The blurb claims it "Reads like the script notes for American Psycho - The Holiday Abroad". This is a weird and weirdly promising thing to say about a novel. It's weird because American Psycho was originally a novel, so why not just say it reads like the sequel? It's weirdly promising because American-Psycho-the-film (unlike the novel) is actually good.
American-Psycho-the-film is good because you're not stuck inside the psycho's head the entire time. This is a relief, since the inside of a psycho's head is a very boring setting for a novel. As a setting, it is a stage without any entrances, a monad. Lacking empathy, the psychopathic sole director has no way to bring other characters into the action, which degrades into lonely repetition as a result.
American-Psycho-the-film doesn't have this problem, because the camera takes you out of Bateman's head. In In the Miso Soup, Kenji takes you out of Frank's. This lets the plot move, driven by Kenji's fear of Frank, who he might be and what he could do, and the reader's interest in Frank as a symbol and vehicle for Murakami's satire.
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The violence of In the Miso Soup is a boring kind of violence. Frank's violence is force, in Weil's sense. It overwhelms its victims, it turns people into things. In the Iliad, this force is not boring, because its victims were as gods the page before. In Blood Meridian, this force is not boring, because the Judge in his ambition aims to make a thing of the entire world.
Frank's victims (salarymen and prostitutes) are not so godlike, and his ambition (if he has any at all), is not so grand, so his violence is boring, even if it shocks you as it bores you. Scenes of this kind of violence, like the scene in the hostess club, depicting only things, are ultimately varieties of still life, or, at larger scales, landscapes.