This film features a radical new re-imagining of King Ghidorah, a three-headed golden dragon widely considered to be Godzilla's arch-enemy and one of his most popular monster co-stars. King Ghidorah made his debut in Ghidorah: The Three-Headed Monster (1964) and most recently appeared (ironically in a heroic role) in Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack (2001). The character is also confirmed to appear in the upcoming Hollywood film Godzilla: King of the Monsters (2019), the sequel to Godzilla (2014).
Full nude character models were designed and published for the Hotua twins, for the intimate scenes one of them shares with the main character Haruo. This also constitutes one of the extremely rare instances in all of the Godzilla movies where a sexual relationship between characters is implied.
Following a series of Japanese interviews in late 2018 in which co-director Kôbun Shizuno admitted to not being a fan of the Godzilla franchise, a number of differing English translations and interpretations have spread within the Western Godzilla fanbase. This lead to the misconception that the director actively attacked the fans and wanted to avoid showing monster fight scenes in the films. These notions are all false. Shizuno recognized that this new interpretation of Godzilla and the anime films' storytelling might be controversial among some of the more "traditionalist" fans, but he never went after the fan base, and the decision to tone down the exaggerated monster fights came from the top brass at Toho Studios. It is true that he wanted to put a new spin on certain aspects of the franchise (like the way Godzilla fires his trademark "atomic breath", or the depiction of MechaGodzilla), however these changes were not implemented because he hated the series, but because Toho Studios wanted to be more experimental with the films to reach new audiences. One reason these misconceptions have spread is that the Japanese interviews had a jocular, tongue-in-cheek tone, and most English translations didn't pick up on this fact.
"Sufficiently advanced technology is indistinguishable from magic" is mentioned as a quote from "one of Earth's scientists." It's actually a quote from Arthur C. Clarke.
During Haruto's "dream" sequence, the WWII aircraft destroyed by Mothra is the Enola Gay, the B-29 bomber that dropped the atomic bomb on Hiroshima in August 1945.