He cannot even give himself a reason to rise from the ground until Fenris says "Get up."
He finds his feet then and follows when Fenris says to follow him. He thinks that before he was a hand puppet, manipulated from inside, and now he is a marionette. It's easier this way anyway, to put his marionette strings in someone else's hands and let them dance him along, rather than find the will to move himself. He's used to it (and empty now), and if Fenris uses him, perhaps it will expiate some of what he wrought with Vengeance.
He will let Fenris hold his strings, because Fenris will not let him misuse the Maker’s gifts again.The surface tension breaks and the first real emotion he has felt since waking explodes in his chest. It is caustic and (make it stop!) furious and his steps falter and stop while he sways on his feet with the force of rage and pain and betrayal on the behalf of all mages that boils away some of his heavy layers of calm.
He is keening without hearing it, he is not seeing the city street or Fenris turning with concern writ large on his face, he is not thinking of who or what he might attract with his escalating, grief-stricken, rage-stricken cry. Where he had been nothing moments before, now he is only a red beam lancing into the sky ready to-
Fenris slaps him. It isn’t hard or meant to harm, but the jolt startles him, and his wail is cut off by his indrawn breath.
“You will not do this,” Fenris snarls in the moment of Anders’ sudden silence. His eyes do not actually change color, but his heavy frown seems to shadow them, turning them from the green of new growth to a dark, secret green of damp moss in hidden places. He latches on to Anders’ upper arm and shakes him. “Do you understand?”
The keening is gone and the rage is receding, if not the pain. Its departure leaves room for another emotion on the lifeless shores of Anders’ dark lake. It struggles to the surface, half-drowned but there - gratitude.
Fenris shakes him again. “You will walk with me to my home in silence. Do you understand?”
This time Anders nods, and that seems to satisfy Fenris. “Good.”
They travel the rest of the way in the silence Fenris demanded, and his grip on Anders’ arm is a lifeline while the rage slips back under the lifeless waters and the simple sense of gratitude struggles not to sink back along with it.
Once inside Fenris’ mansion, he is released, and Fenris stalks away up the stairs. He can stay in the foyer with its corpses and mushrooms, but Fenris turns halfway up the stairs and scowls to see that Anders is still (haunting) standing in the entry room.
“Don’t just stand there,” he says impatiently. “Come upstairs.”