Unko-san: Tsuiteru Hito ni Shika Mienai Yousei Junjou Ha

Synopsis (en anglais)

On a legendary island shaped like an unusually regular turd, a population of turd-people and insanely aggressive animals go about their hilarity-packed day to day lives. Central character Yoshiko Un is known as Unko-san, but you're unlikely to meet her--the island appears only to the fortunate few, to whom they give good luck. (Source: The Anime Encyclopedia)