Chameleon — India Millar

Keiko's revenge on her enemies is almost complete. Like her namesake, the chameleon, she has changed herself to attract and entrap the men she seeks. Now, just one man remains unpunished. But before she can complete her vengeance, karma destroys her plans cruelly. Niko -- her adopted younger sister -- has been kidnapped. Keiko is sure she knows who is behind the abduction, but she cannot act alone to get Niko back. She is forced to turn to the most unlikely ally to help her -- Akira, the most feared yakuza in Edo.
Karma forces Keiko to change her colors to get what she wants. She has become as adaptable as the chameleon. But first and last, she is still a warrior woman of the samurai.