BGM Option
     To  unlock  the BGM option you have beat the game. The BGM option
can only be used in-game.

Unlock Beast Class
     After  you  defeat  the  5th  floor boss go back to where you met
Kurogane  and  he  willl  give  you the Trust Band. Go to the Explorer
Guild and you will get the Beast class.

Unlock special items
     These  are  the boss items that are only acessible by defeating a
boss in certain conditions

Unlockable:     How to Unlock:

Brute wing      Kill Chimarea when its poisioned

Red claws       Kill Hellion with death status ( Issen, Climax)

Snow bone       kill Scylla under or in 5 turns

Cut Quill       Kill Harupia when she is poisioned

Red Spine       Kill Colossus without bashing it (No bash element attacks)