This is how it works: Gamera gets out of his rocket and makes his way back to Earth. A giant opal from New Guinea is brought back to Japan. There was an egg inside the opal that gave birth to Barugon, a new monster that is very strong. In order news source to attack the city of Osaka, the creature sends out destructive rainbow rays from his back, as well as a freezing spray that can incapacitate Gamera.
Decker Shado's Review: Gamera vs Barugon: The second week of Gamera Marathon features a review of the film starring the Kaiju monsters, who are (in)famous for their rainbow ray of doom! Gamera versus Barugon is a monster movie that is balanced a little differently than your typical monster movie, but is this for the better or for the worse? Fortunately, there is only one way to find out...
Source - Riffs and Reviews