Fast weapon recharge
At the title screen, press X, B, Y, A, X, B, Y, A, X, B, Y, A, X, B, Y to have your weapons charge very fast.

Bonus characters
Successfully complete the game on the easy difficulty setting to unlock a guy with a spread rocket as a special weapon. Successfully complete the game on the normal difficulty setting to unlock a girl with a hyper laser.

Easy Mode:
At the title screen, press X, B, Y, A, X, B, Y, A, X, B, Y, A, X, B, Y, A.

Unlock Spread Rocket:
Beat the game on Easy difficulty.

Unlock Hyper Laser:
Beat the game on Normal difficulty.