The very good reason for this is that we have 80% of the book already written. Firstly because we wrote the entirety of a medieval-period Japanese sourcebook called Tetsubo that we originally intended for publication as a Warhammer supplement. And second because our gaming group ran a Heian Japan role-playing campaign using Paul Mason's Outlaws of the Water Margin rules, and the events of that campaign formed a large part of FL Book Six.
Although Tetsubo was not destined to see the light of day in its WFRP incarnation, putting it together was about the most fun project we've ever worked on together. Not least because it gave us an excuse to watch dozens of great Chinese and Japanese movies. At any rate, between the 200+ pages of manuscript we have for that and the half-dozen scenarios from the Kwaidan campaign, there's enough there for a pretty thick book. And that's even before we add the FL RPG rules. And you can grab a free copy of the Tetsubo part of it by clicking on the cover there in the sidebar. Or here.
In this famous Kuniyoshi triptych, Princess Takiyasha, the daughter of Taira no Masakado, uses a scroll to call up a skeleton spectre to menace Mitsukuni, Lord of Shimoda. According to legend, Takiyasha's powers of witchcraft derived from her father, who foiled attempts on his life by surrounding himself with magically created duplicates. In the center panel, we see that the Lord of Shimoda has just defended himself against an assassin, so perhaps the purpose of the spectre is not to bite off his head, as videogamers and anime enthusiasts may suppose, but simply to give him some sleepless nights in which to reflect on this disturbing intimation of mortality.
Ad Blankestijn explores a possible inspiration for Kuniyoshi's flesh-tingling apparition here on his fascinating blog. Ad writes:
"...I could not only admire ukiyo-e by Kuniyoshi such as “Mitsukuni defying the skeleton specter,” but also saw mummies of yokai. These were apparently preserved in temples, where in the past they must have been taken out of their boxes and shown to the gullible country folk whenever the priest wanted to scare them into belief in higher powers. They were made by stitching together the bones and skulls of small animals as monkeys and birds and adding feathers or skin (or doing intricate things with washi paper). These yokai mummies looked so creepy that they really scared me more than the prints!"