Gun Frontier is a 1990 arcade vertical shoot-'em-up developed by Taito. Taking place on the planet gloria, a newly colonised planet with a manner of living similar to that of the american west, the player fights to defend settlers from airborne pirates, many of which are shaped after guns of the old west. Guns and bombs are levelled-up and collected by dropped power-ups, which are money-themed, with the gun upgrades shown as American dimes and bombs as gold bars.

The year is 2120: Earthlings have spread beyond their galaxy and have started to colonize uninhabited planets in different solar systems. One such planet to be colonized was the Earth-like planet Gloria which happened to have an enormous natural supply of gold. This discovery became pivotal to Gloria's emigration, so much that emigrators would be impoverished by the cost of reaching the planet. Because of this, life on the planet thrived in a setting similar to the American Old West. Though poor, the gold trade aided the Glorians in advancing technology and knowledge, so much that among the inhabitants lived talented inventors and engineers.

However, the Glorians were not the only ones who were tempted by the planet's gold: Space pirates known as the Wild Lizards quickly invade Gloria and decimate the towns of the people and enslave those who survived in an attempt to deplete the planet's gold supply.

Two inventors of Gloria who were a part of the planet's development teams decide to strike back at their invaders using two fighter planes in the shape of giant revolvers with plane wings.