After extensive research on the Mutsu lullaby "The Sleeping Priestess," lyrics were discovered that appear to be even closer to the original.
The following includes thoughts on how the song came about, as well as its meaning.
"The Sleeping Priestess: Verse One"
Sleep, child, Lie in peace
Sleep, child, Lie in peace
If you cry, the boat you'll ride
The last trip to the other side
Once you get there
Sacred marks you'll bear
they shall be peeled off
Should you fail to lie still
The words "Lie in Peace" in this version of the song seem to connote death, rather than sleep.
The words "sacred marks" may be related to the area's legend of the "Tattoo Master." Perhaps in the original religious song, it expressed a meaning of "engraving a tattoo."
"The Sleeping Priestess: Verse Two"
Sleep, child, Lie in peace
Sleep, child, Lie in peace
If the priestess wakes from her dream
Perform the rite of stakes
Her limbs pinned tight
Lest the doors open wide
And suffering unleashed on all
After researching various oral traditions, there was found to remain here the vestiges of a spirit world faith of sending the spirits of the dead to the "sea" -- despite the fact that it is in the mountains. This "sea" may signify the "underworld."
If the "doors" are taken as the doors to the Other World, then "Lest the doors open wide / And suffering unleashed on all" seems to connote that if the doors to the Other World open, some disaster will occur.
This song may have originally related to a ceremony that protected the gate to the Other World.
The combination of elements such as the title "The Sleeping Priestess," the priestess "waking," sleep and laying to sleep, juxtaposed with the word "to pin," lends the meaning of the priestess being "aided to sleep." A sacrificial property can thus be read into the song.

Following is a diagram found in regional documents, combined with the legend that seems to be based on ceremony and religion. In the center of this illustration, there is a small shrine where "Engraving Shrine" is written. The part of the song about "tattoo" lends credence to the theory that the song may have been sung here.
Deep in the "Engraving Shrine" there is a vast sea (the underworld) and the shrine is drawn as the boundary between This Shore and The Other Shore. The lore accompanying the diagram is as follow[s].
Break fresh skin, Engrave the Holly
Impale the tattoo stake
Subdue for Eternity,
To sleep in the rift
Like the song lyrics, the lore can also be read as having the same human sacrifice - like aspect of "Impale, Subdue and Sleep."
Note:
- While viewing this note in the menu you may view an image of a diagram depicting the Engraving Shrine by pressing the O (circle) button.
