Sousei no Onmyouji - Chapter 21

So If I understand right, Seimei is like the first Exorcist or at least some extremly powerful being and the little girl is being possesed by the mother of that spirit. This infers that Seimei is Rokuro’s guardian spirit but since he can be possesed that means they have a sort of symbiotic relation…. Or what would be even crazier would be that Rokuro is the reincarnation of Seimei