In Japanese folklore, the demon whose neck stretches at night is the rokurokubi.
Rokurokubi are a type of Japanese yōkai that look human by day but develop an unnaturally elongated neck while sleeping. Stories became especially popular during Japan’s Edo period, when kaidan ghost tales and illustrated yōkai works flourished. The name may connect to rokuro, meaning a potter’s wheel, well pulley, or another device associated with extension.
A common mix-up is the nukekubi. In some traditions, the two names overlap, but a rokurokubi traditionally stretches its neck while the nukekubi’s head detaches and flies independently. Older Chinese tales about floating heads may have influenced later Japanese versions.
Folklore sometimes treats the condition as a supernatural transformation, a karmic affliction, or even an illness. Edo-period stories also linked rokurokubi with women, servants, and performers in popular ghost stories and theatrical displays.