Cheat code screen:
Press Left + Y when the Soul Fighter logo appears on the screen. Then go to options
and exit it. The next screen to appear will be the cheat code screen.

High energy:
Enter ABXXYA as a code at the cheat code screen. 

All weapons:
Enter XAAYBB as a code at the cheat code screen. 

Level 2:
Enter AABXYA as a code at the cheat code screen. 

Level 3:
Enter XAYAAB as a code at the cheat code screen. 

Level 4:
Enter YYBAXA as a code at the cheat code screen. 

Level 5:
Enter BABXXY as a code at the cheat code screen. 

Level 6:
Enter XAXBYY as a code at the cheat code screen. 

Level 7:
Enter ABXBYB as a code at the cheat code screen. 

Level 8:
Enter YBBAXY as a code at the cheat code screen. 

Level 9:
Enter BYAAXB as a code at the cheat code screen. 

Level 10:
Enter XABBAX as a code at the cheat code screen. 

Level 11:
Enter YBYXAB as a code at the cheat code screen. 

Level 12:
Enter XBAXBY as a code at the cheat code screen. 

View credits:
Enter AAAAAA as a code at the cheat code screen.