Very little is known about Oriya. He owns Kou Kaku Rou, an elegant traditional restaurant that is secretly a brothel for the rich and powerful. He inherited this from his family, who held Kou Kaku Rou for many generations (it is described in the manga as one of the oldest, if not the oldest restaurant in Kyoto). He is a friend of Muraki's from college, and Muraki's only known friend. He wears a very distinctive and ornate kimono and is often seen smoking a traditional Japanese kiseru pipe; he practices kendo and is an expert with the katana. He has very strong, somewhat ambiguous feelings toward Muraki. In the most recent continuation of the series, he is shown to be hosting and caring for Ukyou, Muraki's childhood sweetheart.
Though he is usually seen as a neutral or sympathetic figure in the story, he is also an active collaborator of Muraki's. He has helped Muraki cover up his murders through his network of high-ranking officials, and in return, Muraki has disposed of troublesome elements among the women of his brothel.