In the near future, GunPla Battles, competitions that pit Gundam plastic models against each other, have become popular worldwide in the Second GunPla Boom. Iori Sei, 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. Sei's customized GunPla is the Build Strike Gundam.