Concealed within the Arctic, the Gaira aliens hatch their scheme to take over Earth. After being kidnapped and coerced into their service, Dr. Yan constructs the supreme weapon: Groizer X, a transformable aerial robot. He entrusts it to his daughter Rita, who manages to flee from the Gaira and crash-lands in Japan. There, pilot Jo Kaisaka encounters the wounded Rita. Taking command of Groizer X, Jo joins forces with Rita to resist the Gaira invasion.