Set in a near-future Japan after its society became completely dominated by women due to the rampancy of radical feminists and the country introducing the "Gender Segregation Act" decades ago, you are Katagiri Yui, originally a child soldier in the defense forces who eventually got to hid in a remote village under a fake identity, who is ordered by Mother, an social management AI, to attend the training school of the Security Force, a women's armed forces with your adoptive sister.