Maria Tsukamoto, a reporter for the Japan Flash editorial department, is actually an alien peace envoy sent from space to protect Earth—known as Mermaid A. One day, she learns that Dr. Kisaragi, a renowned geologist, has discovered ruins of an ancient civilization at Mount Sanno and immediately heads to the site. Upon arrival, Maria finds the doctor under attack and being abducted by a group of mysterious men. In the ensuing confrontation, she fights off the assailants and rescues the doctor, but sustains injuries during the struggle. That night, the doctor reveals a shocking truth—the ruins belong to the Goya civilization, an ancient race that once ruled Earth and drove humanity underground. Now, they are preparing to return and exact revenge. Armed with this knowledge, Maria faces an imminent new crisis.