After you have done what is described below to unlock these characters, you can select them on the Fighter Select screen by moving the cursor to "Random" and pressing the Circle button to cycle through the ones you have available. These are only available in Quick Play modes.

Effect - Code

Hardcase - Defeat Arcade Mode (Any Difficulty)
Mask (Jeet Kune Do) - Defeat Arcade Mode on Hard Difficulty with a JKDer
Mask (Kickboxing) - Defeat Arcade Mode on Hard Difficulty with a Kickboxer
Mask (Street Boxing) - Defeat Arcade Mode on Hard Difficulty with a Street Boxer
Mask (Tae Kwon Do) - Defeat Arcade Mode on Hard Difficulty with a TKDer
Mask (Wrestling) - Defeat Arcade Mode on Hard Difficulty with a Wrestler
Reina - Complete Story Mode