A young girl leaves her home on Mars with a dream to be a space pilot. Once in the capital, Nono meets top pilot Lal'C during a space monster attack, and joins the Solar Defense Force. Shockingly, Nono is revealed to be an android, thus unable to achieve elite Topless status and is stuck as Lal'C's largely-ignored trainee. Nono then decides the best way to advance is by recovering a lost Buster mech for herself to operate like the Topless do. She receives such an assignment and heads to Pluto. Meanwhile on Titan, the SDF unearths an ancient alien “Eternal“ Topless, which results in to a large space monster invasion. Coincidentally, the humans notice Nono's android presence also attracts monsters, and half the alien fleet gets diverted to Pluto to battle Nono in her new Buster form. Events escalate and the surviving SDF takes the offensive towards the 11th planet, the space monster homeworld.