One

Kay lives a normal, seemingly perfect life. Well, that is, until aliens invade. In this world, the idea of aliens was cast out by religion. The aliens are called Crusades, as their main objective is to take inhabitants of planets and build armies, and capture planets. Meanwhile, they bring the Blue Plague with them. In this plague, red flakes appear in your eyes, you cough blood, a blue mark appears on your chest, then over time you system slowly shuts down, usually you spend six months in misery. Kay, however, is immune. Her sister catches the mysterious plague, and her best friend is taken and gets a wrist harness, an eel like creature that wraps around you wrist and controls you, and becomes high in the ranks of the Crusades. How will Kay survive, save her sister, and stay sane?