Successfully complete the indicated task to unlock the corresponding character:

Adelheid: Defeat Adelheid in Arcade mode when he challenges you.
Ex Kyo Kusanagi: Successfully complete Challenge #30
Gai: Defeat Gai in Arcade mode when he challenges you.
Geese Howard: Successfully complete Challenge #40.
Hotaru Futaba: Successfully complete Challenge #15.
Jyazu: Defeat Jyazu in Arcade mode when he challenges you.
Magaki: Successfully complete Challenge #6.
Mai Shiranui: Successfully complete Challenge #20.
Mr. Big: Successfully complete Challenge #35.
Robert Garcia: Successfully complete Challenge #10.
Shion: Defeat Shion in Arcade mode.
Sho: Defeat Sho in Arcade mode when he challenges you.
Silber: Defeat Silber in Arcade mode when he challenges you.
Tung Fu Rue: Successfully complete Challenge #25.