American Girl and Seta's Adoptive Daughter.
Sarah once resided in California in the United States before her biological mother, Julia, died while in college during archaeological expeditions with Seta Noriyasu and Haruka Urashima. She would wind up being adopted by Seta and travel with him on all his expeditions. The anime adaptation of Love Hina would imply that Sarah got adopted by Seta due to abuse she suffered from relatives.
Sarah was a character created for Ken Akamatsu's Love Hina manga series. She was originally going to be made into Haruka's biological daughter for the series, but the idea was scrapped. Sarah appears in all anime adaptations of Love Hina that include the TV anime, Christmas special, Spring special and Love Hina Again OVA series. She is voiced by Yumiko Kobayashi in Japanese and Julie Maddalena in English.
Sarah is nine years old during her first appearance in the series, having long blond hair and blue eyes. Being a tomboy, Sarah normally dresses in masculine clothes with a preference for wearing pants with overalls.
Sarah has a bit of a mischievous personality as she often likes to cause trouble and pull pranks on others. Because of her attachment to her "papa" Seta, Sarah will often try to drive away anyone whom she perceives as trying to take attention away from her adoptive father. She will usually pull a two-faced act to seem like an innocent girl in front of others to drive attention away from the trouble she causes for whomever she torments. Sarah was trained in martial arts by Seta and will usually use such attacks and any artifacts she can find on anyone who annoys her.
Sarah first appears to make Keitaro's life miserable by throwing random artifacts at him or beating him up with the martial arts moves that she learned from Seta. She takes up temporary residence at the Hinata-sou when Seta goes on another expedition as he feels Sarah should live a regular childhood. While at the inn, Sarah becomes fast friends with Kaolla Su, becoming "partners in crime" as both are foreigners, like changing their hairstyles to resemble the other and cause mischief for the other inn residents.
While bathing with the other girls, Sarah normally wears a bathing suit as she tries to avoid exposing a panda-shaped birthmark on her butt, which greatly embarrasses the girl as such where she had never even told Seta about it. Keitaro discovers this secret and uses it as blackmail to keep Sarah from causing any further problems for him in the manga.
When Haruka and Seta get married in Molmol later in the series, Sarah would return to traveling with them on their worldly expeditions.