Unlock Soul Edge
Beat Arcade Mode with each character OR play the game for 20 hours. You can also unlock him by entering ALL as a name.

Unlock Seung Han Myong
Unlock Soul Edge then beat Arcade using Hwang, immediately followed by Seung Mi-na. Make sure you perform their alternate endings to guarante he is unlocked.

Unlock Siegfried! Costume
Unlock Siegfried's 8th weapon in Edge Master mode to get evil Siegfried from his bad ending.

Unlock Sophitia! Costume
Unlock Sophitia's 8th weapon in Edge Master mode to get Sophitia without armour.

Unlock Sophitia!! Costume
Unlock every characters 8th weapon in Edge Master Mode to get Sophitia in a swimsuit.

Unlock the Ultimate Weapons
Beat Soul Edge the return to the map screen. Press circle and chose to move. The CPU will select the destination of the characters final weapon each time until you win the match.

Alternative Costumes
Default Costume = Square
Default Recolour= X and Square
Alternate Costume = Triangle
Alternate Recolour = X and Triangle
New Soul Blade Costume = Circle

Change Replay View
Zoom Out = Triangle
Zoom In = Square
Top View = Up
Horizontal View = Down
Spin Right = Right
Spin Left = Left

Alternative Title Screen
Beat the game with all 10 characters.

Soul Blade Namco Voice Trick
You can alter the voice that says Namco at the start of the game:
Seung Mi-na's voice = Hold L1 + L2
Fast Voice = down
Normal Voice = left

Change Your Victory Stance
You can change your victory stance press either Triangle, Square, Circle or X after you have beat your opponent.

Alternative Endings
Enter the following commands when the black lines disappear from the top and bottom of the screen:

Siegfried: Press Triangle
Rock: Press Triangle
Hwang: Press Square
Cervantes: Press Triangle
Taki: Press X to guard against Soul Edge's attack.
Seung Mi-Na: Quickly press down, up to make her side step her fathers attack.
Li Long: Press square, triangle repeatedly to make him stand up.
Voldo: Quickly press up, down repeatedly until Soul Edge breaks.
Sophitia: Press right to make Sophitia bathe in the water.
Mitsurugi: Press left or right to avoid the bullets. Then run forward and attack Tanegashima with B before he reloads.