The mountainous regions of Japanese prefectures Yamanashi, Nagano, and Niigata are known for a particularly dangerous kind of itachi. In these areas, grandparents warn their grandchildren to beware of kama itachi, or "sickle weasels". These itachi have learned to ride the swirling whirlwinds of this cold region. They have claws that are as strong as steel and as sharp as razors. Their fur is spiny like a hedgehog, and they bark like a dog. They move so quickly that they are invisible to the naked eye, and they come and go with the wind.

Kama itachi travel and attack in threes, striking out at people from thin air. The first kama itachi slices at its victim’s legs, knocking him to the ground. The second one uses its fore and hind legs to slice up the prone victim with thousands of dreadful cuts. The third one then applies a magical salve which heals up the majority of the wounds instantly, so that none of them proves fatal. It is said that the Kama itachi strikes with such precision that it can carve out entire chunks of flesh from its victims without causing even a drop of blood to be spilled. The attack and the healing happen so fast that the victim cannot perceive them; from his perspective he merely trips and gets up with a bit of pain and a few scratches here and there.

One theory about the kama itachi’s origin is that it is only a joke: a play on words based on a sword fighting stance known as "kamae tachi". However, legends of invisible beasts that ride the wind and attack humans in a similar manner are found in all regions of Japan, and the sickle weasel remains a popular explanation for these incidents throughout the country.