Menreiki is one of Japanese specters that is introduced in "Hyakki Tsurezure Bukuro" (One hundred bags in idleness) which is a collection of specters illustrations by Sekien TORIYAMA, and it is a specter of Gigaku-men Mask (masks for Gigaku, an ancient masked drama).
It says in the explanatory note as follows.
'In the era of Prince Shotoku, Kawakatsu HADA made many masks.'
As if in a dream, I think it may have been Kawakatsu's contrivance that made the masks have life.'
According to the book on noh theory, "Fushikaden" (The Flowering Spirit) by Zeami, Kawakatsu SO who was the originator of sarugaku (form of theatre popular in Japan during the 11th to 14th centuries) who served Prince Shotoku was given a mask that the prince himself had made, and Menreiki is said to have been depicted based on this anecdote.
It is a Tsukumo-gami (gods to a variety of things) that have come to life when an prominent mask became old, and there is a theory that it pleads the owner to handle with care.