About Shadow Moon:
Nobuhiko Akizuki - the stepbrother of Kotaro Minami who was also born in the same day during the eclipse. Kotaro and Nobuhiko essentially growing up together and forming something of a sibling relationship. On the night of their 19th birthday party, Kotaro and Nobuhiko were kidnapped by a criminal cult group, Gorgom, to implant the Kingstone in order to validate them as the candidates to succeed Gorgom Creation King. Unlike Kotaro, Nobuhiko unable to escape from the brainwash process during the cyborg surgery and being mind altered become the Shadow Moon. As a candidate of the Creation King successor, Shadow Moon and Masked Rider Black are required to fight in each other and whoever wins will become the next Creation King. Later in the series, Shadow Moon was defeated by Masked Rider Black. Shadow Moon spitefully told Kotaro to feel regret knowing that he had murdered his brother, Nobuhiko by being the victor of their fight before he dead.