Family.

Mother (Risa Hino)
Rei's mother is an enigmatic figure only mentioned very briefly. She is given the name 'Risa Hino' in the live action version of Sailor Moon, but not in any other version. It is noted that Rei looks like her mother, in the manga side story Casablanca Memories. Risa died when Rei was very young, Rei's father was not there for Risa when she died.

Father (Takashi Hino)
Rei's father is described as a famous politician (part of the fictional Democratic Liberal Party), who never really had time for his family. Rei deeply resents him, and says that she hates him. He is only given a name in the live action version of Sailor Moon, and in all others is simply called 'Rei's Father'. Takashi was not with his wife, Rei's mother, when she died which increased her loathing for him. While he does not necessarily attend her birthday every year, he does send her a gift of white Casablancas and a white dress, Rei knows that it is not him that picks out this gift and that it is his assistant Kaidou who does. In the live action version of Sailor Moon he hates Rei's powers, but visits her once a month to keep up his appearances with the media.

Cousin (Kengo Ibuki)
Rei's cousin is an anime only character. He appears exclusively in the episode 'The Scream of Dead Souls? Terror of a Monster at Camp'. He worked as a potter but was prone to fits of rage where he destroyed all of his work. He eventually has his Star Seed taken by Sailor Aluminum Seiren, and goes on a campsite destroying rampage. He is eventually stopped by Sailor Mars and Eternal Sailor Moon, and goes back to a peaceful life.

Grandfather
Rei's Grandfather appears in both the anime and the manga, though he features far more heavily in the former. Grandpa runs the shrine that Rei works at and hopes to take over one day. He is a notorious lecher in the anime. Despite his less than virtuous ways he is very protective of Rei, particularly from her anime-only love interest Yuuichirou Kumada. Another Anime only addition to Rei's Grandfather in the Anime is his use as Jiji one of the Seven Great Youma. In the manga, Grandpa has a smaller role, though he seems far more calm and sincere. He is one of the first to notice and appreciate Rei's gifts.