Due to a chance encounter with an actual space pilot. Nono, finds herself becoming part of the elite Fraternity. Made up of teenage pilots called Topless, and armed with quasi-humanoid weapons called Buster Machines, the Fraternity’s mission is to protect the people of the Solar System from attack by swarms of space monsters.

The story revolves around Taiga, who doesn’t have memories from further back than two years ago when his parents died in an accident. He lives with his sister, Tsubame, whom he finds out is from outer space with the job of protecting him as he possesses the Origin Heart.