Originally Posted by
Fate/Zero Mats, Sola's entry
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.