An evil alien empire known as the Bozon are launching a full-scale attack on Earth. As either Lt. Henry or Sgt. Sanders, the player must pilot a giant space mecha known as a "Mobilsuit" to defeat the aliens. Up to two players can play simultaneously. The controls of an eight-way joystick for moving the Mobilsuit and three action buttons. Side Arms uses two shooting button, one for shooting to the left and other to the right. The third button is used to change between the weapons acquired by the player. There are five types of power-ups that can be acquired by the player: a speed upgrade, an orbital bit that will provide additional firepower with the standard gun, a shotgun with shoots in a fan-shaped range, a 3-wayshooter, and a mega bazooka launcher that fires a laser beam. The player can choose what power-up their mecha will receive by shooting the power-up icon until getting the item they want. All of the weapons, as well as the mecha's speed, can be upgraded up to two or even three levels depending on the item. There's also a speed downgrade that will reduce the Mobilsuits speed by one level. There also two "Auto" power-ups as well shaped like the enemy characters from Vulgus: one is shaped like the "Yashichi" and allows the player to fire continuously with either firing button held down; while the other, which is shaped like the "Sakichi", allows the player to shoot upwards, downwards and forwards at the same time, but at a slower rate than the regular shot.