This film was released in the U.S. as Destroy All Planets, which may have been a ploy to make people think it was Destroy All Monsters, perhaps the greatest of all Toho monster battles.
This time, Gamera is defending our planet from aliens. He starts off by destroying one of their ships, but not before an entire planet declares that he is their enemy.
The aliens come back to Earth and learn Gamera’s one weakness: he loves children. They kidnap some kids and force him to do their bidding, but before long, he’s broken loose and is battling all of the aliens at once, who have combined their form into the menace known as Viras.
Daiei was in financial trouble, so this movie suffers from a smaller budget than previous films. But this is where the idea of Gamera protecting kids from aliens and monsters began. Yet it’s also the first of the series to use flashbacks from past films to pad the running time. This will get much, much worse as Gamera would battle on.
There was also an agreement with AIP that an American kid had to be in the movie. They couldn’t find any kids that could speak Japanese, so the studio cast Carl Craig, whose father was an army soldier stationed in Japan, despite Carl having no acting experience.