Shutting Out the Sun: How Japan Created Its Own Lost Generation by Michael Zielenziger.
He's a foreign correspondent in Japan, and interviewed some recovering hikkikomoris for the book. Also talked to several therapists and social workers who are struggling to deal with the hikkikomori phenomenon in the face of a government and society that largely pretend the problem doesn't exist.
Zielenziger then goes on to use hikkikomori as a metaphor for a contemporary Japan still trying to claw its way out of recession. Fascinating book, really.