You are Kerotan, a frog who works for Cat & Frog, a teleporter company. But lately your boss seems to be very stressed — a strange plague of black monsters seems to be infecting the company's equipment, and it is your job to fix them.
Kero Blaster is a 2D platform video game with guns. You can shoot left, right or up and you have a selection of weapons which can be upgraded at a few shops sprinkled around the levels. You can also buy extra health and lives at such shops. The currency consists of coins which are dropped by killed enemies.
The main game has about half a dozen areas, each consisting of many screens. Lose a life, and you have to restart the screen; if you lose all your lives, you must restart the whole area. However, you always keep your coins, equipment and upgrades, even if you die.