Play as Reiji
at the title screen press A, B, Right, Left, Right, Left, Down(2), Up(2)

Play as Gouriki
at the title screen press Up(2), Down(2), Left, Right, Left, Right, B, A a

Regain 2 Health
Press C-up, C-Down, C-Left, or C-right repeatedly after you are knocked down

New bodies
After you create and train a character with over 90 moves you will unlock two new bodies that you can use

New Outfits
Hold L and press Left or Right at the character selection screen. The
character portrait will change colors to confirm correct code entry.
Then, select a character while L is still held.

Special stage
Break down all ten buildings in a single stage. Return to the stage selection screen and press Start.

Morphing Reiji
After you unlock the secret character Reiji, begin a battle with any character using Reiji. When your strength meter is about 1/3 full press the "L" and "R" buttons at the same time. If done right a wave of light will come out of him and he will begin to transform. He can transform into the characters Yami or Hikari.