Grandpa "Ojii-san" Hino
Rei's grandfather runs the Shinto shrine "Hikawa Jinja". He took Rei in because her mother passed away and her father was a very busy business man who had little time to watch over his daughter.
He and Rei get in major fights all the time. When they do get in fights it's almost always about Rei not doing her chores and such. Both being very stubborn people, they hardly ever get along. When they do get along, Grandpa Hino is seen as a very happy and energetic guy.
In the SailormoonR Grandpa Hino is VERY desperate to find a helper. He is preferring girls, because he's a pervert. Most girls wont do it because they're scared of him or they're not intersted. I wonder why they're scared... A couple of episodes later we see that he hires Yuuichirou, and Grandpa Hino trains Yuuichirou to be a great fighter, and a great Temple master. Rei is very fond of Yuuichirou, but she never admits it.
Rei's grandfather was also a keeper of a Rainbow Crystal in the first season of Sailormoon. He showed a lot of nerve, and power to Zoisite because he was able to get away. After a few struggles, his Rainbow Crystal was taken and he changed into a gorilla Youma. When he changed over he tried to kill the senshi. Rei learns of the Youma's true identity and begs Sailormoon to save him. Sailormoon uses "Moon Healing Escalation", and saves Grandpa Hino.
In the first season Grandpa Hino was seen in almost every episode but as every season passed, he was slowly faded out. He was not seen at all in SuperS and Stars.