Tennyo is an exact double for Kiyone Masaki, Tenchi's and her mother in the OVAs. Despite her youthful looks, Tennyo is 80 years old, and like her grandfather Katsuhito (Yosho), she often uses an older appearance when among others. Because of her similarity to Kiyone Masaki, Tennyo would often swap places with her and take care of Tenchi when he was a baby. She left right after Tenchi's mother had died, only to reappear when it came time to introduce Noike.
Once she had arrived back on Earth, her father Nobuyuki Masaki was supposed to pretend that Tennyo was Kiyone. However, when he overacted his role, Tennyo was forced to knock him out. Tennyo explained that since she is 80 years old, it would have caused an uproar if she had stayed with Tenchi, since some of her old classmates were still around. Katsuhito later explained to Tenchi that it is because that the Masaki family are forbidden to reveal their true identity to the people of the Earth, since Earth's civilization is still in the development stage, which is the main reason why Tennyo had to leave before.
After that, Tennyo left to go on one final trip together with her old classmates in Hawaii, with her grandmother Airi Masaki and came back just before her father Nobuyuki was to be married to Rea Masaki and then she attended the wedding.
Judging from information from Kajishima-sensei's doujins, Tennyo works at the Galaxy Police or for Airi. She also designed the armaments on the original Kamidake (Seina Yamada's ship)