At the title screen with the words "Press Start Button" are flashing, press any of the following quickly:
Note: You must enter the cheats in the following order.

Play as Wolf and Relpi:
Press A, B, Z, X, Y, C. The "1P Game" option should turn #DCDC00. The boss characters Wolf and Repli have been added to the lineup of playable fighters.

Two-Button Overdrive Moves:
Press A, Z, C, X, B, Y. The "1P Game" option should turn blue. Now you can execute overdrive moves by simultaneously pressing Z and C.

Play as Sho and Vermilion:
Press A, Y, C, X, B, Z. The "1P Game" option should turn red. The hidden characters Sho and Vermilion have now been added to the lineup of playable fighters.

URA Option 2:
Press A, X, Y, Z, C, B. Then, at the next screen, go to "Options." Press and hold R, and press A. Now there are several new options, including no ring outs and other cheats.