To unlock Leann as a fighting character in Versus and Survival Modes, Kou
must defeat her at the end of the game. You can only fight her if you
choose Kou inside of Mikado Group, then Kou or Volt when fighting the black
panther in the hallway of the Galeo.
Leann has several outfits to choose from. Her normal outfit is R1, the
white bathrobe she wears at the beginning of the game is L1, R2 gives you
her regular outfit but colored differently (white top, blue shorts), and
L2 turns her white bathrobe blue.