Kamen Rider Black: Hurry to Demon Island! (1988)

Originally known simply as Kamen Rider Black during its theatrical release. Children all over Tokyo mysteriously disappear without warning. Kotaro suspects that the Gorgom are behind the abductions and follows a suspicious-looking tour bus with children on it, only to lose its trail off a cliff. With the help of a fisherman, Kotaro travels to a remote island and uses his abilities as Kamen Rider Black to save the children and foil Gorgom's latest evil scheme.