Two youkai based on their heads. The Rokurokubi and Nukekubi posed as human beings by day. But when night falls, they reveal their unnatural features. The Rokurokubi are often tricksters, stretching their neck to frighten and spy on humans; it's sometimes involuntary. The Nukekubi, however, detach their head from their neck in order to search for human prey. The only way to defeat them is to hide their bodies until sunrise. The Nukekubi are often mistaken for the Rokurokubi.
Yes, I know Sekibanki is a Rokurokubi; so bite me.