Six months after the events of the previous Gamera adventure, a meteorite collides with the Z Plan rocket and frees Gamera, sending the giant creature back toward Earth to unleash new devastation as it targets the Kurobe Dam in Japan. Gamera Teruo Aragaki returns with a renewed menace, forcing a nation to confront a familiar threat while the world watches and waits for a plan to save cities from another catastrophic encounter.
In the midst of this crisis, Ichiro Shō Natsuki, a World War II veteran, devises a perilous rescue mission. He sends Kawajiri Yūzō Hayakawa, Onodera Kōji Fujiyama, and his brother Keisuke Kōjirō Hongō to the remote island of New Guinea. The goal is to recover an opal that Ichiro once discovered and hid, a treasure that promises more than wealth if it can unlock ancient secrets. The jungle proves to be as dangerous as any enemy, and the trio faces warnings from wary local villagers who sense a hidden danger beneath the stone they seek. They push forward, driven by a mix of loyalty, curiosity, and the hope that this opal could hold the key to stopping the monster’s latest rampage.
The expedition is cut short when Kawajiri falls to a fatal scorpion sting, a sudden reminder of how fragile life is in the wild. Keisuke is then betrayed by Onodera, who turns violent and nearly takes Keisuke’s life as the jungle consumes them. Keisuke is rescued by the locals and, while recovering, he confides in Karen Kyōko Enami about the opal and the perilous journey he has endured. Karen quickly discerns that the “opal” is not a jewel at all but a trap that could unleash far more danger if taken to Japan, and she persuades Keisuke to bring the truth back home.
The voyage continues toward Japan, but a twist of fate alters everything. Onodera accidentally leaves the opal exposed to infrared light, and the intense heat incubates it—revealing that the opal is actually an egg. From the egg hatches Barugon, a formidable reptilian creature whose emergence sets off a new cascade of chaos. When the ship finally reaches Kobe Harbor, disaster erupts as the ship is destroyed, and Onodera reveals a grim confession: he killed his two companions and murders both Ichiro and his wife to cover up his crime. The revelation triggers a fierce confrontation as Barugon rises from the harbor to begin a city-spanning rampage.
Barugon’s rainbow ray becomes a beacon that draws Gamera into a climactic clash, their battle electrifying Osaka with force and fire. Barugon’s power freezes Gamera in place, complicating the struggle and forcing the human defense to rethink its approach. Keisuke and Karen reunite and propose a bold tactic: use a colossal diamond to irradiate Barugon enough to lure him into a lake where he could be drowned. The plan, however, is hampered by the diamond’s radiation limits, and a second attempt to boost the effect with infrared irradiation nearly works—until Onodera seizes the gem, his desperation sealing a deadly fate as Barugon devours both him and the diamond.
With the diamond damaged and their options dwindling, the defense ministry pivots to a countermeasure grounded in physics and ingenuity. Keisuke discovers that Barugon’s rainbow ray is not affected by ordinary reflections, but mirrors can redirect the emanation back toward the creature. A massive mirror is deployed, and the plan finally gains traction. Gamera breaks free from his icy prison, renewing the fight against Barugon as the two colossal beasts collide again. The confrontation culminates with Barugon being drawn into Lake Biwa and drowned, his threat neutralized by a combination of science, courage, and a bit of luck.
In the aftermath, Keisuke mourns the cascade of greed and ambition that set these events in motion, leaving him to reckon with the costs of the choices that brought such catastrophe to the world. Karen steps in to offer solace, taking his hand and reminding him that he is not alone—an intimate moment that underscores a quiet, human resolution amid the spectacle. The city may have survived, but the story remains a meditation on danger, responsibility, and the enduring bonds that help people weather even the worst revelations.
