The whole darkness of this book almost took me over when I was reading it. It's a real page-turner and Kirino's language is absolutely beautiful. It's very powerful, very fluid, with almost a strange kind of lyricism about it.
One of the author's very strong points is that even though it's a very dark, gruesome, unsocial world they live in, she believes very much in human relationships, especially between women. The solidarity that they experience, and how it can empower some of them to get out of their situations, is the important point here.
The four main characters really do represent four types of women in Japan. The first, Masako, is a very capable businesswoman who cannot get ahead of her social status in the company because she's a woman. Then you have Kuniko, who is the epitome of the bubble economy of the late eighties. She spends money like there's no tomorrow and she's worse off because of it. Yoshie looks after her mother-in-law in an old wooden house, meaning a very poor background. Finally, there is Yayoi, who's the stay at home mother while her husband is the breadwinner. This is a new Japan where the old family relationships are breaking down because this is the new world, and women have to work.
Her other minor characters are people who are very much on the margins of Japanese society. She has the Chinese hostess working in Tokyo and the Brazilian with a Japanese father coming back to Japan (called Nikkei-jin). She has these foreigner segments of society mixed in with what you'd assume to be mainstream Japanese society. She uses these minor characters to really ignite some of the main themes of the book.