Space Sheriff Shaider: The Movie

It's the film adaptation of the Metal Heroes series of the same name. This movie takes place between episodes 19 and 20. An alien assassin who makes a living by hunting down Space Sheriffs, arrives on Earth, adapting a helmet, twin shoulder cannons, and other weapons into his fighting style after losing to Gavan and Sharivan, Omega targeted Shaider and challenges him to fight to death. However, Hessler and the Girls' Army intervene out of pride by holding Annie and the children hostage, Omega stops them from killing Shaider. Soon after saving the children, Shaider battles Omega with Annie and the Fuuma as witnesses as Omega finally falls to Shaider's Shaider Blue Flash.
(Source: kamenrider.wikia)