Saburou is a Oni that was working with Vaenndr in Chicago to find his brother, Eiji. He lives in the sewer system of the city. He is not very smart, but can control his aggressive impulses, although barely.
Book 1: The World Awakens
He was defeated and captured by Alexander Zhao and his Band, and interrogated by them to explain more about the mythical creatures that were operating behind the curtains in the city. He stroke a deal with Alexander to release him if he were to help the Band deal with the cultists of the Red Hand. He got the deal and was free to forge his path in the local mythical community.