biwa-bokuboku; yōkai with a biwa head
A yōkai from Japanese mythology that resembles a Buddhist priest with a biwa (lute) for a head. The name is onomatopoeic, mimicking the sound of a biwa.
See also: 琵琶
The biwa-bokuboku is one of the yōkai depicted in Toriyama Sekien's illustrated books.
If you hear the sound of a biwa in the middle of the night, it might be the work of a biwa-bokuboku.