Haiiro no Onmyouji

Seiko is an exorcist working for the Public Safety diviners' office in a world under attack by man-eating beasts/spirits(??) known as "Twilight." Every night at the third hour of the ox(?), his work of hunting and banishing the creatures begins. But Seiko has one dark secret: His only remaining family is a Twilight named Kyue, whom he's harboring in his own home! When the truth comes out to Seiko's superior officer, however, Seiko's life turns upside down—because anyone supporting the Twilight becomes branded as a traitor, and the wanted posters of him are just the beginning...

(Source: Yen Press)