Gradius​ is a horizontally-scrolling shoot 'em up produced by Konami originally released as a coin-operated arcade game in 1985. It was the first game in the Gradius series of shoot 'em ups. In Gradius, the player must maneuver a spacecraft known as the Vic Viper that must defend itself from the various alien enemies. The game featured a power-up system in which a weapon selection meter called the "power meter", based upon collecting capsules to 'purchase' additional weapon

The player controls the trans-dimensional spaceship Vic Viper, and must battle waves of enemies through various different environments. When gameplay begins, the Vic Viper is relatively slow and has only a weak gun. This level of capability is generally insufficient for engaging enemies, but the Vic Viper can gain greater capabilities by collecting and using power-up items.

While most arcade games utilize distinct power up-items that each correspond to a specific effect on the player character, Gradius has a single power-up item. The effect of this power-up item is to advance the currently selected item in a power-up menu that appears at the bottom of the screen. When the desired power-up is highlighted, the player can obtain it by pressing the power-up button, returning the menu to its initial state in which no power-up is highlighted.