Battle Unit Zeoth is a 2D futuristic side-scrolling shooter. Humanity is in danger - a race of alien robots known as the "Grein" invaded the Solar System. They lost and fled, but left behind an underground base with self-replicating Grein machines. Two years after the invasion aliens attack again. However, the humans have made a special mech, Zeoth, designed for combat.

Player controls Zeoth who can move to the right and shoot enemies. The odd-numbered stages are horizontal scrolling stages and the even-numbered stages are a simple "platform" stages. Each stage ends in a boss fight. Zeoth can fly with a jetpack (but the player must tap a button to resist gravity) and can fire in four directions (right, left, down and up). The basic weapons can be improved. The mech can take some damage before being destroyed and has just one life, however, there are unlimited continues.