Who is Y.T. - the Kourier from Snow Crash and what is their importance?

Y.T. is a fifteen-year-old girl who has a job as a Kourier for RadiKS. Y.T. lives with her mother in a burbclave, and her mother does not know the extent of her job with RadiKS. Y.T. changes her clothes each morning and night at a local McDonald's to keep her mother in the dark. Y.T. is considered a thrasher, a hip teenage skateboarder who listens to thrash metal bands like Vitaly Chernobyl and the Meltdowns. Y.T. is an expert skateboarder and harpooner, and her upper body strength is above average due to using the harpoon in traffic. Through her Kourier training, she has learned how to get out of many difficult situations, including being handcuffed.