Edo-period monster of the day: the kamikiri or "hair-cutter". Representative nishiki-e by Utagawa Yoshifuji (歌川芳藤) of a kamikiri in action (note the gandō). Index link to the relevant part of the University of Tokyo's collection. Transcription of text in image (with cute bonus graphic). Translation:

'There are no bumpkins or monsters [in Edo]', goes the saying, but this does not rule out tales of the uncanny (奇怪珍説). On Uzuki 20th, a maid in service at a Banchō mansion, having risen from her sleep in the middle of the night, was accosted on her way to the bathroom by something she knew not what-- a pitch-black thing which struck her head, upon which she lost consciousness and remembered no more. The commotion brought others to her aid shortly, but once she regained her senses, she discovered that her topknot had been removed and was lying two or three ken away. The black thing, she said, had been like a cat except all of velvet. This is a relation of the events as they appear in reliable sources (是は正しき書に出たるを爰にあらはすもの也).

Of course, even back in Edo days, people were capable of critical thinking. The Mimibukuro (耳袋), for example, explains that "in many cases, women cut their own hair due to some love affair or quarrel with their parents, and blame it on a monster." (Of course, it then claims that "some cases, on the other hand, really are the work of kitsune and tanuki." Thanks, voice of reason.)

Certain other possibilities should not be ruled out either. Edo was an overcrowded, urbanized society which revolved around courtesans, actors, and other groups with a financial interest in keeping everyone all het up. For women, hair was an erotic symbol, best displayed bound into a meaningful architecture accented with expensive, dangling trinketry. For leaders in the hair race, pre-fab wigs were far from rare. And you know what those wigs were made of? Another woman's hair.

With all this in mind, it doesn't seem unlikely that some kamikiri were just black-clad men driven by avarice, psychopathology, or both. In any case, the titillating possibility of such a thing was surely the key to the concept's popularity. I don't think any recorded human society has ever tired of stories about respectable women attacked and denuded by stand-ins for the male id.

The "bumpkins or monsters" saying, by the way, is most commonly seen in the form "Between Hakone and here, there are no bumpkins/boors (野暮) or monsters (化物)." It's a boast about Edo's size and cultural presence: bumpkins and monsters live in the countryside and wilderness, but from here out to Hakone, it's urban, man.