Because of the dramatic rise in sea levels, humanity has lost a significant portion of its habitable land, forcing it to depend on existing technology for survival. Among the many people impacted by this tragedy is Natsuki Ikaruga, a brilliant recent graduate who lost a leg in a submarine accident and now endures a miserable existence on a nearly deserted island. After Natsuki meets a mysterious woman named Catherine, he discovers an advanced humanoid robot that belonged to his grandmother, Nonko, a renowned climatologist. Atri, the salvaged robot who appears and acts like a young girl, tells Natsuki that Nonko assigned her an important mission, but she has forgotten what it was. Although Natsuki initially planned to sell Atri, the chance to connect with his grandmother's research through her makes him reconsider. Natsuki once had to sacrifice his dream to join a prestigious scientific mission. But as he opens up to his fellow islanders, he realizes he can still make a difference in a desolate world.