The term "shikyo" refers to the four historical stories (history books with a narrative style) generically known as 'kagami-mono' (mirror works), which includes "O-kagami" (the Great Mirror), "Ima-kagami" (the Mirror of the Present), "Mizu-kagami" (the Water Mirror), and "Masu-kagami" (the Clear Mirror), that appeared between the late Heian period and the early Muromachi period. Settings for books are based on times their appearances.
Each book includes the word "kagami" (mirror) in their titles, and they are written in the form of a conversation between two elders or between an elder and the author reminiscing about days of the old. This is due to the fact that the style of Okagami, the oldest among four, was continued by the latter three.
However, "Masukagami" cites another 'kagami-mono' book called "Iya-yotsugi" ("yotsugi" is another name for "Okagami"), and it is believed that this book covers the history between that of "Imakagami" and that of "Masukagami." Since this book no longer exists, there is no way to confirm its contents.
There is also a book called "Azuma-kagami" (the Mirror of the East), although it is not included in the 'shikyo.'
The order of appearance is as follows: O-kagami, Ima-kagami, Mizu-kagami, and Masu-kagami. The phrase 'daikon mizumashi' (which literally means "Japanese radish and watering") is sometimes used as a mnemonic to help remember this order of appearance ("dai" (a different pronunciation of 大 in 大鏡) from O-kagami, "kon" (a different pronunciation of 今 in 今鏡) from Ima-kagami, "mizu" from Mizu-kagami, and "mashi" (a different pronunciation of 増 in 増鏡) from Masu-kagami). The order of the historical period appearing in each of the books, however, is as follows: Mizu-kagami, O-kagami, Ima-kagami, and Masu-kagami.