In the midst of escalating conflicts between the Federation and the rebel Crossbones Vanguard, young Seabook Arno finds himself entangled in the chaos as his hometown becomes a battleground. Amidst the political upheaval, Seabook encounters Cecily Fairchild, the granddaughter of aristocrat Meitzer Ronah, who aims to forge a new order known as 'Cosmo Babylonia.' Backed by the Crossbone Vanguard, the Ronah family's ambition threatens to reshape society in favor of the elite, leaving the common folk in dire straits. Entrusted with piloting the Gundam F91, a mobile suit designed by his mother, Seabook faces a crucial decision: uphold the Federation's regime or join forces with Cecily to envision a more equitable future for all.