I know Japan actually did have Empresses before. Actually before Japan had much influence from other countries, like China for example, there was a great respect for women and also I believe there was more women in power during that time. Considering that unlike most cultures who like to associate their ruler with a god, Japan's royal family is said to be descendents of the Sun Goddess, Amaterasu.
I could be wrong or inaccurate at some or many points, seems my memory is a little fuzzy ^_^;;;