Shirime

Shirime(尻目, lit. "buttocks eye") is a strange yōkai 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.