Shadows of the Lost | Martineau, Maxym M.

'As a member of the Charmers Council, Gaige is able to form lasting bonds with the magical beasts of his world. At least, he used to be a Charmer...until he died and was brought back as one of the immortal assassins of Cruor. Now he's far more dangerous. ...and something beyond the shadows lies in wait, hungry to claim him for its own. As leader of the assassins, all Kost can do is watch as Gaige struggles with his new life day by day. He wants nothing more than to ease Gaige's suffering-yet how can he when they both know he's the one responsible? There is nothing left but bitter memories and hopeless longing between them. Yet when Gaige is lost to the shadow realm, Kost is the only one with any chance of bringing him back: if they can learn to trust (and perhaps love) each other again'--