Due to a certain incident, Detective Yasaka Genichiro of the Public Safety Division retired from the front lines. One day, a girl named Joshua, who calls herself a "space police officer," appears before him. Initially suspicious of Joshua's behavior, Yasaka is forced to believe her after witnessing her unique discharge and detection abilities. With no place to go, Joshua temporarily stays at Yasaka's house, where she reveals her next objective: "Monster extermination." Reluctantly, Yasaka follows Joshua to the location she indicates, where they are confronted by a gigantic mechanical monster! With Joshua's arrival, Yasaka is drawn into a grand destiny. What are the cosmic monsters' objectives? And who exactly is Joshua? The ultimate monster battle action begins here!