In the film, Gamera and authorities must deal with the sudden appearance of a carnivorous winged creature awakened by volcanic eruptions.
Gyaos was created as a response to Toho's Frankenstein Conquers the World and The War of the Gargantuas, with Yuasa pitching to writer Niisan Takahashi his idea to turn Dracula into a kaiju.
Gamera vs. Gyaos was theatrically released in Japan on March 15, 1967, on a double bill with Chiisai Tôbôsha.
An eruption at Mount Fuji attracts the giant turtle kaiju Gamera, whose arrival is witnessed by a young boy named Eiichi.
A research team of geologists is sent to investigate the phenomenon in Shizuoka Prefecture, but are killed by a supersonic ray emitted from a cave which slices their helicopter in two.
The Chuo Expressway Corporation's plans for a roadway face challenges when the local villagers refuse to leave.
A plan is formed to disorient Gyaos with a rotating platform for long enough for the sun to rise and kill it, using artificial blood as bait.
Gyaos is lured out but the plan fails when the power station supplying electricity to the platform overheats and explodes.
The headmaster regales a plan to Shiro, inspired by Eiichi, to start a forest fire to kill Gyaos.
[9] The film's production cost was ¥60 million ($167,000), however, this figure does not include studio overhead, cast and crew salaries under contract, nor print and advertisement.
[12] A real office in Akasaka, Tokyo was used for the road construction board meeting after Yuasa asked the son of the company's president (working for Daiei at the time) to arrange the location.
[16] The ending theme Gamera's Song was composed and arranged by Akira Komachi, lyrics by Hidemasa Nagata, and performed by the Hibari Children's Choir.
This resulted in appointing foreign cast members and enhanced child-friendly direction for subsequent Gamera films.
[24] Yuasa held a meeting to discuss how to jump into the action scenes as quickly as possible to retain children's attention.
[25] The film's opening was inspired by real volcanic eruptions from the Philippines, Indonesia, and Kamchatka that were happening at the time of production, with fears that Mount Fuji would become active.
[27] Producer and senior managing director Hidemasa Nagata wanted to include the protest because he found societal issues made films more interesting.
[33] Yuasa made Eiichi point out Gyaos' nocturnal nature, feeling that it was a detail only a child would notice.
"[35] The car split scene was added after Takahashi saw the Toyota Corolla deluxe at a motor show, as a result, the vehicle was not produced for the film.
[43] Yuasa recalled spending time, energy, and money on the shot of the miniature volcano exploding, however, he later felt the result was not worth it.
[44] Yuasa disliked the oatmeal formula used to simulate flowing lava in other films and instead backlit translucent molds and had them pulled by hidden cables.
[45] Yuasa felt that nighttime matching shots were more easier to achieve than daytime opticals due to film elements not requiring precision.
[47] For the scene with Okabe being lifted by Gyaos, the camera was tilted at a 90 degree angle while the background shifted horizontally.
[50] Gamera's blood was pumped manually by the crew, which Yuasa found difficult to match the animation to Gyaos' beam.
Perhaps it is because the man inside the suit swooping on wires or carefully crunching models of Nagoya is a born actor.
[67] Film historian and critic Stuart Galbraith IV wrote in DVD Talk that the film "strikes a pretty fair balance between epic scenes of destruction and the material more emphatically geared to children," with its "dark but outrageously unrealistic humor further support[ing] Yuasa-Takahashi's child-like perspective.
Factory included the Mystery Science Theater 3000 episode featuring the Sandy Frank version of the film on the MST3K vs. Gamera DVD collection.