He's ravaged Tokyo. He's challenged the Eighth Wonder of the World, slain a lepidopteran goddess, and driven from Earth a planet-destroying demon. What's left for the King of Monsters? How about raising a child? That's right: in his eighth feature Godzilla becomes a father. And while the results are somewhat mixed, they're arguably better than you might have expected.
The decision to make Godzilla a parent may seem like an odd one but at the time it wasn't entirely out of left-field. It was around this time that Godzilla's first (and arguably only) major competition emerged, the giant turtle kaiju known as Gamera. Although initially an antagonist in much the same manner as Godzilla, the Gamera films quickly transitioned to a more family-friendly style, presenting the eponymous turtle as the "friend to all children." The strategy seemed to be working for Daiei, Gamera's owners, so Toho producer Tomoyuki Tanaka thought it might be worth a try with Godzilla.
Veteran director Ishiro Honda was not very convinced by Tanaka's argument and decided to sit the film out, instead directing King Kong Escapes. As a replacement, Toho turned to Jun Fukuda, who'd directed the previous film Ebirah, Horror of the Deep. While not quite as successful as Honda's Invasion of Astro-Monster (selling 3.5 million tickets in comparison to Invasion's 3.8 million), Ebirah had been much cheaper to produce and Fukuda had proven himself in the eyes of Toho management. Joining him were screenwriters Shinichi Sekizawa (who also wrote Ebirah) and Kazue Shiba, who were given a simple directive: create a baby Godzilla who could serve as a link between children and the King of the Monsters.
Largely because of this shared crew, Son of Godzilla draws a number of inevitable comparisons to its immediate predecessor. Like Ebirah, the film takes place on a remote island in the South Pacific (probably a part of the Ogasawara chain), far away from the urban environments of most early Showa films. Similarly, it features a Godzilla who is sort of ambiguously good... or at least occasionally helpful, not quite the Earth-defending superhero of the 1970s yet, but clearly more philanthropic than in previous films. It does have an identity of its own though and actually (somewhat paradoxically) aims for a return to the science-themed plots of the 1950s and early 1960s, while also simultaneously making Toho's pivot towards children.
The films starts pretty abruptly. A plane traveling over the Pacific Ocean begins to have navigation problems as its controls are scrambled by some kind of radio signal emanating from the nearby Solgell Island. Just as the plane's crew realizes the signal's pattern corresponds to brain waves they catch sight of Godzilla in the distance, heading towards the transmission's source. Whoever's sending the signal, it seems they've got Godzilla's attention.
We then switch perspectives to the island itself, where a scientific team dispatched by the United Nations has been sent to test an experimental weather control system. Their work is interrupted when a (different) plane flies overhead, dropping off a man from it. The team meets the intruder at his landing site and learn he's a reporter named Goro Maki who has come to the island to uncover the nature of their research. The lead scientist, Dr. Kusumi is not particularly eager to share top secret information with the journalist but is unable to convince him to leave of his own accord and so allows him to stay as the team's cook (and general manservant). Before Maki can settle in, however, the camp is attacked by a group of human-sized praying mantises, and the team is forced to fight them off.
Afterward, Maki, while foraging, spots what he believes to be a native woman. The scientists disregard his claim, however, noting the island is uninhabited (aside from them). One scientist in particular, the surly Furukawa, storms off in a huff, agitated by Maki's presence and questions. Taking a friendlier turn, Kusumi explains the importance of their project: he and the other scientists hope to discover a way to artificially alter the humidity and temperature of a climate, so they can create new arable terrain with which to feed the world's rapidly growing population (this theme, would, incidentally, be revisited in another Godzilla film many years later). However, because a weather control device could be weaponized, they've had to keep their work a secret.
The next day, the scientists attempt to freeze the island as a test of the device's effectiveness. Maki runs off, despite the scientists' warnings, concerned for the safety of the girl he believes to have seen. Unwilling to halt their experiment, the scientists proceed and launch their device. However, the radio transmission to control the device is interrupted by an unknown signal coming from the island's center, which causes the device to go off prematurely, drastically altering the intended effects. Instead of freezing the island, the device unleashes a tropical storm and bathes the island in radiation, causing the Kamacuras to mutate and grow much, much larger. What's worse, the team's equipment devastated by the storm, leaving them isolated and barely able to sustain themselves.
The signal we learn later, is emanating from an egg, within which is incubating the so-called son of Godzilla, Minilla (a portmanteau of "mini-Godzilla"). We never actually learn for sure whether Minilla is Godzilla's offspring—it does beg the question of who Godzilla's mate was (unless he... or rather she... is asexual like the 1998 iteration)—and there's no clear indication as to the egg's origin, but it's sort of beside the point. Minilla is evidently the same species as Godzilla and is calling to him through an electromagnetic signal of some sort. To readers who've seen the the 2014 film, this may sound a bit familiar; it's possible this is where the idea for two kaiju calling to one another across global distances through electromagnetic pulses came for. Or not.
On the whole, Son of Godzilla's a bit of a mixed bag. On the one hand, the film is actually surprisingly entertaining despite being one of the most widely reviled films in the franchise. The monster fights are well-choreographed, the human plot's a decent sci-fi yarn, and the cast does a good job at hitting both its dramatic and comedic high points. The script isn't one of veteran kaiju scribe Sekizawa's best, but it's not one of his worst either and it manages to be both funny and suspenseful when it wants to be.
On the other hand, Minilla's design is pretty awful and the new Godzilla suit isn't much better either and looks even more flimsy than the one presented in Invasion of Astro-Monster and Ebirah. Oddly enough, the poor creature design doesn't carry over to the Kamacuras or the giant spider Kumonga, who each look pretty good in motion (the Kamacuras in particular are much more interesting than their simple concept suggests).
A great deal of the film's dreadful reputation hinges really on the unpopularity of its eponymous star. Whatever Toho's intentions—whether it was to capitalize on Gamera's popularity or merely put a friendlier face on the King of the Monsters—Minilla never took off in the way Tomoyuki Tanaka wanted. Widely reviled by most fans, the monster only appeared in three more films and his last appearance was more of an in-joke than anything else. Toho would later revisit the idea of a baby Godzlla in the Heisei series (with much better results) but Minilla never caught on.
I think a large part of what Toho missed was the same thing that a lot of filmmakers miss about kids. Kids don't want to be a baby monster. They don't want to be a kid superhero. They don't want to be the "boy wonder." They want to be Batman, not Robin. They want to be Obi-Wan, not kid Anakin. They want to be Godzilla, not Minilla. Fortunately, Toho does seem to have caught on: while the remaining Showa films continued Toho's pivot towards children, they dropped Minilla. Eventually, Toho realized kids wanted to be Godzilla.
Still, even if Minilla's conception was haphazard and his bizarre half-baby, half-kaiju design left a lot to be desired, Son of Godzilla isn't actually all that bad. The plot is actually pretty solid compared to a lot of kaiju films and as I stated earlier, there's an even mix of humor and drama, both of which work pretty well. Even Minilla's scenes aren't all that bad: it's actually pretty amusing to watch Godzilla's unsteady attempts at fatherhood, which range from neglectful to overly strict, depending on the situation. And the monster fights are pretty cool too.