Demeking the Sea Monster is sold as a kaiju film, but that's really stretching it. There is a giant, city-destroying monster involved, but it's seen for about as much time as Clover is. And like Cloverfield, and Monsters next year, this is more about people that the monster, or at least the prophecy of the monster, impacts than the monster itself. Demeking is really a story of a couple of disaffected people, with a ten minute kaiju sequence thrown in. Further, Demeking is referred to as a space monster in the film, not sea monster any more than Kraa the Sea Monster turned out to be.
In the openning, Hachiya drives among a blighted industrial landscape similar to the one from All Monsters Attack. This gives the audience a sense of time. 1970, when Japan's industries were indifferent to pollution, the era when Godzilla vs Hedorah was made.
The majority of the action happens in 1970, when our protagonist, Kameoka, is in high school. Kameoka is socially awkward, dislikes school, and would rather hang out with his middle-school aged friends, forming the Tanoura Exploration Club. Anything to get away from his dreary reality. The film has some notes of Gamera the Brave, with the bored kids trying to make their own fun, but Gamera had more focus.
The town has a dreary little fun park, but it seems as listless as everything else. But When Kameoka meets Hachiya, Hachiya reveals that he has a desting. To fight Demeking. Hachiya could become the head of the club if he wanted it. He has a motorcycle. When he suddenly leaves for Tokyo, however, he leaves behind a treasure hunt for the boys. And suddenly, thre's magic in their lives. Something to investigate, something to to. Something unknown.
In the end, they come up with a large banner. When spread out on the beach, is says "Space Monster Demeking Witness Koichi Hachiya, 2019" With a large painting of a footprint, a clever subversion of the giant footprint trope that goes all the way back to the black and white King Kong.
It's difficult to portray boredom in a film without boring the audience. Demeking is mostly successful. The pace is leasurely, with many shots of the fun park's Ferris wheel turning lazily, and many scenes of Hachiya and Kameoka doing dull or repetitive things. Anyone coming expecting a giant monster trashing Japan is going to be sorely dissappointed, and the marketing of the film as a kaiju work doesn't help. I'd read a few reviews and knew what to expect, but someone who picks up the film because the tag line is "Terror Lies Beneath" is going to be sorely dissappointed.
Demeking arrives, like Ghidorah, in a meteor. And I wonder if there isn't a certain amount of influence from King Ghidorah. Demeking is best described as a huge, walking snail with a barnacle cluster for a shell. It has a breath weapon, which it uses to destroy the oil refinery it landed in (shades of Gamera) because without another monster to fight, what else is there to do with a breath weapon?
Demeking blazes a trail of destruction, and in its wake, it leaves dozens of eggs. Kameoka chases it down, confronts the creature, only to wake up. It was a dream.
Two years later, Kameoka meets his buddies again. He is still in high school, but he's writing a novel about Hachiya and Demeking. In a piece of truth in fiction, he is more enthusiastic about telling people about it than he is in actually writing it. The last we see of it is Kameoka's empty desk. Has he given up? Or was the novel finished? Haochiya has taken several part-time jobs, but he's still dissaffeced and aimless, even though his father tries to get him to take his life seriously.
Demeking uses its kaiju in a very dfferent way than other films. The creature is more a subplot in the film, a dream Kameoka has. TV Topes calls this Rent-a-zilla, where the kaiju appears, but itn't the full focus of the film. The most famous example is probably the Stay-Puft marchmallow man from Ghostbusters. As it gets easier to put CG into films, it gets easier to introduce a kaiju this way. Unfortunately, the English marketing team seems to have latched onto this as the main feature of the film.