Hope
At first Hades thinks it a fool's errand, if not worse. Even if Persephone had been moved by the boy's song, he's lived through too many betrayals, too much time away from her, to be moved by a song of love, of all things.
He's half-tempted to execute Orpheus now and get it over with, but his wife's hand on his shoulder stills him. Even with their marriage in this sorry state, Persephone thinks there's something worth saving, and he can only hope she's right.
And as the boy plays on, memories stir in Hades' chest. He remembers meeting her, smiling at her, begging her to come home with him, dancing like nothing else in the world mattered.
And as he turns to look at her, tears trickling down their faces, Hades feels hope flutter in his chest that maybe not all is lost.