The Gaira aliens, concealed in the Arctic, intend to conquer Earth. Dr. Yan, captured and compelled to labor for the invaders, constructs the ultimate weapon: a transformable aerial robot named Groizer X. Entrusting the machine to his daughter Rita, he ensures Groizer X escapes the Gaira's grasp and lands in Japan. There, pilot Jo Kaisaka encounters a wounded Rita. Assuming control of Groizer X, Jo and Rita battle the Gaira invasion.