Io is an Attendant of the Successor of Blood. The Successor she is assigned to is the protagonist player character of the game Code Vein. Io was created to serve this being eternally. However, Io began to question her role as Attendant and the meaning of her own life, soon thereafter seeking out the truth of her existence with the help of the protagonist. Will she continue to care for the Successor of Blood through her own free will, will she remain a puppet, or will she go on her own journey?