The Kamaitachi is an invisible weasel that arrives on a whirlwind and slashes people with sickle-like claws. The wounded feel almost no pain and do not bleed, leaving cuts whose cause cannot be known.
In some traditions three of them divide the work — the first knocks you down, the second cuts, the third applies a salve that blocks the pain. The dread comes from the unseen mingling with the everyday wind to wound.