百怪図巻（ひゃっかいずかん）
Hyakkai Zukan
A 1737 scroll of thirty yokai by Sawaki Sūshi, the model Sekien worked from.
Forty years before Sekien’s first book, the painter Sawaki Sūshi finished a scroll of about thirty monsters, each named, each standing alone against the paper. The yamabiko as a small dog-like creature, the otoroshi crouched with its hair hanging over its face, the nure-onna with a woman’s head on a serpent, the ushi-oni, the nuppeppō: Sekien took their shapes almost line for line into Gazu Hyakki Yagyō, and so the shapes passed to everyone after.
The Hyakkai Zukan is one of a family of similar scrolls, the bakemono-zukushi, that circulated among Edo painters; copies and variants survive in several collections. It is the clearest evidence that a standard set of yokai images existed before 1776, and that Sekien gave it a wider public rather than inventing it.
Related yokai
Yamabiko
山彦（やまびこ）
The echo in a Japanese valley was heard as an answer before anyone drew the thing answering — and when painters finally gave it a body, they produced a small animal that is neither quite a dog nor quite a monkey.
Otoroshi
おとろし
Otoroshi appears in a 1737 scroll and in Sekien's 1776 book as a hunched, hairy creature — on top of a torii in Sekien's version. Neither says what it does. The story about it dropping on the impious was read out of the picture later.
Nure-onna
濡女（ぬれおんな）
In Iwami in 1933, a fisherman walking home at night was handed an infant by a wet-haired woman — and when he threw the bundle down and ran, something else came out of the dark after him.
Ushi-oni
牛鬼（うしおに）
Toriyama Sekien's 1776 print shows a bull-like head on a squat clawed body at the water's edge — and tells us nothing else about it.