As a child, Yuuma fought a Gunpla Battle with his Gundam Airmaster and was destroyed by an opponent who mocked his skills and said he had no talent. At school, Yuuma thinks about the Build Burning and wonders what Sekai was doing with it. The teacher introduces Sekai as a new transfer student, and he weirds out the class by talking about martial arts and the Gunpla Battle Club. Sekai sits down next to Yuuma and says he wants to fight again, but Yuuma tells him that he doesn’t play Gunpla Battle anymore. Yuuma sees Fumina outside in PE class and she waves at him, but he ignores her. At lunchtime, Fumina visits Sekai and tells him they should discuss their plans. Sekai freaks out when he can’t find his lunch, but Mirai walks in and delivers it to him. Several boys become jealous that Sekai has Mirai for a sister and Fumina for a friend. Sekai falls asleep outside while Fumina and Mirai eat lunch. Fumina promises to look after Sekai, but Mirai thinks that’ll be a challenge since he’s crude, careless, simple-minded, hot-headed, gluttonous and disorganized. Despite all that, Fumina thinks that he’s straightforward, even though they just met. Miyaga tells Plamo Club Vice President Eri Shinoda that he has no choice and asks Yuuma for a favor. Fumina introduces Sekai to Ral, who serves as the club’s special coach. Ral starts quoting Ramba Ral’s dialogue from Gundam until Fumina tells him to stop. Fumina explains to Sekai that they’re the only members because the last few were scooped up by the Plamo Club. She notes that Sekai fought its president, and the two joke about Miyaga looking like a preying mantis. Miyaga walks in on the insult and brings the student council president over, who announces that the Gunpla Battle Club will be folded into the Plamo Club. Ral asks what can be done, and the president answers that the club has to demonstrate its usefulness in a three-on-three battle tomorrow. Fumina objects to the short deadline, and Miyaga tells her that if she doesn’t find someone, they’ll have to fight two-on-three. Miyaga introduces his team, which includes Eri and Yuuma. At home, Fumina recalls Yuuma telling her that he was quitting Gunpla Battle despite their promise to enter the championship together. Sekai talks to Mirai about the situation, and Mirai suggests that it’s Sekai’s turn to find out why Yuuma won’t explain things to Fumina.
The next day, Fumina and Sekai show up with no other members, which she blames Miyaga for. Miyaga asks if he looks like an underhanded guy, and Fumina immediately answers that he does. The battle begins in a canyon level and Fumina launches in her Powered GM Cardigan, followed by Sekai in the Build Burning. Miyaga launches in his Enact, followed by Eri in a Hobby Hizack and Yuuma in the Lightning Gundam. Fumina asks Sekai to hide with her inside the canyon wall and warns him not to go out because Yuuma specializes in sniping. When they don’t take the bait, Eri tries to draw them out by flying in the open air, which gets her shot down by Fumina. Fumina thinks the odds are even now, but the joy is short-lived when Yuuma snipes her rifle due to Fumina revealing her position. Miyaga takes to the air and fires on the canyon to rain rocks down on Fumina and force her out. Yuuma hesitates in sniping her, which allows Sekai to attack at close range with a kick. Without Yuuma’s support, Miyaga has trouble fighting Fumina. Sekai knows that Yuuma can’t use his rifle and asks him why he’s blocking Fumina’s dream. Sekai uses a Jigen Haoh punch and says that Yuuma really does want to play Gunpla Battle, but he’s cowardly and ran away. Yuuma yells that Sekai doesn’t know him, but Sekai counters that he can hear Yuuma’s loud roar through his fist. The battlefield starts to vibrate when Miyaga brings in the mobile armor Agrissa and docks with it. Fumina notes that bringing in a mobile armor is against championship rules, but Miyaga reminds her that this isn’t a championship fight. Miyaga uses the Agrissa’s power to electrocute the Powered GM Cardigan and cause heavy damage. He then creepily offers to show Fumina his plamo techniques. Fumina vows that she won’t give up her dream and will keep her promise, which causes Yuuma to remember promising to fight together as children. Following his crushing defeat, Yuuma told his older sister China that he’d have to break his promise to Fumina and quit battling. China told him that even without the promise, Fumina would still want to play Gunpla Battle with him. Yuuma fires his rifle at the Agrissa and tells Miyaga that he violated the rules and created an unfair fight. Sekai then rushes in and uses a Seiso-Geri kick to damage the Agrissa, which Fumina then destroys with her machine guns. Miyaga then tries to grab her, but Yuuma snipes the Enact and destroys it. With the battle over, the council president decides to leave the club be. Eri vows to stay by Miyaga’s side, so Fumina wonders if she lost deliberately. Later, Yuuma wonders if he can do it and vows that he will fight and keep his promise to Fumina. The next day, Fumina and Sekai try to get Yuuma to join the club, and he gives in when he meets Mirai and sees how attractive she is.
The Gunpla Battle Club fights for its existence against the creepy machinations of Miyaga. He thinks he’s come up with a clever strategy to get his hands on Fumina (in more ways than one), and it relies on her fractured friendship with Yuuma. At some point, young Yuuma was beaten so badly by some jerky guy that he decided to quit Gunpla Battle entirely. I guess he’s not a very good loser if one single loss convinces him to give up something he enjoys. And because of that loss, he and Fumina haven’t been good friends anymore, which is rather silly. Then again, they are middle schoolers. China makes a flashback cameo, and Ral is established as a special coach, which at least gives him a better reason to hang around the school. Sekai sounds even more like Domon Kasshu with his talk of understanding things through his fists. There is clearly some secret to the Build Burning since Yuuma is familiar with it, so I’m sure that’ll be addressed at some point. The question now is, can these three kids with such different personalities and fighting styles effectively work together as a team? Eventually, sure, but I’m guessing it’ll be a rough road full of comedic mishaps.