Tsuki no Sango

Fuente: AniList

The story takes place in approximately the year 3000, when humankind arrived at the peak of its civilization, but is losing its will to keep living. It follows a girl, called "princess" by those around her, who lives on a small island with a fifty-person colony and a shining coral reef. She is a descendant of the Moon people, and the story focuses on how her ancestors supposedly came to Earth.