Shirime

The Shirime or Nuppori-bōzu (Japanese: 尻目 or しりめ, meaning "butt eye") is a type of yokai that likes to scare people late at night, but is otherwise harmless in Japanese mythology.

Appearance
From a distance, shirime appears to be a normal human being. When close enough, however, it becomes apparent that it is a yokai. It has no facial features, but located in its butt hole is a large eye which shines like lightning.

Behavior
Shirime approaches travelers on the road late at night, looking like a man wearing a kimono. Once it has their attention, it asks them if they have a moment to spare. Before they can answer, the shirime drops its kimono to the ground and bends over, spreading its butt cheeks and revealing the giant, shining eye located inside of its butt hole.

Other than its very startling behavior, shirime does not do anything harmful. It appears to thrive solely on the joy of scaring people.

Origin
Although there are very few documented encounters, because of its alternate name (nuppori-bōzu) and its shocking behavior, it is very likely that shirime is a close relative of the noppera-bō, another faceless ghost. In this case, shirime's true form may simply be a shapeshifted animal playing a practical joke on humans.