Reki
About
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)