Biwa-bokuboku

The Biwa‑bokuboku belongs to the tsukumogami tradition: man‑made household artifacts that, by folklore, may become animate after long existence or when they reach an advanced age (sources commonly cite the motif of objects becoming alive after roughly 100 years). The Biwa‑bokuboku specifically is a biwa that acquires awareness and anthropomorphic form through long use, long neglect, or the passage of time as described in tsukumogami accounts.

Described in the sources as an anthropomorphic being with the head of a traditional biwa and often pictured wearing precious kimono. Accounts specifically note it 'sits calmly in a tatami room, singing and plinking,' and it is compared to similar instrument yōkai such as the koto‑furunushi. Sources do not specify exact size beyond its depiction within household rooms.

Sources describe the Biwa‑bokuboku as coming to life at night and singing and plinking its instrument‑head while lamenting neglect by a former owner. It is characterized as ambivalent rather than uniformly hostile: its actions center on noisy complaint and socializing. Alternative accounts note that Biwa‑bokuboku may meet other tsukumogami, hold noisy parties, dance through houses, or leave home to seek others with whom to commiserate. There are no sources in the provided material that attribute overtly harmful supernatural powers or standardized possession rituals to it.