Fan Casting Youkai in Sort by Tropes

妖怪 (Youkai/Yokai/Yōkai, roughly "bewitching spectres") are a grand collection of various supernatural creatures and phenomena that pop up in Shinto religion, their spelling derived from the Chinese pinyin Yaoguai. They have a lot in common with The Fair Folk—some youkai are good, others are evil, and many have their own alien set of values. Some are mischievous, others avoid humans entirely. Shinto is an animist religion, and youkai are often associated with natural features such as forests and mountains. While sometimes glossed as "demons",note a closer Western equivalent is probably the ancient Roman genii, spirits or "monsters" (in the Monster Mash sense).