No.6 is a dystopian science fiction anime series based on a novel by Atsuko Asano. It follows the story of Shion, a boy from the utopian city of No.6, who encounters Nezumi, a fugitive from the city's oppressive regime. Their meeting leads Shion to discover the dark secrets behind the city's facade and question the true nature of freedom and justice. The series explores themes of friendship, rebellion, and societal control.