Yōkai (妖怪, ghost, phantom, strange apparition) are a class of supernatural monsters in Japanese folklore. 妖怪（ようかい）は、日本で伝承される民間信仰において、人間の理解を超える奇怪で異常な現象や、あるいはそれらを起こす、不可思議な力を持つ非日常的な存在のこと。妖（あやかし）または物の怪（もののけ）、魔物（まもの）とも呼ばれる。
Bakeneko (changing cat), in Japanese folklore are shape-shifting and often mischievous cats. Although some were known to benevolent and sometime helpful, many were known to be cruel and devour their human masters. There are several ways a cat can become a bakeneko. The most common tales say that the transformation happens when a cat becomes too big, lives past the average age, or it's tail becomes too long and splits in two.
Not all bakeneko were malevolent. In fact some were quite benign saviors. One tale tells of a famous geisha who had a cat that tried attacked its owner, trying in vain to swipe at her ankles. The geisha the killed the cat, only to have the cats spirit come back. It wasn't until after the cat then killed a snake that was hidden near the woman's feet that she realized the cat was trying to save her all along.