The Godzilla franchise, thanks to its sheer size, longevity, and different continuities, has gendered many fanon speculations over the years.
General
- It's fairly common for fans elaborating on Dr. Daisuke Serizawa's past to have made him a Shell-Shocked Veteran who served in World War 2, and this is both how he lost his eye but also what motivated him to experiment with micro-oxygen that led to the Oxygen Destroyer. The first film does imply Dr. Serizawa was affected by the war and his his age would have lined up with possibly having served or having been drafted in some role.
- Building off this, given potentially benign uses for micro-oxygen brought up in the Heisei saga, and Serizawa's horror at discovering the Oxygen Destroyer's full power; it's common to write the medical uses were the intended pursuit with the destructive use being an unforeseen side effect.
- Fan projects often create a genealogy for the various Godzillas. It's pretty common to make subsequent Godzilla the son of the 1954 individual. This is Word of Saint Paul canon for the Kiryu Saga, but many fans extend this to the 1955 Godzilla and 1984 Godzilla from the Showa and Heisei series respectively. There are also some fan projects where the Godzilla in the story is, in fact, the 1954 individual.
- Fan projects that merge aspects of the Toho continuities with the Legendary Pictures' canon frequently make Dr. Daisuke Serizawa from 1954 Related in the Adaptation to Dr. Ishiro Serizawa from the 2010s, often as an uncle or great-uncle given Daisuke's lack of children.
- Anguirus is often characterized as quite heroic despite originating as a secondary antagonist. This is due to his canonical status as the Showa Godzilla's closest companion and compendium books noting his species is capable of being a Gentle Giant. This characterization is also likely influenced by him being an ankylosaur.
- Also, fan works tend to portray Anguirus as the oldest Kaiju in the Godzilla universe, and it's not uncommon to portray him and Godzilla as being Vitriolic Best Buds with a grudging respect for each other, reflecting their long history together. This has some loose basis in Canon: Anguirus was the first Kaiju that Godzilla ever faced (back in Godzilla Raids Again, the second movie in the series), he was said to be a mutated dinosaur from an extinct species, and he and Godzilla did team up on a few occasions in the Shōwa series. Still, nothing in the series ever indicated that he was actually physically older than any of the other monsters, and his relationship with Godzilla never seemed to be especially close.
- The kaiju are very rarely given a gender in official sources, with Japanese pronouns used typically being fairly gender neutral. Fan projects frequently do characterize them with such. Biollante is one of the few frequently considered female, on account of having genes from Erika Shirigami.
- In recent years, it’s been becoming more and more popular to characterize more kaiju as female in order to have a more gender-balanced cast and avert The Smurfette Principle or Two Girls to a Team. The kaiju most commonly hit with this are:
- The version of Godzilla from Godzilla vs. Megaguirus (referred to by fans as Mire!Goji), especially after Godziban used her very distinctive design for the Godzilla Siblings’ mother.
- Manda. Became Ascended Fanon in the comic book Godzilla: Rulers of Earth (albeit only for that specific incarnation).
- Varan.
- Destroyah, especially after the fanfic The Bridge characterized her as such, and the author gave a very well-thought-out explanation behind the decision, involving actual crustacean biology and the “biology” of Dessy as seen in the films.
- Titanosaurus.
- Mothra Leo (Due to the dubs and subs never seeming to agree on his/her gender, the fact that Mothra is otherwise Always Female, and the fact that Japanese pronouns are complicated). Also another one popularized by The Bridge. However, interpreting Mothra Leo as a transgender male is also popular.
- Hedorah, though they/them pronouns are also popular, given Hedorah likely would not have a biological sex nor mental gender as humans define it.
- Kumonga.
- In recent years, it’s been becoming more and more popular to characterize more kaiju as female in order to have a more gender-balanced cast and avert The Smurfette Principle or Two Girls to a Team. The kaiju most commonly hit with this are:
- The notion that all three of Ghidorah's heads have separate personalities, with the middle head being the leader, has gained some popularity, though it tends to be avoided in more serious works as it would just complicate things. Became Ascended Fanon in Godzilla: King of the Monsters (2019), where this is said to be the case for that version of Ghidorah - which itself resulted in a new bit of fanon being created that the left head ("Kevin") is a distractible goofball who is just along for the ride.
Showa Continuity
- The popularity of the Steve Martin character from Godzilla — King of the Monsters! leads to fans often creating something of a Canon Welding between it and the original Gojira film. Having the events of the first Godzilla rampage and all of its dread happen in 1954, but with Martin having been present for the events. Becomes Ascended Fanon in Marc Cerasini's novel series, which acknowledges Martin as having been in Tokyo in 1954, writing a book (This is Tokyo) about the events; Godzilla — King of the Monsters! was an in-universe docudrama with Raymond Burr starring as the reporter.
- It's a common fan theory that Minilla is the heroic Godzilla seen in Vs. Hedorah onward. While this does have a complicated case of Continuity Snarl with Destroy All Monsters happening in 1999, the personality of the later Showa age Godzilla does match up to the human-friendly Minilla. It was notable enough that this theory even showed up in a compendium book.
Heisei Continuity
- The lack of aliens in this canon often lead to fans having the extinction-event causing asteroid heading to Earth in Godzilla vs. Mothra to be the real, alien King Ghidorah in a travel form that resembles an asteroid similar to Ghidorah the Three-Headed Monster. The explanation for the previous Heisei Ghidorah is that Futurian monster was a duplicate.
- In the novelization of Godzilla Vs. King Ghidorah (and an earlier script), the latter detail is actually true — the Dorats were cloned from the corpse of another King Ghidorah discovered on Venus.
- Fanon very frequently makes the Rebirth of Mothra series a sequel to the Heisei saga, with Mothra Leo's mother being the very same Mothra who fought Godzilla years earlier.
- Likewise, when the Shobijin in Godzilla continuities are given individual names, Moll and Lora from the Rebirth series are used. Belvera is likewise often imported in, sometimes characterized as Battra's priestess in counterpart to her sisters' tie to Mothra.
- Because the Futurians remarked that Godzilla never destroyed Japan and the series ends with the docile Godzilla Junior taking on the mantle, post-Heisei saga fan projects often have Junior remain a benign and heroic version.
- In fan works and non-Canon Expanded Universe stories, it's fairly common to portray Biollante as an example of Gaia's Vengeance with an empathic connection to the Hive Mind of the Earth itself. In the actual films, this was never the case; Biollante was just a single mutated plant with individual sentience, thanks to being cross-bred with the DNA of a human girl. Per a 2016 interview with author Marc Cerasini, the unreleased novel Godzilla and the Lost Continent would have actually had this as the case in that continuity.
Millenium Era
- Monster X is a Diabolus ex Nihilo in Godzilla: Final Wars, but fan projects frequently give them a backstory as some flavor of Bioweapon Beast created using Ghidorah’s DNA. Was Once a Man is also a common side dish for this origin, doubtless due to the influence of fanfics The Bridge and Abraxas (Hrodvitnon).
MonsterVerse Continuity
- There's a lot surrounding Mothra, being the film's Breakout Character and the Titan with the least explanation or screentime out of Godzilla: King of the Monsters (2019)'s four mains:
- To fit with this continuity's slightly more "grounded" tone, the Shobijin get adapted into a pair of decidedly human twins, Drs. Ilene and Ling Chen. While their presence is mainly a Mythology Gag, there are hints as to their connection to Mothra, mostly little ones that a casual watcher would miss. However, how deep the connection runs and whether or not the Chens are aware of it is left up to the fans, with ideas ranging from full-blown conscious telepathy to subliminal empathy. Given the novelization and the scrapped post-credits scene implying that the Chens are aware of the connection between them and the moth-Titan to some degree, most fans choose some variation of the former.
- Contrary to what many fans believe, it was never confirmed or stated anywhere that Mothra's abdominal stinger is venomous, much less that the venom is a hallucinogen and/or paralytic. However, there's nothing that says it isn't, either, and it's a logical conclusion given that there is no such thing as a "dry" stinger in Real Life animals.
- Given this film pulls a Doing In the Wizard and downgrades Mothra's divinity to Maybe Magic, Maybe Mundane, many fans prefer to choose the "magic" option and restore her status as a Physical Goddess (Or at the very least make very obvious hints about it).
- It was never confirmed anywhere that Adam/"Dagon", the fossilized Titanus Gojira skeleton found in the Philippine coal mine in Godzilla (2014) was a blood relation of Godzilla. However, most fans assumed that the skeleton belonged to Godzilla's father.
- In more recent years, a rival interpretation has emerged: that Dagon was Godzilla's mate.
