Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Y'kai (literally demon, spirit, or monster) are a class of preternatural creatures in Japanese folklore ranging from the evil oni (ogre) to the mischievous kitsune (fox) or snow woman Yuki-onna. Some possess part animal and part human features (e.g. Kappa and Tengu). Y'kai generally have a sort of spiritual or supernatural power. Y'kai that have the ability to shape-shift are called obake. Japanese folklorists and historians use y'kai as supernatural or unaccountable phenomena to their informants. In the Edo period, many artists, such as Toriyama Sekien, created a lot of y'kai inspired by folklore or their own ideas, and in the present, not a few y'kai created by them (e.g. Kameosa and Amikiri) are wrongly considered as being of legendary origin. From the 1960s on, manga artist Shigeru Mizuki popularized many types of y'kai in his works (e.g., the titular one-eyed y'kai protagonist in Ge Ge Ge no Kitaro). Lafcadio Hearn's collection of Japanese ghost stories entitled Kwaidan: Stories and Studies of Strange Things includes stories of y'rei and y'kai such as Yuki-onna.