From my understanding of what transpired was; The invincible sun witch was leading them to glory in wars. This witch then suddenly went missing which costed them huge loss (including the niece and nephew of this commander). Kaya losing her ability to regenerate after being struck by the moonsword thingy, was being treated by Elkin. After her power came back to her, she just straight up get back into the war and ended the whole things with the Northerners. It should go like this from what I can remember since Kaya only ever get hurt once during the war, and the one responsible for it was this dumbo delusional commander