Gamera vs. Barugon (1966)

Less than a year after Z-Plan successfully launched Gamera into outer space aboard a rocket ship bound for Mars, a meteor strikes the rocket, freeing Gamera. Hungry for more energy, Gamera returns to Earth and lands at Kurobe Dam in Japan. Gamera destroys the facility around the dam, consuming the hydroelectric power and fire, then retracts back into his shell and flies into the dam, causing it to split open and flood the surrounding area. Sensing the eruption of a volcano south of the equator, Gamera flies away to feed on the molten lava. Meanwhile in Osaka, Ichiro Hirata organizes an expedition to New Guinea, where he had served in the Japanese military during World War II and discovered a huge opal in a cave. Hirata hid the opal under a pile of rocks in the cave before he was captured and placed in a POW camp, and believes it is still hidden there. Because Ichiro walks with a limp now and is unfit to travel, he sends his brother Keisuke and his former comrades Onodera and Kawajiri to New Guinea in his place, aboard the Awaji Maru. Kawajiri poses as one of the ship's captains, while Keisuke and Onodera work as janitors. After weeks at sea, the ship approaches New Guinea, and Keisuke brings the three of them to shore aboard a helicopter. They arrive in a small village, where they are greeted by Dr. Sato, a Japanese physician who has taken up residence in the village to help treat local diseases. Dr. Sato's assistant, the young native woman Karen, warns the three men not to venture into the Valley of Rainbows, as an ancient obelisk standing in the middle of the village tells of great danger there. Onodera believes the villagers are telling them not to go there because they are hiding even more treasure there, so he leads Keisuke and Kawajiri into the jungle, bound for the Valley of Rainbows. As they approach the cave, Onodera wanders into quicksand and nearly sinks, but is rescued by Keisuke and Kawajiri. Finally, the three reach the cave where Ichiro hid the opal, and set up camp near the entrance before beginning their search. Onodera spots a highly venomous scorpion that Ichiro warned them about crawling on the wall, then shoots it with his pistol. He tells the others to keep a lookout for other scorpions, then the three of them search the cave. Kawajiri finds the pile of rocks, and wrapped in a cloth underneath it he uncovers the opal. Kawajiri excitedly exclaims that they will all be rich, but Onodera spots a scorpion crawling up Kawajiri's leg. Rather than warn Kawajiri, Onodera says nothing until the scorpion finally stings Kawajiri, causing him to fall to the ground in agony. Keisuke tries to treat Kawajiri's wound and prevent the venom from spreading, while Onodera grabs a first-aid kit. By the time Onodera arrives with the kit, the venom has already taken hold and killed Kawajiri. Keisuke breaks down and sobs over the body of his friend, but Onodera tells him to get over it and that they must leave with the opal now. Keisuke says he will hand Onodera the opal if he gives him his gun, and Onodera agrees. As Onodera walks to the exit of the cave with the opal, he decides to ensure he won't have to share the treasure with Keisuke and lobs a hand grenade in his direction. The grenade explodes and buries Keisuke underneath rubble, while Onodera escapes back to the Awaji Maru with the opal.

When Keisuke comes to, he finds himself in a clinic in the village, being treated by a local nurse. Karen enters the clinic and confronts him about stealing the opal. When she learns that Onodera has taken the opal back to Japan, Karen becomes distressed and speaks to Dr. Sato. Sato tells Keisuke that the object Onodera took from the cave is no mere opal, and the villagers believe it will bring great disaster. Karen insists on traveling to Japan to warn the people, and says that Keisuke can act as her guide. Keisuke agrees, and the two depart for Japan. In the meantime, Onodera is traveling back to Japan aboard the Awaji Maru. As the ship prepares to dock in Kobe, Onodera leaves the opal inside his jacket pocket underneath the infrared lamp he uses to treat a foot fungus he contracted from the jungle. The opal begins to glow under the heat of the lamp, then cracks open. A small lizard-like creature breaks free from the opal, then almost instantaneously grows to gigantic size, causing the ship to break apart. Onodera gets to shore safely and meets with Ichiro and a Chinese buyer for the opal. Onodera lies and tells Ichiro that Kawajiri and Keisuke died by falling from a cliff, but says they can still save the opal by hiring a diver to dredge it from the sea floor. Suddenly, a huge reptilian monster emerges from the sea and comes ashore in Kobe, smashing all structures in its path. Onodera and Ichiro flee to Ichiro's apartment in Osaka to discuss plans to salvage the opal. During the conversation, Onodera lets it slip that he killed two men to retrieve the opal, leading Ichiro to the realization that Onodera murdered both Kawajiri and Keisuke. Ichiro attacks Onodera, but Onodera overpowers and nearly kills Ichiro. Ichiro's wife Sadae tries to break up the fight, but Onodera punches her and knocks her unconscious. He then topples a bookshelf onto Ichiro, trapping him. When he overhears that the lizard creature is approaching Osaka, Onodera flees, leaving Ichiro and his wife helpless as the monster destroys the apartment and kills them.

Keisuke and Karen land at an airport in Japan and see the monster's rampage on television. Karen recognizes the creature as Barugon, a terrifying creature that menaced her people thousands of years ago and hatched from the opal. She realizes they are too late, and she and Keisuke track down Onodera. Keisuke confronts Onodera in a bar and attacks him, and with some help from Karen is able to subdue Onodera and tie him to a pole. Keisuke and Karen leave Onodera behind and contact the JSDF to decide countermeasures against Barugon. The JSDF assaults Barugon with tanks and missile launchers, but the beast wipes them out using chilling vapor emitted from his extendable tongue and a rainbow-colored death ray fired from his back. As Barugon approaches Osaka Castle, Gamera is attracted by the creature's rainbow beam and flies overhead. Gamera lands and roars at Barugon, challenging the creature to battle. The two monsters fight, with Gamera using his superior strength and fire breath to attack Barugon. However, Barugon extends his tongue and sprays chilling liquid at Gamera, freezing him solid almost instantly. Barugon approaches the frozen Gamera and begins poking him with his horn, but Gamera manages to move his arm enough to deliver a powerful blow beneath Barugon's eye, tearing through his flesh and causing him to bleed profusely. Barugon knocks Gamera onto his back and uses the chilling liquid again to completely freeze Gamera. Victorious, Barugon leaves the area and continues rampaging through Japan. Karen and Keisuke tell the JSDF that Barugon has one critical weakness: prolonged contact with water eats away at Barugon's flesh. In the past, Karen's people sank large diamonds into the ocean, luring Barugon to his death beneath the waves. She presents them with a huge 5000 carat diamond and tells them to use it to lure Barugon into Lake Biwa and kill him. The diamond is suspended from a helicopter in front of Barugon, but he does not seem to notice it and doesn't follow. With the plan a failure, the JSDF uses artificial rain to keep Barugon immobile while it works on another plan. Once Karen learns that Barugon's egg was incubated by an infrared light, she proposes that he may not be as sensitive to shiny objects as the Barugons that menaced her village in the past, and that the diamond's brilliance must be magnified to be effective. Using an experimental infrared device, the JSDF is able to successfully magnify the diamond's brilliance, then places it on a truck to lure Barugon. Barugon notices the diamond and follows the truck to the lake, where it is placed on a boat. When Onodera learns that a 5000 carat diamond is being sunk into Lake Biwa, he believes that he can steal it and make up for the lost opal. Onodera's lover frees him from his binds, and he gets into his car and drives to Lake Biwa. Onodera steals a boat and rides it out to the boat carrying the diamond. He shoots one of the soldiers on the boat and holds everyone else at gunpoint, demanding they hand over they diamond. Onodera gets his hand on the diamond and takes it onto his boat. As Onodera flees, Barugon extends his tongue and grabs Onodera and the diamond with it, then swallows them both whole.

With all hope seemingly lost, Keisuke examines the remains of several missile launchers destroyed by Barugon's rainbow. He notices that the only things not vaporized by the beam are small mirrors. Using this, he proposes a new plan to the JSDF: the construction of a gigantic mirror that can reflect Barugon's rainbow back at him and fatally wound him. The JSDF puts the plan into action, creating a giant parabolic lens surrounded by several remotely controlled tanks. Barugon is lured toward the mirror, and the tanks open fire on him. Barugon retaliates with his rainbow, which strikes the mirror and is reflected directly back at Barugon, searing his flesh and causing him to collapse to the ground. Unfortunately, the wounds are not enough to kill Barugon, and he learns from his mistake and does not fire another rainbow. Just as Keisuke, Karen and the JSDF accept they have no way to stop Barugon, Gamera begins to thaw back in Osaka. He takes flight and flies to Lake Biwa for a rematch with Barugon. The monsters fight again, but this time Gamera gains the upper hand and throws Barugon into the lake. When Gamera realizes that the water injures Barugon, he clamps his jaws onto Barugon's neck and forcibly drags him to the bottom of the lake, where Barugon finally drowns and fires one last rainbow out of the lake as he dies. Gamera flies out of the lake and disappears over the horizon, leaving humanity safe from Barugon's reign of terror. Keisuke tells Karen he will take her back to New Guinea, as he now has nothing to live for and is completely alone after the death of his brother and best friend. Karen grabs Keisuke's hand and tells him that he isn't alone after all.