Hyakki Yagyō

Hyakki Yagyō is not a single originating myth but a long‑standing motif attested across medieval tale collections and later visual arts. The phenomenon appears in classical narratives such as Konjaku Monogatarishū and Uji Shūi Monogatari and is represented in Muromachi–Edo picture scrolls (e.g., Hyakki Yagyō Zu) and later printed yōkai encyclopedias. Over more than a thousand years the motif developed as a way to depict and catalogue many kinds of nocturnal supernatural activity rather than to record a single creation story.

As a phenomenon Hyakki Yagyō is described and depicted as a procession moving through streets at night. Visual sources vary: some handscrolls and prints show a parade of diverse yōkai in formation, while other accounts emphasize disorder or riotous movement. Participants are generically described as yōkai and other supernatural creatures (with some sources mentioning oni among them), and visual/cultural examples include animated ritual implements (a monk's fly whisk, boots, a Buddhist gong) and individuated monsters catalogued in Hyakki picture‑encyclopedias by artists such as Toriyama Sekien and Utagawa Yoshiiku.

Accounts emphasize collective, public movement and danger to humans: encountering the procession is reported to result in death or being spirited away in some tales. Variant legends attribute leadership (e.g., the yōkai Nurarihyon is named as a leader in a later legend). Sources also report that yōkai may recognize or react to human signs in specific stories (for example, a Konjaku Monogatarishū tale describing yōkai avoiding a man because of his garment marking). Ritual specialists (onmyōji) and their exorcism scrolls are consistently presented as effective countermeasures in tradition.