Invasion of Astro-Monster

In 196X, astronauts Fuji and Glenn arrive to investigate the mysterious Planet X. They are ushered into an underground Xilien base where they meet the Controller. The encounter hints at a fragile alliance and foreshadows the danger looming over Earth.

Monster Zero, later identified as King Ghidorah, assaults the Planet X surface. The Xiliens present the creature as a formidable ally against Earth, masking their true intentions. The astronauts witness Ghidorah's fearsome power up close.

The Controller offers a deal: protect Planet X by borrowing Earth monsters Godzilla and Rodan in exchange for a cure for cancer. The proposition reveals the aliens' willingness to exert control over Earth’s most powerful forces. It exposes the moral ambiguity of their seemingly benevolent façade.

Back on Earth, inventor Tetsuo has created a personal alarm that emits a piercing sonic blast. He sells it to Namikawa, who disappears before paying him. Fuji disapproves of Tetsuo's romance with Haruno, doubting his worth.

Three Xilien spacecraft land in Japan, triggering fears of a wider invasion. The Xiliens locate Godzilla and Rodan and transport them to Planet X using their technology, bringing Glenn, Fuji, and Sakurai along. A brief confrontation follows, and Ghidorah is driven back.

On Planet X, the astronauts are brought before the Controller and sternly reprimanded, though not punished. Xilien guards then capture Glenn, Fuji, and Sakurai, locking them in separate cells. The fate of Earth’s champions seems grim as the aliens tighten their grip.

Glenn encounters Namikawa in Xilien garb and learns she is one of the aliens' spies who has fallen in love with him. She is executed by her commander for the emotional breach, but not before slipping a note into Glenn's pocket. The note hints at the Xiliens’ weakness.

Glenn and Tetsuo escape with the aid of Namikawa's note. Tetsuo activates his sonic prototype, weakening the Xiliens’ electronics and enabling their flight to freedom. They slip through the corridors and rejoin Sakurai and Fuji, continuing the plan.

Sakurai and Fuji build a device to disrupt the Xiliens’ control over the monsters. Glenn and Tetsuo share the aliens' weakness and help coordinate the plan. They broadcast a sonic disruption over the radio, cutting the Xiliens' grip just as Ghidorah and the Earth monsters reassert themselves.

With their control shattered, the Xiliens destroy themselves en masse. The monsters awaken from their trance and clash again, turning the tide of battle. Ghidorah is sent toward the ocean and retreats to space, while Godzilla and Rodan are presumed alive.

Fuji acknowledges Tetsuo's crucial role in the victory and stops doubting him. Sakurai proposes sending Glenn and Fuji back to Planet X for thorough study of the planet. The team is relieved that Earth is safe and begins to weigh future scientific opportunities.

The expedition plan concludes with a sense of cautious optimism: Earth remains safe for now, and further study of Planet X is proposed. Glenn and Fuji consider the possibility of returning for deeper exploration, while the immediate threat has been neutralized.