Sayo

A girl living in Yuba's village with her parents and her older brother Shin, when she was still a child her parents would die after an epidemic and She and Shin would become orphans and would be raised with a little of help of all of their neighbours, due to them being born with capacity of using spirit arts the same as Ruri they would begin to learn them together with her from Yuba that would treat her almost as siblings and that way she would become Ruri's childhood friend.

(Source: Seirei Gensouki Wiki)