ルシカ

The being Sora repeatedly refers to as 'that shinigami', a creature so powerful and ancient that it cannot exist at the same reality as Sora and the others.  It is completely and utterly inhuman, devoid of mortal emotion.  It is one of the 'Originators' of the enja as a whole, along with the demonic blood.  Sora sees it as female, but even he admits that he isn't sure.  Specifically, she created the 'genryuu', and she decides whether they are obeying the contract she engraved in their bloodline.  If a genryuu loses her protection, they become as subject to corruption by their demonic blood as a normal enja if not moreso.  However, a genryuu who is obedient to their contract to destroy all demons they encounter will be blessed by her (her blessing also being as much of a curse as the powers of an enja).  She hints that she is also the originator of humanity, but Sora considers that to be an exaggeration.