Successfully complete story mode to unlock more characters each time it is finished.
Bonus FMV sequence
Complete story mode with Sion.
Hidden FMV Sequence
Successfully complete story mode with Sion.
Increased character rank
You can increase the rank of extra characters in survival and versus modes every time story mode is completed (all except Volt, Sion, and Kou)
Unlock Leann Cadwell
To unlock the character, complete the game, using ONLY Kou. You fight her before the credits. She's easy to beat if you know her moves. Try and 'juggle her' with a reapted circular uppercut, and the smash her with a drop kick.
Unlock Sion with black hood costume
Complete survival mode by defeating the black-hooded version of Sion to unlock that costume in survival and versus modes.
Unlock Topless Duragon
Complete the game three times using any character. After defeating Duragon for the second time, he will get up again and fight topless. Defeat him to unlock Topless Duragon in versus mode. Unlock Kou with MSF costume Play through story mode with any character. When you come to it, use Kou to infiltrate the Mikado Building. The MSF costume for Kou will now be unlocked in survival and versus modes.
Unlock Wong Leung
To unlock Sion's sensei, Wong you must play through the game as any character. When you come up to the battle against Kaldea (the battle right before the final fight), have any character other than Sion fight her. Then, use Sion to complete the game. During the end sequence, right before Dominique comes to visit Sion while he is working the door of the bar, you will view a flashback sequence where Sion will do battle with his master, Wong.
Wong fights similar to both Sion and Dauragon. He uses the same two-fisted attack as Dauragon (where he can hit an opponent both in front of him, and behind him), as well as leg sweeps similar to Sion. You can use normal attacks against him, but one special move in particular works very well.
Block attacks from Wong, and while he is recovering from one press the ES+MEDUIM buttons (whatever you have them assigned to) to perform the Torpedo Kick move, which will take off a bit of damage and knock Wong off his feet. Turn that into a pattern: Block, Torpedo Kick, Block, Torpedo Kick, etc. to defeat Wong, who you can then use in the Versus mode.