A monster rampages through Tokyo. Eventually, it is killed by a big missile. Afterwards, the authorities make a startling discovery: the monster was a mother, and its infant is still very much alive! The Japanese government decides to name the baby "Daigoro" and raise it to be friendly to humans, so that humanity will have a monster ally to pit against any kaiju threats that arise in the future. A few years later, Daigoro has grown into ... something indescribable. He looks like a leapard seal's head on top of an accordion. Daigoro eats a lot (he seems to be a vegetarian, interestingly enough) and his appetite has bankrupted the agency charged with caring for him. Anyway, after a lot of unendurable "comedy" where fans of Daigoro (mostly children) try to con greedy businessmen out of donations to his food fund, plus some awful s**t about a fat guy trying to woo the slutty niece of an inventor, Goliath finally arrives. He kicks Daigoro's ass. I mean, come on, Daigoro is probably the monster equivalent of fourteen or fifteen. He's just not ready yet. Obviously, this means Daigoro's handlers will have to train him in karate! More "comedy". Daigoro fights Goliath again, this time winning because he's learned how to breathe fire - just like his Ma! I don't know what happens in the last few minutes because I turned the damn movie off.
Reportedly, this was originally to be a Godzilla film ... sort of. Eiji Tsuburaya approached Toho with an idea to kill off Godzilla and start a new series of kid-oriented films focused on Godzilla's son, Minya. Godzilla wasn't as profitable as he used to be, plus it was the tenth anniversary of Tsuburaya Productions. The publicity from killing off the character that made him famous and setting up a new franchise would be a win-win for both Tsuburaya and Toho. It was not to be. After going through development hell, Tsuburaya's idea mutated into Daigoro vs. Goliath. On the one hand, I'd sort of like to know how The Son of Godzilla vs. Goliath (and any sequels) would have turned out. On the other, the 70s Godzilla movies are my favorites, so I'm glad the Big-G stuck around until 1974.
The biggest problem with Daigoro vs. Goliath is that's almost a damned Michael Bay movie. The monsters are barely more than props while the vast bulk of the movie is devoted to shallow stereotypes posing as characters having wacky misadventures. We've got Annoying Kids, an Animal Lover, an Unreasonable Boss, a Bossy Big Sister, an Absentminded Inventor, a Fat Guy, and a Fat Guy's Shrewish Wife. You'd damn well better find those character archetypes amusing because for about 90% of the movie, that's all you're going to get.
When the monsters are around, the movie gets a little better. Daigoro himself is sort of interesting. He was raised by humans, can understand what they say, is able to tell when he's being lied to, and is even capable of make moral decisions. For instance, scientists invent "anti-grow" to keep Daigoro from getting bigger and needing even more food. Daigoro doesn't fall for it when Unreasonable Boss tries to trick him into eating it. When the full situation is explained to him, however, Daigoro tearfully eats the anti-grow, understanding what a burden he has become to his human friends. Goliath ... eh. He doesn't get enough screen time to amount to anything but a punching bag for Daigoro. Daigoro's mother ... eh. She doesn't get any screen time, either.
With more time devoted to the monsters and less to the horror of a fat guy mugging for the camera while some annoying kids beg rich people for money at the same time an inventor almost hangs himself on a robot arm simultaneous to his slutty, overbearing niece belittling him, Daigoro vs. Goliath might have been mostly ok. As it stands, the movie is little more than a curiosity for true devotees of giant monster cinema.
Note: Unreasonable Boss is played by the same guy who was mentor to most of the early Kamen Riders.