There are many differences between the anime and manga version of this character. In the manga Rei never gets into those childish fights with me. She never dates Mamoru in the manga. In fact, in the manga Rei feels that men cannot be trusted. The only time Rei has a hint of romance is in Volume 11 "Casablanca Memory", with Kaidou-san, a friend of her father's.

More about Rei's family is told in the manga. It is revealed that her father is a politician and her mother died when she was young. She blamed her father and went to stay with her grandfather at his shrine

Overall, Rei has a more calmer personality in the manga. You never see her lose her temper a like in the anime. Also her friendship with Minako is more emphazied in the manga