The main character of Plastic Little is Tita Mu Koshigaya, Tita to her friends, a young woman who captains a ship, the Cha-Cha Maru, whose business is capturing exotic creatures in the sea of clouds of the planet Ietta, apparently a gas giant of some kind, and selling them to collectors and zoos. By chance, she saves Elysse Aldo Mordish, a young woman of her own age, from a rogue faction of Ietta's own military forces, led by the armored commander Guizel, who already killed Elysse's scientist father. As the military conducts a vicious chase for Elysse, it becomes apparent that she holds the key to a secret that could determine the fate of the entire planet's independence.