Oasis

Silly Lera is a mentally retarded girl who lives in a magic oasis thirty thousand years in the future. All people around her have their souls regularly purged from weird or dark desires, which allegedly, makes the oasis the best place in the world to live. The whole life in the oasis is controlled by Maxwell's daemon who lets anyone out but lets only good people in. When the daemon decides that Lera's father can't return, she embarks on a dangerous quest to challenge the daemon's decision and save her dad's life. The only problem is the daemon has never been wrong before, so no one is going to believe a silly girl.