A mysterious disease kills most of young males in feudal Japan. Women are forced to assume male work and the political rule of the empire. The male which are still alive sell their bodies for sexual intercourse or are used by their parents (usually the mother at the anime) for making money as a reproductive being. This last phenomena is explained by the desire of women of all social classes to get pregnant, because marriage and stable relationships are not possible anymore. As the society "protects" men from the disease, males become lazy, useless, weak and dependent.
Although the anime seems to have a feminist plot at the first glance, it can be read from another viewpoint. There is a balance between masculine and feminine "energy" in any society. When something disturb this balance, consequences are inevitable. At the anime, as men are lacking as workforce, women are fully capable of taking the job, but at a higher mental and physical cost. Be an independent and strong women do not resolve the loneliness of a life whithout a partner or family. Power, not gender rules the world, and the women in command (lady Kasuga) will force another women (lady Iemitsu) to suffer and be sexually ubused in order to keep political domination.
Comparing to the anime, in our real world, a "mysterious" disease is trying to kill the masculine spirit. As occurs in the anime, men are becoming lazy, weak, dependent and afraid. Our society is starting to feel the consequences of this.
In resume, the anime can be viewed as a reflexive story of the necessity of the harmonic balance between feminine and masculine. Man and woman need to work together for the development of humanity.