Our protagonist Hiro created Team BRIGHT along with his friends when they were in elementary school. The team attracted much attention, especially armament specialist Sota, but their Gunpla (the 78) disappeared on the day before the tournament, leading them to quarrel and split up. Now, four years later, the former group record-keeper Imaizumi sends the other members a video and they meet at their old school. However, Imaizumi isn't there, and Hiro and his friends find something else instead...

Hiro's and Sota's hearts burn bright again when they play together in their first Gunpla Battle since their elementary-school days. They visit their old secret base to reunite Team BRIGHT and prepare for the National Tournament. Problematically, Nakamaru has been letting his female classmates use the base, and they have to share the space now. Sota worries that the girls will hinder the team's activities, but Hiro is excited to have them there. Meanwhile, a strong team named MONSTRE requests a match.

Team BRIGHT meets with Sendo, a once-famous legendary craftsman. They ask Sendo to build an original weapon for the team. As Hiro struggles to understand why Sota left the team, he encourages them to come up with a strategy for their next battle. The girls' conversation at the base leads Kentaro to suggest using psychological warfare. On the day of the match, their commander, Nakamura, comes up with a plan to lower the other team's guard.

Shiraboshi tries to recruit Takumi to join MONSTRE. Hiro's suspicion towards Takumi grows when he delays responding to the invitation. Takumi's pent-up frustration at Hiro explodes because Hiro has not grown out of his elementary-school mentality, and they have a huge fight. The next day, Hiro does not answer Takumi's call. Takumi knocks on the door of MONSTRE's base...

After team BRIGHT battles Sendo to a draw, they conclude that they couldn't win because of the difference in armament skills. Takumi feels responsible for not being able to fill Sota's shoes. Meanwhile, Kentaro thinks of ""the paint's ingredients"" while watching Satsuki, Mana, and Momoka recording a makeup video. They analyze the Gunplasky particle adhesion rate on their Gunpla (the 78) , which affects the mobile suit's performance, and learn...