Iya Yotsugi (弥世継)
Iya Yotsugi is a history book covering the reigns of two Emperors, Emperor Takakura and Emperor Antoku, and is said to have been written by FUJIWARA no Takanobu in the early Kamakura period, although it is no longer extant.
"Mizu Kagami" (The Water Mirror), "Okagami" (The Great Mirror), "Ima Kagami" (The Mirror of the Present), and "Masu Kagami" (The Clear Mirror) (in order of appearance) are now called 'Shikyo' (the four historical narratives of the late Heian and early Kamakura periods with the word "mirror" in the title), and of these, there is a blank period of time between "Ima Kagami" and "Masu Kagami," which accords with the reigns of both Emperor Takakura and Emperor Antoku.
It is "Iya Yotsugi" that is equivalent to the historical narrative called 'Kagamimono' which concerned the reigns of the both Emperors. (Yotsugi is another name of "Okagami," and "Ima Kagami" also has a different name of "Shoku Yotsugi.")
Also, Jyakucho, who is considered the author of "Ima Kagami," was Takanobu's real father.
In the opening pages of "Masu Kagami," which is almost certain to have been written in the first half of the period of (Japanese) Northern and Southern Courts (around the middle of the 14th century), the author made a definite statement that "Masu Kagami" was a sequel to "Iya Yotsugi," which naturally suggests that "Iya Yotsugi" had already existed in that time. Also, there is a possibility that Yoshitoshi TADA, a scholar of Kokugaku (National Learning) in the first half of the Edo period, read Iya Yotsugi because he mentioned in a list of educational books for women called 'Jugo Goso' (Ten Narratives and Five Storybooks) along with 'Shikyo,' "The Pillow Book" and "Essays in Idleness."
However, this book is not extant today becoming 'the illusory historical tale' because it covered only short period of time and there were many narratives which dealt with the same period as "Heike Monogatari" (The Tale of the Heike), in addition to the influence of the disturbances of wars.