Sega Master System / Mark III / Game Gear
Finish the game once. Then, at any moment during the game, press to show the Sound Test menu.
This can also be accomplished by editing the save at 00FF,01FF,02FF,03FF and setting each to 0x80.
See the main page for Madoh Monogatari III - Kyuukyoku Joou-sama (魔導物語ＩＩＩ － 究極女王様)