Item description:

This is a simple internal backup save file in which Thunder Force IV has been cleared on a single credit (no continues used). Accomplishing this allows the player to swap out the Rynex fighter for Thunder Force III's Styx via a secret code. This code has no effect without first clearing the game on a single credit.

To use the Styx, highlight Thunder Force IV on the game select screen, then hold X + Y + Start until gameplay in the first stage begins.