J_menz is actually a song demon. When the demon developed a taste for human flesh, it was contained within the Shrine of Amana, but the line of priestesses (Milfanitos) who looked after the shrine and appeased the creature have died off.
However, after the priestesses tasked with maintaining the seal died or became hollow, the demon was able to escape its prison. Its name comes from its ability to mimic the song of the shrine maidens, in order to lure prey into its lair.
So naturally we're wary of listening to any of his recording, nonetheless the advice he provides is invaluable. Thus when He demands a sacrifice one of you will have to go forth.
By the way here is a sketch of his true form:
