Wikipedia
Ōkagami is a Japanese historical tale written in around 1119 by an unknown author. It covers the period 850 to 1025, the golden days of the Fujiwara family's rule. It is said to be a successor (世継物語, yotsugi monogatari) with the records of the Eiga Monogatari.
In the tale, the writer listens to a conversation mainly led by a 190-year-old man, Ōyake no Yotsugi (大宅世継, literally "world-successor"), who recalls the past. A 180-year-old man, Natsuyama no Shigeki (夏山繁樹), adds comments and a young samurai puts questions to these two elders. This narrative strategy makes the story vivid and allows for the natural addition of various opinions and criticisms.
The structure is modelled after traditional Chinese history books like the Records of the Grand Historian. It consists of Preface, Stories of Emperors, Stories of Ministers, Miscellaneous Stories and Post-fin.
This and three other tales with mirror (鏡 kagami, also read kyō) in their titles are collectively called four mirrors (四鏡 shikyō).