Back in the '80s, the success of the series Mobile Suit Gundam lead the massive Gunpla Boom on which drive the sales of Gunpla, Plastic Models that were bought by collectors to staggering good heights. Years later in the future, with the success of the second Gunpla Boom, special tournaments called Gunpla Battles were established throughout the world to see which customized Gunpla and its builder is the best. These incredibly-popular Battles culminate in a yearly global tournament.

The story revolves around Sei Iori, a young Gunpla Builder and student who has a dream on becoming the best Gunpla Fighter in the tournament and someday became as good as his father. As the only child, his family owns a small Gunpla Shop and his talent is well-honed, however his weak piloting abilities have led him to a series of first-round losses. But one day, he met a strange boy named Reiji and helped him out. Reiji gave him a jewel on which he will come to Sei's aid if he wished enough. Together, both of them will tackle the world of Gunpla Battle and compete in the tournament using Sei's customized Gunpla, the GAT-X105B Build Strike Gundam.