Rokurokubi

Some tellings distinguish a separate but closely related type, the nukekubi, whose head detaches from the neck entirely and flies off on its own to hunt at night, rejoining the body before dawn; accounts vary on whether these are two names for one being or genuinely distinct yokai, and Edo-period storytellers and artists, including Toriyama Sekien in his yokai compendia, treated both forms as part of the same broader category.

In many stories the condition is explained as a curse or karmic consequence, sometimes tied to a broken religious precept in a past life, and it is frequently discovered only by accident, as when a husband or houseguest wakes in the night to find the sleeper's neck stretched impossibly long or the head altogether missing from the pillow.

A rokurokubi is usually said to be unaware of its own nature by day, living an apparently normal life and only transforming while asleep, which allows the affliction to go undetected by the person themselves and often by their family as well.

The rokurokubi appears widely in Edo-period literature, kabuki, and woodblock art as one of the standard stock figures of the yokai repertoire, often played for both horror and dark comedy, as in tales where a servant or traveler unknowingly takes lodging with a rokurokubi and discovers the truth only through a startling nighttime encounter.

while asleep, their neck stretches to extraordinary length, letting the head wander through a house or garden independent of the body.

the nukekubi, whose head detaches from the neck entirely and flies off on its own to hunt at night, rejoining the body before dawn