Production on the film did not begin until three years later in 1969, when the project first appeared on Toho's production lineup, still under its original title. Ogawa's script was heavily altered, removing the global scope of the original story and moving the setting entirely to the fictional South Seas island of Sergio Island. Producer Fumio Tanaka later said he believed the film went through three drafts, and stated that the original draft featured the alien invaders being attacked with nuclear weapons.
Production on the film did not commence until three years later in 1969, when the project first appeared on Toho's production schedule, still under its original title. Ogawa's script underwent significant changes, eliminating the global scope of the original narrative and relocating the setting entirely to the fictional South Seas island of Sergio Island. Producer Fumio Tanaka later stated that he believed the film underwent three drafts, and mentioned that the initial draft featured the alien invaders being attacked with nuclear weapons.