Rokurokubi (轆轤首) are a species of youkai who live in hiding among humans. While mostly human in appearance they can stretch their neck to great lengths, and may be able to turn their face demonic and frightening. Rokurokubi are usually former humans, and some are unaware of their true nature (using their powers only while asleep).
Rokurokubi are often confused with Nukekubi, a similar youkai with the power to completely detach their heads.
Rokurokubi in Touhou
The confusion between Rokurokubi and Nukekubi appears to have blurred the distinction between the two races, as Sekibanki displays the abilities of both youkai (while also being referred to as a dullahan).