Shirime

Shirime is a strange yōkai (literally demon, spirit, or monster) with an eye in the place of his anus. The story goes as follows: Long ago, a Samurai was walking at night down the road to Kyōto, when he heard someone calling out for him to wait. "Who's there?!" he asked nervously, only to turn around and find a man stripping off his clothes and pointing his bare buttocks at the flabbergasted traveler. A huge glittering eye then opened up where the strange man's anus should have been. This creature was so liked by the haiku poet and artist Buson that he included it in many of his yōkai paintings.

From: http://en.wikipedia.org/wiki/Shirime