If you defeat a boss with a special move (L+Square or L+Triangle), an alternative portrait of them will appear.
Gallery Page
Finish Arcade Mode with a character to unlock his/her Gallery Page completely.
More Continues (maximum of 9)
Finish Story Mode three times.
Second Special Move
Reach Level 10 with a character to unlock their second special move (L+triangle).
Unlock Ryu Gentoku
Finish Gentoku's arcade mode.
Unlock Ryu Hakufu
Finish Hakufu's arcade mode.
Unlock Saji Genpou
Clear Arcade Mode with any character.
Unlockable Outfits
Finish Arcade Mode with any character to unlock three alternative clothes for that character. To select them, press L or R at the selection screen on Arcade Mode.