During the second period of the World Tournament, all the players must compete in a Battle Royal elimination match. In the middle of the fighting, the battle is interrupted by the sudden appearance of a giant Mega Size Gunpla which belongs to none of the participating players. The other Gunpla have no way to deal with its overwhelming firepower, and since it isn’t related to the tournament, most of the players try to avoid fighting it. But Reiji, on the other hand, boldly challenges the giant Gunpla. His seemingly reckless fighting spirit is backed up by the Star Build Strike, the new Gunpla that Sei has built. To win the fight, Sei activates the Discharge System installed in the Star Build Strike.