Fate Testarossa is the love interest of Nanoha Takamachi in the anime series Magical Girl Lyrical Nanoha. She first encounters Nanoha during the Jewel Seed Incident, when the two clash over the Lost Logia that Fate is attempting to collect for her abusive mother Presea. Defeated by Nanoha and abandoned by her mother, Fate eventually finds her new purpose in the service of theTime-Space Administrative Bureau, working together with them and with Nanoha to resolve the Book of Darkness Incident half a year later. Over the next ten years, Fate becomes one of the top Executive Officers of the Bureau, tasked with apprehending the interdimensional criminal Dr. Jail Scaglietti and later on, with investigating the activities of the Hückebein family.
As a child, Fate is always protected by her wolf-woman familiar named Alph. After Presea's presumed death, Fate is adopted by Lindy Harlaown, changing her name to "Fate T. Harlaown", and, in turn, adopts two children of her own, Caro Ru Lushe and Erio Mondial. After the JS Incident, she also becomes Vivio Takamachi's godmother.