An organization called "Amadeus" wants to take over all the military computers in the world using a new virus they have created. It's your mission to destroy them before they accomplish their evil ambition.
The 5th episode (including Metal Slug X) of the most famous arcade-shooting-series comes bringing the unaltered classic gameplay, a new arm (Dual Machine Gun), 6 new vehicles (Motorcycle, Truck, Bradley Tank, Metal Crow Tank, Four Legged Walkmachine and Forklift Truck) as well as 2 new soldiers for the pantheon (Nadia Cassel and Trevor Spacey).

The most notable introduction to the series is the Metalish System, giving to the player a new possibility to score more points: after pick up certain shield-shape emblems, a timer bar will be displayed at the top of the screen. During this time, you must to shoot rapidly as many enemies as possible and, depending on your acting, you will receive a corresponding badge bonus that will be added to your score after completing it. But, if you die during the mission, the bonus will be lost.