Haiiro no Onmyouji

Sabatora, a boy whose parents were killed by "kuragari," works as an onmyouji for the Public Security Bureau to get revenge. His only friend is Kyue, a kuragari who been with Sabatora since he was a small child, and Sabatora sees it as a kind and gentle soul who is like family. One day, however, Kyue is attacked by Seto, a colleague from the Public Security Bureau who hates kuragari. Caught in a tough spot, Sabatora and Kyue undergo an unexpected transformation.

(Source: Natalie, translated)