The "companion book" is the Sexual Teachings of the Jade Dragon. See, a White Tigress has a Jade Dragon (a man who supports her, protects her and cultivates with her.) as well as multiple Green Dragons (men who are only there to fellate and draw sexual energy from). She absorbs the sexual energy through the mouth. The Jade Dragon "raises" his sexual energy by watching her with the other men and engaging in dual practices with her.