Godzilla vs. Megalon

In early 1971, the second of a series of underground nuclear tests is conducted near the Aleutian Islands. The shockwaves travel across the Pacific and reverberate through the sea to Monster Island, damaging the island paradise. The event foreshadows a threat from the depths that will rise soon.

Seatopia, a wealthy undersea civilization, has existed in relative peace for millions of years. Nuclear tests have crippled their cities with earthquakes, prompting Emperor Antonio to seek revenge. They plan to unleash Megalon, their beetle-like god, to destroy the surface world.

Goro Ibuki, his little brother Rokuro, and their friend Hiroshi Jinkawa are on a peaceful outing by a lake. Seatopia reveals itself by draining the lake and using it as a staging area. The trio's routine day becomes the prelude to disaster.

On the return trip, Seatopian agents ambush the trio to seize Jet Jaguar, the humanoid robot they are building. The first attempt ends in a botched escape for the agents, forcing them to retreat. The incident marks the first direct clash over the robotic project.

Jet Jaguar is completed, but the Seatopian agents return and knock the inventors unconscious. The heroes are captured, and Jet Jaguar is left under the enemy's influence. A new threat emerges as Megalon becomes a tool of Seatopia.

With Jet Jaguar under their control, Seatopia commands Megalon to destroy a surface city. They mark Goro and Rokuro for death and take Hiroshi hostage to ensure obedience. Megalon's path begins toward Tokyo, backed by Seatopian forces.

Megalon is released to the surface and directed by Jet Jaguar, now under Seatopian control. The JSDF struggles to stop the rampage as Megalon tears through the outskirts of Tokyo. The clash threatens widespread destruction on the city.

Goro, Rokuro, and Hiroshi escape from their captors and reunite as a team. They band together to find a way to enlist Godzilla's help, planning to use Jet Jaguar's secondary control to reach him. The escape marks a turning point in the battle's direction.

Goro regains control of Jet Jaguar with help from Japan's Defense Force. Jet Jaguar is sent to Monster Island to recruit Godzilla for aid against Megalon. The plan shifts the conflict from Tokyo to a two-front struggle against Megalon.

As Jet Jaguar acts more autonomously, it grows to gigantic size to face Megalon. Godzilla is en route to the battlefield, joining the struggle against Megalon and Gigan. The duel intensifies as two giant heroes prepare to contest Megalon.

Nebulan allies send Gigan to assist Seatopia. Gigan and Megalon press their advantage against Jet Jaguar, creating a tense three-way fray. Godzilla's arrival remains imminent as the balance of power shifts.

Godzilla arrives and teams with Jet Jaguar to counter Megalon and Gigan. After a brutal clash, the foes retreat and the heroes celebrate their hard-won victory. Jet Jaguar bows out, and Godzilla heads back to Monster Island.