Heavy Object unfolds in a distant future where war is dominated by "Objects"—massive, spherical tanks that are effectively invulnerable to standard weapons and armed with overwhelming firepower. On the battlefield, these machines decide the outcome of conflicts so completely that conventional armies have been reduced to support roles, and the old rules of war have all but disappeared.
The story follows Qwenthur Barbotage, a student studying Object Design, and Havia Winchell, a radar analyst of noble birth, as they serve in the Legitimate Kingdom's 37th Mobile Maintenance Battalion. Assigned to support the Baby Magnum, one of the nation's Objects, the two soldiers find themselves caught in a battle that goes badly wrong and leaves them face-to-face with the terrifying power of an enemy Object. Forced to survive with little more than their ingenuity and nerve, they begin to challenge the certainty that Objects always guarantee victory.
Alongside Milinda Brantini, the Baby Magnum's pilot, and their commanding officer Frolaytia Capistrano, Qwenthur and Havia travel across the globe from one crisis to the next. Each mission pushes the unit into another seemingly impossible confrontation, where wit, courage, and teamwork become the only weapons capable of standing against the insurmountable foes that are Objects.