Sakie Fukushima remembers the novelty of being the only woman on Korn/Ferry International's board of directors, which she joined in 1995. Ditto when she joined the Sony Corp., Kao Corp. and Benesse Corp. boards years later.

Even now, three years after Prime Minister Shinzo Abe made increasing women's participation in the workplace a tenet of his prescription for reviving Japan's fortunes, the proportion of females on Japanese boards has hardly budged — at around the lowest in the developed world. While companies strive to follow Abe's lead and narrow the gender gap, there's a confluence of obstacles so deeply rooted in Japan that overcoming them may take another generation.

"It's not politically correct anymore to oppose putting women on corporate boards, even in Japan," said Fukushima, 66, now a director of several companies including Bridgestone Corp. and Mitsubishi Corp. "Companies want to put women on their boards. Yet there are not enough candidates among women here, with the board experience needed."