Rei lives with her grandfather and a formerly homeless man named Yuuichirou at the Hikawa Jinja, a Shinto temple. Her mother died when she was young, and her father, being a famous politician, was too busy to take care of her. She attends a Catholic school, however; T*A Private Girls' School. She is a miko (shrine maiden) at the temple, under the instruction of her grandfather, and has many duties to perform and powers related to her Shinto background. Most kids she knew considered her "weird" and "spooky" for this. When Usagi met her, however, she thought Rei seemed kinda cool, and when she found out she was Mars, they became friends... even though it doesn't show a lot of the time.
In both the anime and the manga, Rei keeps separate from most people. She is dedicated to her duties as a miko and uses her powers to assist the Senshi in their battles. She wants to be an idol singer someday.
In the anime, Rei has a quick temper and is cruel to Usagi even though she's her best friend. She also treats Yuuichirou badly even though she has a crush on him. She argues with her grandfather a lot. It seems like she treats those she cares for most the worst ^^;;
In the manga, Rei is very mature and treats everyone well. She seems to be best friends with Minako. She has two pet crows, Phobos and Deimos, who can turn into humans, and are also Senshi. They are named after moons of Mars. There is no Yuuichirou. She says that she "has no interest in men" [ note: as in having a relationship ^^;; ]
Rei has long black hair in the anime, but it's purple in the manga, sometimes appearing dark blue or black. Her eyes are dark purple. She sometimes wears earrings. She's about average height. When she isn't in her miko robes or school uniform, she wears normal teenager clothes.
As Mars, her powers are based on fire; her weapon is a bow and arrow made of fire. Her fuku is red with a purple bow, the back bow also being red. Her shoes are red highheels, and she has dangling red stars for earrings. She has a thick stripe on her collar.
When I first saw the DiC version, I hated her! But she grew on me after awhile :) Then I saw the Japanese version, and she blew me away! She's really cool! I wish she was a bit nicer to Usagi, but you have to admit, some of their arguments are hilarious! And she's great in the manga, too. She's really pretty, and I love her powers ("Fire! Fire!"... j/k, but they are cool.)