The mystery character that will appear in Ultra Street Fighter IV is female.
During the Capcom Cup which is a fighting game tournament, Yoshinori Ono revealed a small clue to the final new character that will appear in Ultra Street Fighter IV. He ruled out that the character is R. Mika or Hagar. He only mentioned the character is female.
Many people think the final Ultra Street Fighter IV character could be Karin. What we do know is that the character is from the Capcom universe so it’s not an entirely new character that will be appearing in the game.