Rea Masaki is a supporting character in Tenchi Muyo! Ryo-Ohki!, appearing for the first time in OVA 3. She is the current wife of Nobuyuki Masaki, stepmother of Tenchi Masaki and mother of Kenshi Masaki.
As revealed in the Tenchi Ban 13.8, Rea was an artifical human from Geminar, who was found by Kiyone Masaki and adopted into the Masaki family. She eventually became a friend of the family and Nobuyuki's assistant at his architecture office. She had been taught cooking by Kiyone, so even though she does have her favorite recipes, her cooking style is identical to Kiyone's.On the day of Kiyone's funeral rites, she was checking on young Tenchi when she noticed the boy had disappeared. Everyone present searched around for Tenchi but couldn't find him. It was during this search that Rea thought of something. Taking Nobuyuki with her, they found Tenchi asleep at the entrance to the cave where space pirate Ryoko was imprisoned. Tenchi was forbidden to go to the cave by his grandfather Katsuhito, but always went there anyway.
Rea would end up cooking and cleaning house for the Masakis. Sometime after Ryoko was released, she would move in with Nobuyuki at an apartment near the site of the house that Nobuyuki designed during Kiyone's lifetime (that house had been moved near the family shrine, destroyed when Mihoshi crashed into it, and rebuilt at the same site). When the school which Tenchi attended was destroyed by fire (in actuality it was Ryoko's doing), not to mention the Great Seto Bridge's destruction, she and Katsuhito were called to Tokyo to explain what had happened, at the Japanese Imperial Palace no less. At the last minute, Katsuhito made Rea make the report herself. Months later, she revealed this fact to Tenchi when he came over for a visit, but when he asked her why, she said he would be told about it later.
Later, when Tenchi discovered his mother's true personality of being a huge prankster, he became upset because the mother he remembered was nothing like that. Rea tells him that she feels sorry for his mother because the one he remembers is not Kiyone. Tenchi realizes that he had mixed his memories of his mother with memories of Rea, being that she took over the motherly role after Kiyone's death.Rea married Nobuyuki in the final episode of OVA 3, and in the spinoff, Tenchi Muyo! GXP, nearly a year later, it is shown that she is pregnant.
The 2nd spinoff, Tenchi Muyo! War on Geminar, centers around her son Kenshi. In OAV Episode 12, Kenshi is revealed to be the descendant of an artifical human and a human, making Rea a possible artificial human, or descendant of an artificial human from alternate world, Geminar, where Kenshi has been transported to.