Rokurokubi

Rokurokubi are demons that take on the form of normal humans during the day, but after nightfall they reveal their true forms, extending their necks to great lengths. They typically disguise themselves as women, though there have been a few depictions of male rokurokubi. These creatures fall into two types: The more docile group that attempts to coexist with normal people, and the hostile individuals that prey on humans (usually unsuspecting lovers) while they are asleep. Malicious rokurokubi have the ability to completely detach their heads from their person. Because of this, a method to dispatch of these demons is to destroy their bodies while the separated head is feasting elsewhere.