From the start of the game, you only can play as Joe on Kids or Adults mode. Here are the various rewards you get for your accomplishments in the game:
Unlockables[edit]
GameCube unlockable music video.
PlayStation 2 unlockable music video.
Finish Any: Unlock "Viewtiful World" Music Video
Finish Adults: Unlock Sylvia, Unlock V-Rated Mode
Finish V-Rated: Unlock Alastor, Unlock Ultra-V Rated Mode
Finish Ultra-V Rated: Unlock Captain Blue
PS2- Finish Any: Unlock Dante
All characters have the same cutscenes as Joe's story with certain models replaced. All dialogue is dialogue from Joe's story played backwards and with various tone alterations.
Finish the game with a Rainbow V rank for every task in Adults or higher: Unlimited VFX for the character you did it with
Unlimited VFX is without a doubt the hardest thing to unlock in Viewtiful Joe. To go about unlocking it is generally referred to as the "Rainbow-V Challenge." To get a Rainbow V rank for a level, you cannot have even one task with a regular V ranking, or else you will fail. Soft resets (hold B+X+Start for the GameCube) are very useful, and patience should be kept in good supply.
To use your Unlimited VFX, start a new game. When selecting your character, hold down Z on the GameCube before selecting them. You should see "Super" over their name, and the text should billow faster. Then just go along until you get VFX; you'll find that the meter never goes down unless you do a Slow-Dodge.
PS2 Push Button Unlockables[edit]
A Push Button Code is available for both regions of Viewtiful Joe that will unlock everything from the title screen. At the title screen, input the following:
USA: 
PAL: 
A chime will let you know you've succeeded.