The Creation King was the one who ruled the entire universe and every fifty thousand years, his life would come to an end. Before that happens, a new Creation King must be chosen and the Gorgom, a dark and evil organization, is the one to decide so. Nineteen years ago, Minami Kotaro and Akizuki Nobuhiko were born on a day of a solar eclipse. Three years later, Kotaro's parents were murdered by the Gorgom. The Akizuki family took Kotaro in and treated him like their own family member. Kotaro and Nobuhiko grew up together like brothers. On their 19th birthday, Gorgom abducted them both. They were transformed into cyborgs and erase their memories for Gorgom to choose a new Creation King between them. The present Creation King gave Gorgom two magical Kingstones. After the operation, both young men were officially called 'Century Kings.' The main deal was to make both Century Kings fight each other and the winner become the new Creation King.

Professor Akizuki, Nobuhiko's father, who also happened to be one of Gorgom's scientists, didn't want Gorgom to erase away his children's memories of him. Professor Akizuki interfered in the operation, giving the perfect opportunity for both Kotaro and Nobuhiko to escape. Kotaro managed to escape but not Nobuhiko, who got electrocuted during the interruption of the operation. A Kingstone had already been fitted into Kotaro's body. The evil Gorgom tried to get back the Kingstone from Minami Kotaro. Our hero soon realized that the Kingstone in his body had special and unique powers. Abandoning the name Black Sun, a term which was given by Gorgom for his cyborg form, Kotaro called himself Kamen Rider Black, Kotaro made full use of the Kingstone's powers to transform himself into Kamen Rider Black. With that power, he battled Gorgom and its monsters and hoped to rescue his brother, Nobuhiko one day.