Yōkai (妖怪, ghost, phantom, strange apparition) are a class of supernatural monsters and spirits in Japanese folklore. The word 'yōkai' is made up of the kanji for "bewitching; attractive; calamity" and "spectre; apparition; mystery; suspicious." Yōkai are also referred to as ayakashi (あやかし), mononoke (物の怪) or mamono (魔物). The characteristics of yōkairange diversely from malevolent and mischievous entities believed to cause misfortune and harm, to those who are considered to bring good fortune to those who encounter them.

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