one. The max is 5 big crystals (difficulty increased 50 times).

Save the game at the last save point to unlock the Seraphic Gate on the world map. This secret dungeon has new characters, items and powerful enemies to be found. Once you beat it you can enter it again and the enemies will have gotten even stronger!