Emperor is a classification of mechanical-type man-made shikigami.
Models
'Model G1 Emperor'
It's used in the story by Daizen Amami and Etou.
'Model G2 Emperor'
It's used in the novel by Miyo Kurahashi.
Purpose
It's used as Defensive Shikigami by powerful individuals.
The Onmyo Agency is protected by two models of the Emperor.