Since I intend to use the same character as from Oblivion, she is a wandering merchant/historian who suffers from periodic blackouts in which she goes insane and attacks the people nearby. She spends most of her time wandering so that this doesn't happen, but during one of her brief respites in a town, blacks out and kills someone.
During her confinement, she finds Akatosh and considers the main quest to be her atonement for whatever sins she has commited and her unfortunate malady of random killing to be a blessing and a curse from Akatosh to enable her to carry out his will.