User with this ability either is or can transform into a youkai (ghost, phantom, strange apparition), a class of supernatural monsters in Japanese folklore. Japanese folklorists and historians use yōkai as "supernatural or unaccountable phenomena to their informants". In the Edo period, many artists, such as Toriyama Sekien, created yōkai inspired by folklore or their own ideas, and in the present several yōkai created by them are wrongly considered as being of legendary origin.