Nono, a country girl chasing her dream of becoming a space pilot, joins the elite Fraternity, a defense force built around teenage pilots called Topless, who each command a giant mecha known as a Buster Machine. She idolizes ace pilot Lal'C Melk Mark from the moment they meet, and works to prove herself worthy of flying alongside her as the Fraternity holds the line against invading space monsters. This manga adapts the Diebuster OVA, the sequel to the original Gunbuster.