The plot involves an alien empire from the planet "Dada" called the "Robot Army Corps". When they kidnap a human scientist, Dr. Hayami, and two of his three sons and force him to improve their technology, he has no choice but to go along with them, despite his deep anger, resentment, and guilt.

One year later, their empire sufficiently advanced, the Robot Army Corps return to Earth, ready to put their plans into action-- however, two heretofore unknown robots charge in and stop their invasion cold. It is then revealed that Dr. Hayami programmed the personalities of his two kidnapped sons, Jouji and Ryouji, into these super-powered robots to both stop the Robot Army he was forced to work for, and care for his youngest son, Kenji. Jouji and Ryouji, now "Skyzel" (as in "sky) and "Granzel" (as in "ground"), are armed with awesome strength and powerful shape-shifting abilities, able to transform into a jet and a car respectively. With these abilities, they carry on their father's legacy and fulfill his wishes.