Rosenbluth, Frances M., and Michael F. Thies. 2010. Japan Transformed: Political Change and Economic Restructuring. Princeton: Princeton University Press.
This book may be a good summary of Japanese politics for the juniors in graduate school, for those interested in both historical background to recent changes. The authors not only introduce the principal topics of Japanese politics but also treat them in a well-considered theoretical argument, with particular emphasis on electoral system change in 1994.