You thought the world would be free of radioactive threats from the underworld after the events of the original Blaster Master, but for unknown reasons, several radioactive foci are sprouting from the ground all over the world. Once again you must get into your armor and travel to underground caves in order to discover the truth behind the new threat.
Blaster Master Jr. is somewhat of a direct sequel to Blaster Master, your mission is to control your character through a series of top-down underground dungeons and defeat the enemies you encounter there. You no longer have your trusty tank to take with you in scrolling zones, nor grenades, but to help you in the dungeons you now have the ability to have special bombs that can be used to kill enemies, as well as clear paths through the dungeons a la bomber of the king.