Nils Nielsen invites Sei Iori, Meijin Kawaguchi, and others to an exhibition combat utilizing the new large-scale battle system he has devised the day before the Yajima Stadium's completion ceremony. Now that they've all been reunited, Sei tries to show off the Build Strike Cosmos that he's updated for the display, but he finds something is missing... Meanwhile, someone takes over the stadium's systems, trapping Sei and the others within. A strange gang emerges in front of them, challenging them to a Gunpla Battle.