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.

Kaito arrives before Misaki, with the others helping to divert the missiles she fires using AR decoys, although Kaito is forced to use the Slow-Mo and sacrifice one of his pile bunkers to dodge the last one. Kaito manages to get up close to Misaki's Sumeragi and use the Slow-Mo to attack her with the other pile bunker. However, this knocks Misaki out and allows Kimijima to take full control of her as he divides the Sumeragi into a more mobile unit. After locking down the launch sequence, despite Nao and the other adults reclaming the control room, Kimijima launches an attack at the others forcing them to seperate, which leaves the Super Gunbuild-1 with only five minutes of power. Just then, Kona receives a program from Sawada that will erase Kimijima if they can get his avatar in the PokeCom's view, although it requires a reboot which leaves Kaito vulnerable.