Two of the Kasuga deities ride upon sacred deer to the land that would become Kasuga Taisha Shrine. These are Takemikazuchi no Mikoto, now enshrined in the first sanctuary of Kasuga’s Main Hall, who is believed to have come from Hitachi Province (present-day Ibaraki prefecture), and Futsunushi no Mikoto, who is believed to have come from Shimōsa Province (present-day Chiba prefecture) and is enshrined in the second.
 
KITAZAWA NatsukiEnglish by Mary Lewine 
Buddhist Art Paradise: Jewels of the Nara National Museum. Nara National Museum, 2021.7, p.335, no.183. 

According to the legend, the deity Takemikazuchi-no-mikoto, who is enshrined at the first sanctuary in Kasuga shrine, came from Kashima in Hitachi (today's Ibaraki prefecture) riding on a flying deer and landed on the top of Mt. Mikasa. He was then enshrined at today's sanctuary at the foot of the same mountain. The figures in this painting are the deity Takemikazuchi-no-mikoto and his attendants Nakatomi Tokikaze and Hideyuki, who became the head Shinto priests of Kasuga shrine.
It is uncommon that another figure riding on deer-back was added at the upper part of the painting. This figure is not identified, but it is conceivable that it is the deity Futsunushi-no-mikoto, who came from Katori in Shimousa (the area which covers parts of today's Chiba and Ibaraki prefectures) and was enshrined at the second sanctuary of Kasuga shrine.
A branch of a sakaki tree attached to a mirror is an indication of the original interpretation of the legend which alleges that the deities were immaterial when they moved to Kasuga and their spirits had entered into the sakaki branches which were then carried by the deers to Kasuga. Mt. Mikasa is painted at the top of the picture, which, together with other motifs in the picture, makes it a painting describing the legendary origin of Kasuga shrine. 
Masterpieces of Nara National Museum. Nara National Museum, 1993, p.70, no.53.