Marin, a bright and cheery girl in junior high, has a caring adoptive family. Her life alters drastically when a peculiar mirage appears in the sky above the entire earth. Soon thereafter, hostile androids referred to as Monomakia descends from the sky formation known as Brigadoon and commences hunting the young Marin. While attempting to flee, she stumbles upon a blue bottle in a shrine. From this bottle emerges a protector: Melan Blue, an extraterrestrial bearing a sword and gun. Together, Marin and Melan Blue must save the planet. Amidst their perilous journey, they must contend with family conflict, school bigotry, the police, and uncover Marin's past while decoding Melan's enigmatic mission. Their trust and bond grow as they navigate through their trials. The story unfolds in 1969 Japan, chronicling a diverse group of friends and foes.