This anime compilation movie takes the six episode Diebuster OVA series and reedits the material into a 95 minute theatrical movie. The story takes place after the events of the previous series/compilation film, Gunbuster, telling the story of a country girl named Nono, who dreams of becoming a star pilot in the elite squad of "Topless" fighters known as the Fraternity. Nono wants nothing more than to protect humanity from the terror of the space monsters, but before she can live out her fantasy, she'll have to learn to be less clumsy -- so her Buster Machine doesn't fry the galaxy.
In the very near future, a race of huge, insectoid aliens are discovered traveling the galaxy. These aliens, which are known as the Uchuu Kaijuu, or Space Monsters, seem dedicated to the eradication of the human species as the latter takes its first steps away from the solar system, and they are getting closer and closer to Earth. Humanity has responded by developing space-going battleships and giant fighting robots. These complex robots—RX-7 Machine Weapons—are actually an advanced type of fighting suit, piloted by a single occupant. As advanced as they are, however, they are being used as trainers for a new weapon, the Gunbuster. However, being relatively new technology, they are difficult to operate (stock shots show pilots working multiple controls with hands and feet, while fingers rapidly operate switches on the hand grips), so pilot candidates are selected from the best and brightest youth on Earth and the Lunar colony. These are trained at schools around the world.