From the latter part of the Heian period (794–1185), mirrors were used to represent Buddhist deities and kami. Mirrors were used in the early period of this tradition, but they were eventually replaced by metal votive plaques with incised images, and from these kakebotoke were born: hanging metal votive plaques with three-dimensional images affixed to them. This is an early example of a mirror with a deity inscribed in its surface. An image of a seated Amida (Skt. Amitābha) is incised on its face.
 
NAITO SakaeEnglish by Mary Lewine 
Buddhist Art Paradise: Jewels of the Nara National Museum. Nara National Museum, 2021.7, p.336, no.169. 

This is a round bronze mirror with a line-engraved image of Amida-nyorai (Amitābha), who is seated cross-legged on a lotus seat and is making a finger sign. The mirror is thin. An inner circle is represented on the mirror-back and a rather low round knob is in the center. A pair of cranes holding pine branches are described within this inner circle of the mirror-back, and many other pine branches are scattered both inside and outside of the circle. Several aspects of Japanese type mirrors made during the days of Regent Fujiwara are found in this mirror. The purpose of this mirror was not practical use but it was designed as an implement for Buddhist rituals, because the knob of this mirror does not contain a hole for a braid.
The image of Amida-nyoral is engraved in keribori style but the outlines are precisely drawn. This image is representative for Amida-nyorai images made during Regent Fujiwara's days and reflects the graceful and gentle taste of those days. Some remnants from the tin plating are observable on the surface of the mirror, which suggests that the surface of this mirror was originally plated with tin. 
Masterpieces of Nara National Museum. Nara National Museum, 1993, p.123, no.97.