Yaone

In the anime and manga Saiyuki, Yaone serves as the alchemist for the youkai prince Kougaiji.
Background
She was the daughter of an alchemist, but was chosen by the woman-eater Hyakuganmaoh. Kougaiji saved her from this fate, and she has since sworn her life to his service. She also acts as a 'babysitter' for Kougaiji's sister, Lirin.
Weapons and Abilities
Her preferred weapons are a short spear, explosives, and various poisons. In volume two of the manga, she tries to eliminate the Sanzo Ikkou, first by poisoning their food and then by gassing them. Her primary combat rival is Hakkai, who is quite similar to her in personality, being calm and collected. Curiously, she somewhat reminds Hakkai of his deceased lover, Kanan. Additionally, both are sometimes seen fighting alongside each other, rather than against each other, and even with the rest of the Sanzo Ikkou. However, she has made it clear that she is completely devoted to Kougaiji.