Fate Testarossa is a former antagonist in Magical Girl Lyrical Nanoha. She was a mage who resided in the Garden of Time along with her familiar Arf, a dog person, and her "mother" Precia Testarossa. A girl, who took her work very seriously, was told by her mother to go get the Jewel Seeds. Fate herself did not know the reason for this task; instead, she tried to get the Jewel Seeds so that the memories that she had could be relived. She was a rival of Nanoha Takamachi, who later took an interest in trying to reform her.
When Fate collects about four Jewel Seeds, Precia berates her and severely whips her in episode seven. Fate could hardly move, although she went on for her mother's wishes. Arf eventually calls Precia out on her treatment of Fate and was thrown out, only to be found by one of Nanoha's friends.
While having one last battle with Nanoha over the Jewel Seeds, she loses, and Precia steals the Jewel Seeds. She then gets herself involved with the Time-Space Administration Bureau, where it was unfortunately revealed that all those memories that Fate had didn't belong to her, and that she was copied from Precia's real daughter Alicia. And, she also learned that Precia always despised her.
She then faints from this revelation. Even after this, she tries to help her mother and promised to protect her. However, the deranged woman chooses to stay with Alicia's body, and she falls into a dimensional void.
After this, she stays aboard the Asura, and she also brings her cell into her room. She stays in touch with Nanoha with video letters as well. It is also hinted that Lindy Harlaam planned on adopting her. And she starts to train with Chrono and reaches the AAA-rank. She later returns in A's, in which she becomes a temporary mage, and helps Nanoha fight Vita.