Haruna Saeki is a giant heroine and Lady Mars, hiding her true identity while working an ordinary job at a factory. One day, the Mozz aliens attack the facility, using waste tanks to cultivate seeds of Gedora in their plan to invade Earth. Having assimilated into human society, Mirai is unable to transform and fights the Mozz aliens in her human form, but is struck by Gedora's growing rays and dies. At that moment, the Mars warrior Kwai Mars appears, entrusting Mirai with the mission to fight once more as a warrior. Revived, Mirai transforms into Lady Mars and battles Gedora, but ultimately meets a tragic bad end.