Proof of an onryo found in a credible historic record is the example of Fujiwara no Hirotsugu written in Gembo's Sotsuden of Shoku Nihongi (the second of the six classical Japanese history texts), but scholars are divided over whether there had been onryo earlier than that.
史料的に確実な例としてあげられるのは、『続日本紀』の玄ボウの卒伝にみえる藤原広継の怨霊であるが、それ以前については意見がわかれている。