Rokurokubi (ろくろくび?) is a demon in the series.
Rokurokubi are a type of youkai (Japanese supernatural creatures of various origins and traits). They are perfectly human during the day, but their necks can stretch up to incredibly long lengths at night - which the rokurokubi will make use of to drain life out of passer us or just give them a good scare. Sometimes the rokurokubi is unaware of its nature as a youkai, leading to a situation where the youkai just thinks that it has a very weird dream every night, where it sees the town at impossible angles.
Devil Children Black Book/Red Book (PS)Edit
Rokurokubi can be found in Fire Land's Casino Town.