A mad scientist known as Dr. Shida builds a robot in the likeness of his wife. However, as Godzilla and Anguirus return, he also builds a giant feminine robot, "Robot Daughter," in the image of his foster daughter to fight them. Adding to Dr. Kyohei Yamane's thesis from the original Godzilla film where Dr. Yamane explains Godzilla went undetected for so long because he lived in trenches, Dr. Shida proposes that Godzilla and Anguirus lived so deep into ocean trenches that they come from the center of a hollow Earth.
Inside the hollow Earth, Dr. Shida finds many Godzillas, Anguiruses, and a race of beautiful mermaids. He falls in love with one of the mermaids. During a fight between Godzilla and Anguirus, a giant blood-sucking flea is lodged from Anguirus' shell. Then, Godzilla, Anguirus, a Giant Chameleon and a Giant Archeopteryx appear in Kyushu.
Robot Daughter is finished and is sent to defend Japan. She defeats the Giant Chameleon, the Giant Archaeopteryx, breaks Anguirus' jaw and then faces Godzilla. Robot Daughter is unaffected by Godzilla's atomic breath. Godzilla seems to fall in love with Robot Daughter, and goes in a cave with the naked Robot Daughter. One character says "...it is the foreplay of love to be beaten."
Robot Daughter turns out to be a timed hydrogen bomb and takes Godzilla back to his ecosystem before exploding, destroying the ecosystem in the center of the Earth and presumably ending Godzilla.
Bride of Godzilla was considered as a follow-up to Godzilla Raids Again. The film's script was written by Hideo Unagami, who also wrote The H-Man. The film's cancellation was likely due to Godzilla's creators feeling that they shouldn't make another quick sequel like with Raids Again. The Giant Archeopteryx was probably a predecessor to Rodan.
Robot Daughter does not have an official name, and its nickname, 'Robomusume,' is fanmade.
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