Yiyú, also known as Black Jade, is the former tiger to call of one of the Harlequin. She is delicate, petite, and Asian with long straight, shining black hair. She can fit under Anita's arm like Anita can fit under most of her boyfriends' arms. Yiyú has been severely abused by her former master, who used pain to control her.
Yiyú comes to St. Louis during the events of Bullet to spy for her master. She pretends to be an attack survivor. Anita discovers that she is a black tiger and manages to "tame" her, but her master intervenes and tries to control both her and Anita. Anita with the help of Domino succeeds in breaking the connection between Yiyú and her master.
She remains in St. Louis with Anita, and although she can fight and is fearsomely good, the centuries of abuse have left her with the mentality of a victim.
She makes Anita "heteroflexible" rather than heterosexual.