Kaito Yashio and his friend Akiho Senomiya are the remaining members of their school's Robotics Club. After Akiho hands in a budget request to the staff room, both she and Kaito, who spends his time playing games on his PokeCon device, visit an old hangar containing a large robot the Robotics Club has been working on since its foundation, Gunvarrel, based on a popular robot anime whose final episode was never aired. The next day, the vice-principal agrees to give the Robotics Club their proposed budget on the condition that they win a robot tournament taking place in two week's time, with the club to be disbanded should they lose. As Kaito and Akiho contemplate if they can pull off such a feat, a mysterious girl is seen making a report.

After Kaito, Akiho and Mitsuhiko pay their respects to Mizuka, the vice-president announces that, following Subaru's accident, the Robotics Club will be disbanded and their cooperation with JAXA halted, ordering all the robots they've made to be dismantled. As Kaito, against his better judgement, goes to download the seventh report, he is confronted by Toshiyuki Sawada of Exoskeleton Inc., who questions him about Kimijima, though Kaito refuses to answer him. Afterwards, Kaito receives a call from Misaki, warning him not to show the reports to anyone. After having a nightmare about Misaki, Akiho tells Kaito that she intends to finish the robot and take it to the expo herself. Despite finding the notion ridiculous, Kaito agrees to hear her out if she beats him in Kill Ballad which, to her surprise, she manages to do. As such, Kaito agrees to help, with Doc and Mitsuhiko also providing their support.

Whilst everyone else works on fixing up the GunBuild-1, Kaito, Nae and Airi head to Kimijima's lab to retrieve data for the device Sawada gave him, although Kaito undergoes a seizure when he attempts to activate it. Just then, they are confronted by some armed droids run by Kimijima and Sister Centipede. However, Sister Centipede manages to have the droids shoot each other, only to be erased by Kimijima shortly afterwards. Meanwhile, as Akiho and the others complete the GunBuild-1, which she renames the Super GunBuild-1, she reunites with Ken'ichirō before learning of Kaito's condition. Despite his injuries, Kaito insists that he be Super GunBuild-1's operator, believing that the device Sawada gave him can trigger his Slow-Mo at will, giving him a chance against the Sumeragi. Akiho objects, however, believing using the device could kill him. Kaito assures her that he will help her meet Misa face-to-face again, giving her the Slow-Mo trigger.