Tokiko Mima, also known as "Key," is a 17-year-old girl from the Japanese countryside who, despite her human-like appearance, is a robot. When Key's grandpa, Dr. Murao Mima, dies, he sends her a deathbed message in which he tells her that she may become a genuine girl if she can earn thirty thousand friends. As a result, Key transitions from the peaceful Mamio Valley to the bustling streets of Tokyo, where she soon encounters her childhood friend Sakura Kuriyagawa. Key immediately falls in love with idol singer Miho Utsuse and wonders if being a singer will help her to make the necessary number of friends to become human. But Miho has a sinister secret: she is linked to Jinsaku Ajou, an old foe of Dr. Mima.