Kamaitachi (鎌鼬) is a Japanese yōkai, most common in the Kōshinetsu region.
There are several conceptions of how it looked or operated, but the most common is one of a trio of weasels with sharp claws, riding on a gust of wind and cutting people's skin on the legs. According to this interpretation, the first weasel knocked the unsuspecting victim down, the second cut the victim's flesh and the third applied medication to the wounds, so that at the time the victim realised what was happening they were left only with painful wounds that weren't bleeding. Sometimes the three are described as brothers, sometimes as triplets. This account can be traced back to Toriyama Sekien, who was presumably also the first to imagine the apparition to have the form of a weasel. The weasel was a typical Toriyama pun - one of the folk names for the apparition was kamaetachi (構え太刀), meaning "attacking" which he changed slightly to mean "sickle weasel".
The idea of lightning fast weasels wielding razor-sharp claws appealed to manga and anime artists and the kamaitachi often appear in those media.