Reki

Reki was born in a district outside of the Slayer organization's influence. She lived her early childhood in the northwestern Aizu. When the demons destroyed her home ten years before the main story, Reki was saved by Rinne. Reki was raised within Shiranui Village and trained by her chief to defend herself.

In spite of the Shiranui chief's denunciations, Reki admired the heroism associated with the Slayers. Reki felt it was counterproductive to humanity's future when Rinne declared independence from them and left her foster home to join their cause. Soon after she left, she approached Souma's Hundred Demon Corps unit. Reki scatters Kuyou and Souma's skepticism of her loyalties by helping them defeat a Kazenui. Convinced of her usefulness, she is granted official membership and accompanies them to Utakata Village.

(Source: Wikipedia)