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Playstation - Tokimeki Battle Puzzle Egg cheats

Unlock the Sub-Boss as playable character:
Finish the story mode using each character.

Unlock the Boss as playable character:
First unlock the sub-bosse. Then go to the title screen, and push 
the following button combination:
Up, Up, Down, Down, Left, Right, Left, Right, X, Circle. 
Note: You can't play with the Boss in story mode.