Godzilla vs. Gigan (1972)

Freelance manga artist Gengo Odaka applies for and gets a job as a designer for Tokyo's World Children's Land, a theme park whose key attraction is a life size replica of Godzilla dubbed Godzilla Tower. Right away Gengo notices several peculiar things about his employers. His boss, Kubota, obsesses over world peace despite hiring Gengo to design new monsters for the park. According to Kubota, it's the plan of their organization to create full scale models of the monsters on Monster Island before ultimately destroying it and its inhabitants. The organization's Chairman is a 17-year old boy named Fumio Sudo; when Gengo first meets him Sudo is nonchalantly charting interstellar coordinates, including the orbit of the M Space Hunter Nebula.

On his way to the office one day, Gengo bumps into a young woman. She scrambles off in a hurry but leaves behind a roll of magnetic tape which Gengo subsequently hides from Kubota and other pursuers. Gengo learns from the Chairman that this girl is an "enemy of peace" who's scheming to foil the park's plans. Later that night, Gengo is stopped by the young woman. When Gengo refuses to return the tape to her, her companion holds him up with a corncob. Believing it to be a gun, Gengo faints. He awakens at home with the two bandits taking care of him. As it turns out, they are really Machiko Shima and Shosaku Takasugi. Machiko's interest in Children's Land stems from the disappearance of her brother Takeshi, a computer technician for the organization. The tape, she believes, might hold the key to his whereabouts. Gengo determines the duo is telling the truth and he decides to snoop around the Godzilla Tower for clues.

Gengo manages to find Shima locked in a room in the Tower and briefly contacts him but in doing so he arouses suspicion from Kubota. The trio decides to investigate the park's origins as well as the histories of the Chairman and Kubota. Meanwhile, they play the stolen tape on Gengo's reel-to-reel player but it produces only unintelligible electronic noises. The signal is picked up by the Tower's computers; the Chairman orders a change of the "Action Signal Tapes." The signal is also heard by Godzilla and Anguirus on Monster Island. Godzilla, realizing the potential danger, orders Anguirus to Japan for reconnaissance.

During their investigation, Gengo and Shosaku discover that both Sudo and Kubota had apparently died exactly one year prior in a mountain climbing accident. The identities of the deceased are confirmed when Gengo examines a photograph of them. They are physically identical to his bosses. Anguirus, meanwhile, is repelled from Japan by the JSDF.

Cigarettes given to Gengo by Kubota allows Children's Land personnel to track Gengo to his apartment where he's meeting with Shosaku and Machiko. The intruders are driven off by Gengo's girlfriend Tomoko Tomoe, a black belt in karate. The group is turned away from the police who don't believe their suspicions so they hatch a plan to break into the Tower and sneak Takeshi out under cover of night. The plan ultimately backfires and Gengo and Tomoko are captured. Kubota reveals that the Children's Land staff are aliens from the M Space Hunter Nebula and that their ultimate goal is to take over the Earth. Godzilla Tower was built to kill the real Godzilla, but the aliens are using their tapes to command the space monsters Gigan and King Ghidorah to level Tokyo. The earthlings' lives are spared so that their bodies can be used as "uniforms" for the alien invaders who are nothing more than giant sentient cockroaches.

Godzilla and Anguirus depart Monster Island to combat the invasion. The space monsters arrive in Tokyo first and begin laying waste to the city. While the aliens are busy controlling the monsters, Shosaku and Machiko send a weather balloon up the side of the Tower to allow the captive humans to escape. After observing that the aliens are incapable of diverting from their taped plans, Gengo and Takeshi enlist the aid of the JSDF to infiltrate the Tower.

The defending Earth monsters arrive in Tokyo Bay and immediately engage the space monsters in battle. Gigan proves to be a savage opponent for the King of the Monsters and successfully uses an aerial buzzsaw attack to critically injure Godzilla. Gigan's attacks put Godzilla in range of the Godzilla Tower's laser beams, which prove immensely effective against the real Godzilla. Anguirus too is injured by Gigan's saw.

Gengo quickly draws a life size sketch of his group which the JSDF uses to hide several crates of TNT in the Tower's elevator. The elevator reaches the top floor and the aliens, not realizing the trap, shoot the crates. The resulting explosion destroys the Tower and breaks the control over the space monsters, leaving them disorganised and confused. Gigan comes to his senses first and pummels the weakened Godzilla; together with King Ghidorah, the monsters push Godzilla into the remains of the Tower. But in an instant Godzilla's strength returns and the tide of the battle quickly turns in favor of the Earth monsters. Their counterattack separates the alien monsters and Godzilla uses his atomic breath to keep Gigan out of the sky. With certain defeat approaching and no more orders to follow, the alien monsters retreat to space. Godzilla and Anguirus return to Monster Island to the cheers of Gengo and his friends.