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.

Kaito and Akiho go with their teacher, Mitsuhiko Nagafukada, to where the Robo-One tournament is being held, though they have no hotel to check into. As Kaito practises with the robot, he experiences a strange sensation for a brief moment. The tournament soon begins and Kaito manages to use his tactics to get through the preliminaries and into the finals. Before the final match, Akiho starts to grow concerned about Kaito, who hadn't gotten a lot of sleep prior to the tournament. The final match soon begins against the reigning champion, Mr. Pleiades, whose robot has some fierce tricks up its sleeve. While Kaito's robot is at a disadvantage against Subaru's, Kaito suddenly experiences an inverse of the ailment Akiho has, slowing down time for him, and makes a counterattack, knocking both of them out, though this technically results in Kaito's loss. Upon returning home, Kaito has a brief encounter with Kill Ballad's creator, Frau Koujirou.

As the robots continue to run rampant in Tokyo, Kona explains to Kaito that the login to their control panel has been altered by the hackers to require they defeat a Kill-Ballad CPU opponent. Struggling to beat the opponent, Kaito decides to try and force his slow-mo by pushing his body to its limits, but to no avail. Kona soon founds out the person behind the hack was one of the members from her development circle, Maguyan, who claims he was forced to do it as his family was taken hostage. Kaito soon realises that Maguyan has in fact been brainwashed. As Kona hears the support of her friends from the Robotics Club, she explains how she created Kill-Ballad to keep Gunvarrel, and her mother's memories, alive. As the police show at Kona's doorstep, Akiho, Junna and Subaru help lure them away, buying Kaito and Kona some time to beat the Kill-Ballad opponent.

The gang complete the construction of the GunPro-2, using the monopole motors and a laser-activated fuelling system, and successfully put it through its first activation test. Shortly afterwards, though, Nae informs the group that they will be unable to use JAXA for a week as there are plans to launch a rocket. Whilst Kaito goes off to search for Kikijima's next report, the others run more tests on the GunPro-2, where Junna notices something odd about its walk cycle. As Subaru runs alongside it to figure out what is wrong, a sudden gust of wind sends the robot toppling towards him. Meanwhile, as Kaito finds the location of the seventh report, Mizuka confronts him, warning him not to pursue the reports. Just then, Kagome Kagome once again plays on their Pokecoms and a strange noise plays upon Mizuka answering it, causing her robotic legs to go out of control and work her towards a cliff edge.

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.