This week, continuing the theme of Supernatural Storytelling, we’re discussing the Hiyakki Yakô.
Prompted by curiosity, he arose; and when he got to the main building he found Hiyakki Yakô (meaning a procession of one hundred ghosts)—a term, I believe, which had been generally applied to a company of ghosts. The ghosts fought, wrestled, danced, and made merry. Though greatly alarmed at first, our priest became interested. After a few moments, however, more awful spirit-like ghosts came on the scene. The priest ran back to the small room, into which he barred himself; and he spent the rest of the night saying masses for the souls of the dead.
At daybreak, though the weather continued wet, the priest departed. He told the villagers what he had seen and they spread the news so widely that within three or four days the temple was known as the worst-haunted temple in the neighbourhood. —
Ancient Tales and Folk-lore of Japan, by Richard Gordon Smith, 
If you’re familiar with anime and manga, there’s a good chance you’ll recognize the scene described above before.
There’s a scene in the manga for XXXHolic that has Watanuki participating a Hiyakki Yakô under a full moon. The grand procession at the “reveal” of Spirited Away – shortly after her parents turn into pigs, Chihiro witnesses a grand procession of all manner of spirits and Yokai that are consistently linked back to other well-known sorts of Japanese spirits.
Shows with a Feudal Fantasy bent, like Inuyasha, will sometimes have mad streams of restless, angry, or hungry spirits, terrifying as they writhe against the sky.
There is a level of curiosity and helplessness when standing in the presence of the Hiyakki Yakô . The concept varies from medium to medium. The actions of the spirits range from a apparent lack of disinterest in the human (typically only one) observing the spirits, to malignance if the human were to be noticed – but that they are going towards something more important, more interesting (or maybe just more tasty).
(What are your favorite examples of the Hiyakki Yakô? Add any examples that you know of to the comments! Is there a piece of folklore or Japanese Culture you’d like us to cover? Leave us a note!)