Mania and Unknown mode
     After  beating the game, load your clear game data. On your clear
game  file,  you  will have Mania difficulty mode, a harder difficulty
than hard, unlocked. After you beat the game using that file, you will
unlock an even harder difficulty, Unknown.

Unlockable:              How to Unlock:
Mania difficulty         Beat the game once.
Unknown difficulty       Beat the game using a "clear game" file.