The story of Gundam F91 revolves around teenage space colonist Seabook Arno, his girlfriend Cecily Fairchild, and the efforts of the Crossbone Vanguard militia, led by Cecily's grandfather Meitzer Ronah, to establish an aristocracy known as "Cosmo Babylonia". In keeping with Gundam tradition, the civilian Seabook is forced by circumstance to pilot the F91 Gundam F91, coincidentally designed in part by his estranged mother, Dr. Monica Arno.