During the day, nukekubi look like ordinary humans, usually women. At night, their heads detach from their bodies and float around freely. While they eat the same food ordinary humans do during the day, at night their heads seek out human flesh and blood to eat. These vicious yōkai will bite humans and animals to death.

Despite being dangerous, this yōkai is actually rather easy to kill. If its body is moved while its head is roaming around, then the head will not be able to reunite with the body and will die in the morning.

Nukekubi are closely related to rokurokubi, yōkai that resemble ordinary women by day by can stretch their necks at night. Nukekubi are the more violent of the two, and tales about them started appearing more recently than those concerning rokurokubi.

FUN FACT: Nukekubi are sometimes thought to be humans with an affliction somewhat similar to somnambulism (sleepwalking).

Examples in various media:

Kubinashi (Nura: Rise of the Yokai Clan)

The Gamin-Sama, formerly known as the Hitouban family (Usher and Tora)

The creatures in Junji Ito's "The Hanging Balloons" take inspiration from the concept of nukekubi, although they are separate entities from the people they resemble. Instead of looking like ordinary heads floating around, these creatures have nooses dangling below them which they use to try and kill the person they look like. These are especially horrifying because damaging the floating head also hurts the person they resemble.