Series: Kamen Rider Black
Kyoko Akizuki is Nobuhiko's younger sister, targeted a number of times by the High Priests as her lifeforce could awaken Shadow Moon. At first she was not aware of Kotaro being Black until she was abducted by the Birugenia and saved by him. Once Nobuhiko emerges as Shadow Moon, she and Katsumi are terrified of his new appearance as she eagerly refuses his offer to join him in making a new world without violence. After the defeat of Black at the hands of Shadow Moon, she and Katsumi left Japan to start a new life abroad.
Katsumi is Nobuhiko's girlfriend, like Kyoko she is not aware of Kotaro being Black himself until Kyoko tells her the truth about Kotaro. Once Nobuhiko emerges as Shadow Moon, she was also terrified of his new appearance. She assists Kotaro quite a few times to persuade Shadow Moon to remember his human-side. After the defeat of Black at the hands of Shadow Moon, she and Kyoko left Japan to start a new life abroad.
Taki Ryusuke is an Interpol Agent from America. He assists Kamen Rider Black twice in defeating Gorgom. Taki Ryusuke appeared in episode 16 and 30.
A group of children who appeared twice in the series to assist Kamen Rider Black in defeating Gorgom. They were actually much older than they looked as Gorgom had made some alterations to stop them from growing. They managed to rebel and escape from Gorgom where they later joined forces with Kamen Rider Black. They appeared in episode 24 and 31.
Masaru Todou is Kotaro's senior in university and owns a shop called Capitola, where Kyoko worked during the day part-time.
Yoichi Daimon is a scientist who was recruited by Gorgom to create the Road Sector before the High Priests gave orders for mass production for their plans of world conquest. Convinced that the bike shouldn't used for evil means, he hid it in a safe place. When Gorgom discovered it, they sent the Bat Mutant to kill him and Hotaru, wife of his son Akira Daimon. Akira hid in the mountains and trained his son Kenichi on how to ride a motorbike in order to master the Road Sector. Akira gave possession of the Road Sector to Black to use for the good of mankind after he defeated the Longhorn Beetle Mutant and saved Kenichi from Baraom and the Bat Mutant.