Gunvarrel is a prominent in-universe robot in the Robotics;Notes titles, originating from the in-universe anime Kidou Battler Gunvarrel. In Robotics;Notes, it is the Robotics Club's main goal to create a full-scale functional reproduction of the robot in real life.
Gunvarrel's first in-universe appearance was in Kidou Battler Gunvarrel, a massively popular anime that attained worldwide acclaim during its airtime. In the show, the giant robot is piloted by main character Genki Dotou.
For several years after the anime began airing, Central Tanegashima High's Robotics Club passed down the goal to produce a functioning, full-scale replica of the giant robot, which they entitled GunBuild. During the setting of Robotics;Notes, however, this effort is on its last legs; the only club members remaining are main characters Kaito Yashio and Akiho Senomiya, and of them, only Akiho is truly interested in doing the impossible and completing the project before they graduate. Yet, even with no end in sight, Akiho presses on, dragging an unwilling Kaito along the way. Over the course of the story, the two continue to work on building the robot, recruiting new club members as the story progresses to help out. Slowly but surely, the Robotics Club works to make their dream a reality.
In order to make the impossible possible, the club eventually enlists in the help of JAXA (based on the real life agency of the same name) to help build the Gunvarrel reproduction.The club eventually concedes that maintaining the actual proportions of the robot would be nigh-impossible if it were to theoretically function as well. With this in mind, the robot continues to be developed with a blocky, almost unsightly form—to mitigate this, however, the club employs the use of A.R. technology to allow the robot to maintain its popular appearance to an extent. Any person viewing the robot through their PhoneDroid via the IRUO. App would be able to see the robot in its futuristic form, as meant to be seen.