Enter these codes on the title screen (not the intro) that is seen after finishing story mode. If you have already finished story mode with a character before just select them and continue the story which will take you to the title screen. You can do this as many times as you wish.
|Right Left Right Left Up Down Up Down A B||Unlocks Don Kanonji|
|Right Right Right A A A L R L R||Unlocks Komamura Sajin|
|Down Down Up Down Down Up A A B B||Unlocks Kuromade Zennosuke|
|Up Right Down Left Up Right Down Left L R||Unlocks Kurotsuchi Mayuri|
|B B A A B R A L B A||Unlocks Shiba Kaien|
|A B R L A B R L Up Down||Unlocks Soi Fong|
|Left Left Left B B B R L R L||Unlocks Tousen Kaname|