These are passwords that you recieve after beating the game. You can start a new game using the password as your name.
FIREBALL- The first time you beat the game you will recieve this password. Use it as your name to start a new game as a MAGICIAN, instead of a VAMPIREKILLER, with all the DSS cards available at the start.
GRADIUS- Once you beat the game as a MAGICIAN, you'll get this password. Use it become a FIGHTER with increased strength.
CROSSBOW- If you beat the game with GRADIUS as your name, you'll recieve the password CROSSBOW. It will make you a SHOOTER with lower stats, but an incresed number of hearts and sub-weapons will be more powerful. You'll also be able to pick up a new sub-weapon, the homing dagger, a dagger that homes in on enemies.
DAGGER- If you beat the game a fourth time, this time as a SHOOTER, you'll get this password, which you can enter to become a THIEF. As a THIEF you'll have very low stats. Your luck attribute on the other hand will be huge!
Codes thanks to GameFAQS.