Sei Iori is a Gunpla builder whose family runs a hobby shop in a small town. He aspires to be a Gunpla Battle champion like his father, but despite his exceptional building skills, he lacks the combat abilities to compete with other contestants. Then one day, he meets a mysterious boy named Reiji, who helps him improve his confidence in participating in Gunpla Battles. Together, Sei and Reiji battle their way to the 7th Gunpla Battle World Tournament.
Seven years have passed since Sei Iori won the 7th Gunpla Battle Championship World Tournament. The Gunpla Battle Championship is now run by Yajima Trading. With new rules and new battle modes, the game's popularity has become even more widespread.
However, the Seiho Academy that Sei Iori once attended has failed to catch onto the trend. The only member of the school's Gunpla Battle Club is its president, middle schooler Fumina Hoshino. Currently, there is no way the club can participate in the middle and high-school division of the upcoming All-Japan Gunpla Battle Championship, where players fight in teams of three.
Then Fumina meets a new transfer student. He is Sekai Kamiki, a young martial artist who has been traveling with his master. Together with a young Gunpla builder named Yuuma Kousaka, they finally have three members for their team.