Wikipedia
Mizukagami
is a Japanese rekishi monogatari. It is believed to have been written in the early Kamakura period around 1195. It is widely credited to Nakayama Tadachika but the actual writer is unknown. It is the third book of the four mirror series.
It deals with the oldest time-period, starting with the legendary Emperor Jimmu and ending with Emperor Ninmyō. It is told by a fictitious old woman who is visited by a bhikkhu while staying at Hase-dera. All the facts are taken from ca. 1150 AD by Kōen, the teacher of Hōnen.
In its modern framework Mizukagami refers to the reflective pool in Japanese gardens, in which can be seen such things as bridges and sakura (cherry blossoms) in its reflection.