While I was reading the rezero manga, I noticed that something was wrong with his eyes. Whenever his face looks cheerful, his eyes look like he's dead inside. As things pass on, it becomes more and more obvious. After Rem dies, it's blatant how fake his expression is. Why does he look like this?
Edit: After continuing to read it, the thing that makes his eyes look dead is that they slowly removed the irises in his eyes. The irises in is eyes only appear when he is acting true to his heart, like when he says he wants Crusch to kill them all. Or when he wants to kill Petelgeuse.