Rei is a girl with a fiery
personality. She was discovered when Jadeite kidnapped
lot of people near the Hikawa Temple, where she lived.
She's a Shinto Priestess in her grandfather's temple. Her
parents aren't mentioned in the Anime, but in the manga
it's explained that her mother died and her father is a
politician. She dreams of being lots of things, model,
singer, songwriter and lot of stuff more.
Rei is always arguing with Usagi, though she's really the most protective to her of the Senshi. It maybe deals with the fact that first Rei followed Mamoru thinking he was her boyfriend. Later on, Mamoru and Usagi discovered they were in love in their past life and Rei turned back. Also she gets mad with Usagi for being so clumsy and ditzy. There is another guy in Rei's life; he is Yuuichirou Kumada, who lives in the temple. She doesn't admit it but she likes him, and he is worthy to die for her. She even has kissed him several times.
Her name means Spirit/Beauty of Fire. As her name says, her powers are fire based. This is explained when you see that the Japanese call Mars by Fire Star. In SuperS she transforms in Super Sailor Mars.