Five Figure Fanwork Exchange

Like hokuton_punch says, the Saiyuki/Saiyuki Ibun characters are all canonical but unnamed priests of very high rank ("sanzos"). The Uten Sanzo is the only one of the main/current day story line sanzos not to be canonically named, and we hear about his death from the person who killed him and who wishes to kill one of the four main characters, Genjo Sanzo (who holds two sutras, and is thus the Seiten and the Maten Sanzo of his time). Saiyuki Ibun is set during the training of the previous generation of sanzo priests, and the "current" sanzos are their predecessors. We see them from the back right at the end of the sole volume of Ibun, having a brief, irreverent conversation with the temple's high priest. Nothing about their gender or appearance can be discerned other than one of them is a youkai.