In Japanese folklore, a supernatural being or strange phenomenon is broadly called a yōkai.
The category includes an enormous range of creatures and events: animal shapeshifters, household objects that become animate, frightening monsters, unusual apparitions, and uncanny occurrences. Kappa, kitsune, and many other figures are commonly classified as yōkai, although individual traditions can describe them in different ways.
The modern idea of yōkai was strongly shaped by Toriyama Sekien’s illustrated books in the eighteenth century. His catalogues drew on older legends, religious imagery, Chinese sources, and literary traditions, helping standardize recognizable forms for later readers. Contemporary manga, anime, games, and films have expanded the category’s popularity worldwide.
Yōkai is not simply another word for kami or ghost. Kami are sacred beings honored in Shinto, while yūrei specifically refers to ghosts or spirits of the dead. Boundaries can shift across historical and regional traditions, so classification depends on context.