The correct answer is "Taro Aso".
In contrast to the other 3 rulers mentioned in the question, which were in fact dictators under a Socialist form of government, Taro Aso was the leader of the executive branch of government that operated under The Japanese Constitutional Monarchy. This political system acknowledges the reign of a noble leader (in this case, an Emperor), however, its power is very limited because it is shifted to a governing body of the official who is democratically elected by the people of Japan.