A deadly alien force approaches Earth. Gamera intervenes and destroys the alien vessel; but before the ship is destroyed, the aliens broadcast a warning to their world stating that Gamera is their enemy.
Later on Earth a Boy Scout troop is visiting an aquarium to the scientists working on a small two-man submarine. Masao and Jim, two of the scouts, manage to talk their way aboard the sub. While in the water they spot Gamera who engages in a little race with the boys. However, their hijinks come to an end when the second alien vessel envelops the both of them in a super-catch ray.
Gamera helps the boys to escape but it remains trapped in the force field while the aliens scan his memory-waves. They learn of Gamera's one weakness, his soft spot for children. Soon after, the field weakens and Gamera is free. The aliens capture Jim and Masao, threatening to kill the boys. Powerless, Gamera lands. Attaching a brainwave control device to Gamera's head, the aliens force the turtle kaiju to do their bidding.
While aboard the spaceship, the boys continually try to escape.
- Kôjirô Hongô as Nobuhiko Shimada
- Tôru Takatsuka as Masao Nakaya
- Carl Crane as Jim Morgan
- Michiko Yaegaki as Mariko Nakaya
- Mari Atsumi as Junko Aoki
- Junko Yashiro as Masako Shibata
- Kôji Fujiyama as the Commander of Jietat
- Genzô Wakayama as the boss's voice
Gamera vs. Viras was filmed at Daiei-Tokyo Studios. The film is the fourth in the Gamera film series.
Gamera vs. Viras was released in Japan on 20 March 1968. The film was never released theatrically in the United States. It was released directly to television by American International Television in 1969 as Destroy All Planets.
In a retrospective review, AllMovie stated that the film offers "everything one expects from a massive zero-budget monster battle film" while also having "unintentionally brilliant quirky moments like the hypnotized army, Japanese men with glowing eyeballs, and a fiendishly fake-looking squid alien who wishes to attack Earth for its supply of nitrogen."