Biwa-bokuboku (琵琶牧々), sometimes only referenced as Biwa (琵琶), is a biwa yōkai.
Biwa-bokuboku's head is is an actual biwa, being a tsukumogami of said instrument. His eyes, which have purple sclerae and gold irises with black pupils, are placed by the side of the strings which are connected from the top of his head to his teeth. He has bony light purple arms and legs and wears what appears to be long wavy beige straws.
He appears in episode #57 of the fifth anime adaptation, The Legendary Yōkai Nue!!
In the live-action film series, Biwa-Bokuboku increases his face from one to four when someone plays him.