Godzilla vs. Redmoon would have been a collaboration between Toho Studios and Tsuburaya Productions. The production staff, under the direction of Kazuo Sakawa at Tsuburaya Productions, would have reportedly provided the suits for the new monsters, while Toho would have loaned the MusukoGoji suit from Son of Godzilla for the film. When plans for the film fell through, its script was heavily altered and repackaged into the film Daigoro vs. Goliath, which was also a collaborative film, produced by Tsuburaya and distributed by Toho.
A strange new kaiju emerges from the moon's surface and quickly flies down to Earth. Upon reaching its destination, the creature is sighted and dubbed Redmoon. Almost simultaneously, another kaiju appears on the nearby Habu Island, located in the Okinawa chain. This new monster is then dubbed Erabus.
The Japanese Self Defense Force comes to the conclusion that the two monsters should be led to one another in the hopes that they will kill each other. The plan to lead the two to one another is a success; however, instead of fighting, the two monsters mate, and it's revealed that Erabus and Redmoon are a female and male, respectively, of the same species. Erabus then gives birth to Hafun.
With the situation only getting worse, the JSDF is scrambling to create a new strategy to deal with the kaiju. Things go from bad to worse when Hafun is kidnapped by an entrepreneur. Shortly after getting kidnapped, Hafun dies during the moving process. With their child dead, Redmoon and Erabus go berserk and start rampaging the once peaceful Okinawa. Having sensed the two from the beginning, Godzilla finally arrives and battles with the two kaiju, emerging victorious and bringing peace back to Okinawa.
- Other than the screenplay, very else is known about Godzilla vs. Redmoon, including the design of the three new monsters. For years, it was thought that Erabus and Redmoon would simply reuse the suits for Daigoro's Mother and Goliath from Daigoro vs. Goliath. However, this is inaccurate, as Godzilla vs. Redmoon was considered prior to the production of Daigoro vs. Goliath, and eventually evolved into the latter film. Currently, the best known sources for the monsters' appearances comes from artwork drawn by Hurricane Ryu Hariken several years after the film was scrapped.
- The main idea of the film, where two different-looking monsters (who are male and female of a sexually dimorphic species) appear separately and meet each other to mate, appears to have been re-used for the 2014 MonsterVerse film with the M.U.T.O..