Cate Whitlen is Ree's futuristic vampire hunter. She has hair colour not found in nature, several technological implants, and reflective retinas. You could say she has an interest in body modification.
She is skinny, left-handed, of average-to-tall height for a woman, and pale in the manner of many vampire hunter. Her hair is kept short and has been dyed purple, blue, and zebra-striped at different times. Her grey eyes reflect light like a cat's, seeming to glow in low light. There is a power jack installed in the base of her skull; it's usually covered by the collar of the beloved trenchcoat.
Cate has an internal battery that should recharge itself with every movement she makes. It was intended power her various body upgrades, giving her enhanced strength and stamina, as well as the ability to use her silvered fingernails as a taser without adversely affecting herself.
In practice, this does not happen. Cate had an electrode array sunk into her brain that, when stimulated with electricity, makes her feel absolutely wonderful - until the power stops. She overuses her battery to fuel to this high. She even carries extra wires at all times, so she can steal current for her electrode.