For Japan, the crowning of Hiromu Nonaka as its top leader would have been as significant as America’s election of its first black president.

Despite being the descendant of a feudal class of outcasts, who are known as buraku and still face social discrimination, Mr. Nonaka had dexterously occupied top posts in Japan’s governing party and served as the government’s No. 2 official. The next logical step, by 2001, was to become prime minister. Allies urged him on.

But not everyone inside the party was ready for a leader of buraku origin. At least one, Taro Aso, Japan’s current prime minister, made his views clear to his closest associates in a closed-door meeting in 2001.

“Are we really going to let those people take over the leadership of Japan?” Mr. Aso said, according to Hisaoki Kamei, a politician who attended the meeting.

Mr. Kamei said he remembered thinking at the time that “it was inappropriate to say such a thing.” But he and the others in the room let the matter drop, he said, adding, “We never imagined that the remark would leak outside.”