Enter the password BABABABA, then press L and R on the second controller. Then the code should turn into "100% CHARACTERS" in Japanese. Now, go to the main character and final boss, you will see a big difference at their outlook and their power level.
Enter the password BABYBABY to unlock all characters.
Play as the Super Final Character
To play as the super final character, the one with the shades and monster-looking body, follow these instructions: Select VS BATTLE MODE and enter the password "BABABABA". Now press and hold L and R on Player 2. (The password box will change to "100% within 100%"). Start the game and the final character will automatically become the monster-looking freak.
View Ending and Credits
Select STORY MODE then enter the password "BABYBABY".