8 EYES

Here are codes for the three endings:

First ending  : ONAPPMBPPF
Second ending : CKBPPAAPEE
Third ending  : GBCPHAAHAD

Passwords for two secret level. When you complete the 
game once, you get this password.

TAXANTAXAN

which enables you to play again at a much harder setting.
After that there's an even harder setting that you reach
with the password

FINALSTAGE