In the late 90s, developers often hid debugging tools and extras behind button combinations. Brigandine: The Legend of Forsena is famous among the retro community for a specific set of codes that unlock quality-of-life features and even a secret difficulty mode.

You can now select the Esgares Empire as a playable nation. Note that they do not have a dedicated story mode like the other five kingdoms, making it a "hard mode" of sorts. Essential GameShark Codes