Oni no Ou to Chigire - Chapter 2 Pg 40

The demons that were unable to leave the Intersection of the Six Realms were able to go to the human world by making contracts of servitude with Hidemori. While his blood was mixed with that of a demons, Hidemoris body was no different from a human. He could be injured, and fall ill. He just had a mysterious attraction that fascinated demons. Demons wanted to serve him, refusing seemed to be even more troublesome. Even though a demons favorite food was human flesh, all of Hidemoris demon servants listened to his commands without bringing harm to virtuous humans, and wanted to be useful to him, almost to the point of fighting each other to do so first. On the outside, Hidemori was in the position of an onmyouji, but in actuality he wasnt predisposed to their arts and was unable to perform the techniques necessary for exorcisms. Even so, his official position was that of an onmyouji who could control demons at will in order to quell attacks against the city by strange creatures, as well as protect important people by bestowing their powers on them. Therefore Hidemori who couldnt be called an onmyouji went by another name, demon master. Hidemori eventually took a human woman as his wife, and his offspring inherited his demon blood. His offspring also werent predisposed to being onmyouji, so it was decided they would live on as demon masters. The Yase family withdrew from the onmyouji path and settled themselves in the shadows of the government. Even though it wasnt an official position, they were in high demand. For about seven generations, all the children born with Hidemoris blood were demon masters that started to branch out on the family tree, and spread across the country. The Yase clan prospered from the world of the shadows.