When you see the TAKARA screen, press Select 3 times. You'll hear a sound. If you go to the players screen you can play with Rugal and with Saishu. If you see the TAKARA screen, keep pressing the Select button until you heard a little sound twice. Now you can play with Nakoruru too!
Press START + B buttons when you are in the screen where you choose the fight-mode and choose a fighter. Then the computer will fight against the computer.
When you are in the screen where you can select a player, press START + B. The computer will select a player. When you are not satisfied with this, press B again.
Pause the game when you are playing. When you press SELECT multiple times, the game moves slowly. Only, you can't make any moves because you are pressing the SELECT button constantly.