Recently much attention is being paid in Japan to the so-called "parasite singles," grown children in their 20s and 30s who have left school and gotten jobs but are still unmarried and living at home with their parents.
The sociologist Yamada Masahiro coined the term in 1997 (inspired by the best-selling novel and movie "Parasite Eve"), and late last year he published an interesting nonfiction book on the topic, "Parasite Single no Jidai" (Chikuma Shinsho). In it he seems to at least in part blame such twenty- and thirtysomethings for everything from the falling birthrate and economic recession (because they are not establishing independent households and spending on housing and durable goods) to cultural stagnation (because they are focused on consumption and their personal lives with little interest in political or social change and reform).
Yamada notes the prescience of the mystery writer Uchida Yasuo in 1981 when he started the Asami Mitsuhiko mystery series with a parasite single as his amateur detective. The unmarried Asami is in his mid-30s but works as a freelance writer and lives together with his mother and elite policeman elder brother. He enjoys an affluent lifestyle and depends on his mother and sister-in-law for all his domestic needs.