Sahara Family
The Sahara Family are the ones who took in Kotaro and gave him a job in their helicopter business Sahara Airlines. Shunkichi and Utako are the parents who are always arguing with each other, Shigeru is their son, and Hitomi is their daughter. The parents are murdered by Jark Murder in episode 46.
Reiko Shiratori
Reiko was Kotaro's girlfriend. She was also a photojournalist, she helped him before and after learning he is RX. After learning that Kotaro is RX, she begins to train herself in order fight Crisis's minions.
Joe the Haze
Joe the Haze is a master of the fighting style Haze Kenpo. He is one of Kotaro's closest friends and considered just as close as he was to Nobuhiko. Joe was originally a human from Earth who willing allowed the Crisis Empire to convert him into a cyborg, losing all memory of his past and actual name. Under the control of Necksticker, Joe attacked Kotaro during his attempt to save Hitomi, becoming his ally once he regained his mind. He ended up injured by Bosgan during RX's fight with Gynagingam. He soon recovered and came back to help Kotaro.
Kyoko Matoba
Kyoko Matoba is an ESP girl who is skilled with a bow and can manipulate ground water. Her parents were murdered by the Crisis Empire monster Mundayganday, helping RX fight the Crisis Empire. Before specifically manipulating water, she was able to control all sorts of things in nature such as plants and rocks.
Goro is a chef who works at Sahara Airlines. He didn't fight physically against Crisis, since he was not a fighter. Since his specialty was in cooking, he helped to serve some delicacies for our heroes.
Hayato Hayami
Hayato Hayami is an inspector who pursues Kotaro, believing he's a troublemaker. He was last seen knocked unconscious by Maribaron when she uses him to arrest Kotaro for her.
10 Kamen Riders
Series:  Kamen Rider Black RX