Prime Minister Shinzo Abe has sought to have women hold 30 percent of supervisory positions in all fields by the time Tokyo hosts the Olympics in 2020. But as of now, his own government is at least 15 years behind schedule.

Women fill just 6.2 percent of junior management jobs in the nation's bureaucracy. While the intake of graduates is now more than 30 percent female, careers tend to progress at a snail's pace. It takes about 20 years' tenure to move into a supervisory role, meaning the new cohort of women starting work on April 1 will likely be kept waiting until the mid-2030s. Hitting the target for senior management will take even longer.

"It's different from the U.K. or the French professional bureaucracies where, if you are really good, you can get a big job in your 30s or 40s," said Robert Dujarric, director of the Institute of Contemporary Asian Studies at Temple University's Japan campus. "Everything's decided by seniority. Good people languish in lowly jobs for decades."