I think my friend was wrong in labeling Kappa a character study, unless he means of the author (and you could make a good case on that front); the book is more social satire, with an underground kingdom of kappa subbing for 1920s Japan. The book was translated and brought to America in 1947, which means that the whitebread baby boom was confronted with this image of the kappa birth process:
But when at last the child is about to come out,the father puts his mouth at the ... of the mother [... the book's, not mine] as if he were on the telephone, and asks in a loud voice:
"Do you wish to be born into this world? Think it over and give your answer."
And if the answer is "no":
...the midwife in attendance quickly inserted a big glass tube in the ... of [the] wife and injected some liquid. She heaved a deep sigh of relief, and at the same time her belly, which had been so big, shriveled up like a balloon emptied of its hydrogen gas.
Yeah, I can't imagine what Truman America thought of that.
Then there's the kappa political speech where the human narrator points out the speaker's lies only to be told by his enraptured kappa friend: "Come now...That speech of his is of course a lie, every bit of it. But everybody know that it's a lie, so it's an honest speech after all, isn't it?" Kappas also create the "Worker Butchery Law" as a solution to unemployment, whereby the shiftness, good-for-nothing out-of-work laborers are made useful to society by being repurposed as food. I'm surprised a Worker Butchery Law hasn't been proposed to wild applause at the Republican debates, quite frankly.
The book has incidents that hit home, but there's no...sensible through-line to it, I guess? It's not like Alice in Wonderland, a travelogue with some transition; it's just...not very much transition at all. Part of the problem might be the older translation, released in an era when Japanese-English translation wasn't fully developed as at art; it's not bad, just stilted in places. I still get the feeling, though, that I'm missing something here, so I'm afraid this has to go down as a big "?" in my books for the moment. Maybe I need more Akutagawa under my belt.