After being kidnapped by the cult Gorgom on the night of their 19th birthday, stepbrothers Kotaro Minami and Nobuhiko Akizuki are submitted to a mutant surgery with the purpose of becoming the candidates to be the next Creation King. Kotaro escapes before the brainwashing, with help from his foster father, and turned against Gorgom. He soon finds out the horrific truth from his stepfather: Gorgom originally killed his true parents. Later on, Kamen Rider Black must battle with his brother, who has become the trump card of Gorgom, Shadow Moon.