When the sinister Carat Diamond and his scientific partner Dr. Mook organize an elaborate robot tournament in the distant Diamond City, they set their sights on capturing BomberMan himself to harness his combat prowess. Their scheme begins with an imposter sent to Peace Town to abduct the genuine hero, but Black BomberMan intercepts the plot—only to fall victim to Diamond's mechanical forces and lose his stronghold in the process. Escaping to seek aid from White BomberMan, the defeated warrior reveals the full extent of the threat: an advancing army of hostile robots marching toward Peace Town. With their homeland under siege and time running short, the two heroes must unite against Diamond's overwhelming forces to save their world from conquest.