The story is set in the near future when GunPla Battles, competitions that pit Gundam plastic models against each other, have become popular worldwide in the "Second GunPla Boom." Sei Iori, a first-year middle-school student and the only son of a model shop owner, is talented at building GunPla, but inexperienced in the GunPla Battles. He encounters a mysterious boy named Reiji, who happens to be an accomplished Gundam Fighter. Together, they strive for the GunPla Battle world championships.