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.
It wasn't until 1969 that production on the movie began, after the project had been listed on Toho's production list for three years. Ogawa's script was heavily revised, stripping away its global scope and moving the story to a fictional island in the South Seas called Sergio Island. Producer Fumio Tanaka later claimed that the film went through multiple drafts, with one version featuring alien invaders being attacked by nuclear bombs.