He is typically depicted as the rival of Kotaro Minami, aka Kamen Rider Black. Like Black, Shadow Moon utilizes the King Stone to transform into his Rider form and is armed with a sword, the Satan Saber.
Alongside his best friend and stepbrother, Kotaro Minami, Nobuhiko Akizuki was abducted by Gorgom to become one of their new Century Kings. Kotaro however, managed to escape after he was given a kingstone, allowing him to transform into Kamen Rider Black. In the process, Kotaro damaged Nobuhiko, forcing him into a deep slumber to recover from his wounds.
Nobuhiko later recovered from his wounds. Upon awakening he assumed leadership over Gorgom. He later went to go fight Kotaro. Shadow Moon attempted to fight his brainwashing and briefly turned back into Nobuhiko, but he was unable to keep fighting due to the Creation King's interference. With nothing to hold him back, Shadow Moon attacked Kotaro and ultimately killed him.
Shadow Moon later engaged in another duel with a revived Kotaro. Kamen Rider Black defeated him by using the Satan Saber to slash his Kingstone. He was last seen in the Gorgom Headquarters as it was exploding.
He returned during his step-brothers fight against the Crisis Empire. Wielding the twin Shadow Sabers he had claimed from the Crisis Empire, he sought revenge against Kotaro. He was finally killed when RX stabbed his Kingstone with the Revolcane. As he dies, he informs Kotaro of the Crisis Empire's plans to cause a volcano to erupt.
Kamen Rider Decade: All Riders Vs. Dai Shocker
Shadow Moon returns again, this time as Nobuhiko Tsukikage, a butler to the Kadoya family and an alternate reality version of Nobuhiko Azikuzi. While Tsukasa was away, he took care of Sayo Kadoya. When Tsukasa returns and reassumes leadership of Dai-Shocker, he usurps him and convinces Sayo to become High Priestess Bishium.
However, Decade later joined up with the other Kamen Riders and they all attacked the forces of Dai-Shocker. Nobuhiko transformed into Shadow Moon and fought Decade and Kuuga, but was defeated and slammed into the wall by Kamen Rider Double. He was then finished off by the Kamen Riders kicking him at the same time in an "All Rider Kick".
Kamen Rider x Super Sentai x Space Sheriff x Super Hero Taisen Z
Shadow Moon returns once again as one of the main antagonists of this movie alongside Space Reider. Here, he leads a new incarnation of Shocker called Space Shocker and is secretly working with Reider to capture Psycholon to revive Demon King Psycho. He is later defeated by the Kyoryugers.