Sola-Ui Nuada-Re Sophia-Ri

Daughter of the noble Nuada-Re bloodline, which boasts considerable behind-the-scenes influence within the Association, and Kayneth El-Melloi Archibald's fiancé.
Generally, families of magi make it a rule to only pass down their secrets to a single successor, while keeping any other children they may have ignorant of even the existence of sorcery itself. However, at the time Sola-Ui was born, the Nuada-Re family was embroiled in a tumultuous power struggle, and there was a very real fear that their legitimate heir could be assassinated. As a result, they enacted a plan to train both the older brother and the younger sister in the rudiments of sorcery, so that either one could inherit the family crest.
In the end, though, the conflict died out before anything happened to either child, and Sola-Ui's older brother was given the crest and the title of successor. Sola-Ui, on the other hand, was no longer of any use to her family, and her very existence was disavowed. She became a mere tool to be given away in a political marriage, where her excellent physical capacity for sorcery and childhood training would allow her to serve as an assistant for some first-rate magus.
However, Sola-Ui did not harbor any resentment toward this treatment. To be perfectly frank, she didn't even understand what “likes” and “dislikes” were in the first place. While it's certainly true that she always
selfishly toyed with those around her, that was simply because it was ingrained in her from a very young age that acting in a way that would preserve her value as a noble was the secret to success in life. Sola-Ui herself had never truly wanted or hoped for something even once since being born.
Consequently, she didn't care one bit whether the attraction caused by Diarmuid's mystic face was real love or not. For her, the simple sensation of passion boiling up from the depths of her heart was her greatest treasure, and she had she had no intention of giving it up after she had finally obtained it. Because, passion is the very thing that gives life value.
…When Nasu Kinoko heard all of that, he started writhing around muttering something that sounded a lot like “It's a perfect moe bull's-eye…!”

Fate/Zero material: Fate/Zero Encylopedia