A robot dog that guards the Silver Carcass. He was built by Dr. Koga before Metalder as his "older brother". Capable of human speech, he repairs Metalder and runs the machines inside the Silver Carcass. Springer enjoys watching TV, particularly anime.

Mai Ogi
A tomboyish camerawoman who works for the Weekly Up magazine. She is Metalder's first human friend and constant companion.

Hakko Kita
A Grand Prix motorcyclist who was originally head of a motorcycle gang. He first appears in episode 16, where he meets Ryusei and Mai on a photo shoot for a new motorcycle magazine, and gets involved in the fighting. Calling himself the 'Neros Hunter', Kita saw himself as Mai's bodyguard and has feelings for her. Though Kita was willing to aide Ryusei's war against the Neros Empire, his efforts almost always result in a comedic or humiliating defeat.

Violent Spirit Top Gunder
A soldier who initially serves the Robotic Warrior Army. Top Gunder is a lone gunman in black tights and a single red-eye who believes in fair play. Though he originally intended to kill Metalder in a one-on-one fight, Top Gunder later gained respect for Metalder and became close allies with him. In Episode 33, a fake robotic Top Gunder was created to bait Metalder into a rescue, as the real Top Gunder had been captured by the armies of God Neros. The fake robot attacked Metalder shortly after being rescued, only to be shot and destroyed by the real Top Gunder when Crosslander exposed the deception. Also, in Episode 33, Top Gunder revealed that he, like Zargen, was capable of dreaming. He helped Metalder to bring down the Ghost Bank in Episodes 35-37, only to be killed by God Neros, who was in Coolgin's old armor.

Dr. Ryuichiro Koga
A leading authority in Robotic Engineering and the man who created Metalder. After World War II, Dr. Koga went to America and became a staff member at NASA. He returned to Japan when he learned of the existence of the Neros Empire and its ties to his past actions, prompting him to activate Metalder. Battered from Strobe's attempt on his life, Koga makes it to the base and activates the android from his rest. Soon after, in order to give Ryusei a sense of purpose, Koga allows himself to be killed by Chuubo and the Neros Empire members at the end of the first episode.

2nd Sub-lieutenant Tatsuo Koga
Dr. Koga's only son, whom Metalder was modeled after. He died in October 1944 as the first member of the Kamikaze Special Attack Squads. He loved music and played the violin with the potential to be a great violinist.

Shingo Ogi
Mai's father, who lives in Washington DC as a news reporter. As a favor to Mai, he investigates Dr. Koga's past and learns about God Neros' identity. In Episode 35, he is abducted by the Secretaries and taken to the Ghostbank. In Episode 36, he is brainwashed by God Neros and forced to wear the armor of the late Tagsky to battle Metalder. Shingo becomes free from the brainwashing when Metalder strikes him with his Laser Arm.