Sougo Tokiwa, a high school student born in the year 2000, has always dreamed of becoming a king when he encounters a mysterious girl named Tsukuyomi, who hails from the future in a desperate effort to alter her dire future. She presents Sougo with an ominous warning "You will become the king of all time, Kamen Rider Zi-O, a demonic king destined to rule the world.”.