Vertical Force is an interesting top-down vertical shoot-'em-up employing 3D to display two different play depths, which the player can move between at will. It operates much like Hudson's other shooter, Star Soldier, except that it's headache-inducing for different reasons.
Debug Menu and Sound Test
Changing 0xB330 in the US ROM (0xB340 in the Japanese ROM) from 20 to 22 will force the game to load into a debug menu which includes a level select and sound test. The sound test in particular is notably quite nice looking, featuring names for every music track and sound effect and set against a backdrop of a 3D star field which streams toward the player like in that old screensaver. This may suggest earlier plans to make it more readily available.
At 0x1DB7C in the US ROM or 0x1DB58 in the Japanese is the following string:
VSU DRIVER Version 0.19a,Copyright(c) 1994-95 Hudson Soft,Program : LU.Iwabuchi,Driver : ChaCha-TYPE,Note : Prototype
Near the end of the ROM, at 0xFFDD0, right by the internal name and gameID included in all Virtual Boy games, are build dates: