Why does Nora's darkness/corruption not affect Yato (or any other God that has named her, for that matter)?
As ton.yeung and I have stated in our comments, the Blight forms based on the guilt of the Shinki, therefore, if the shinki was committing sins under the notion that it was wrong, blight would occur, like in Yukine's case of destroying the school windows and stealing. But in Kugaha's case, he believed what he was doing to be for Bishamon's sake as shown in this scene.






Therefore, in Hiiro's case, she believes all the horrible things she did was for the sake of Yato and therefore was justice, so she was not blighted.