He still remembers the first time he saw her.
It's unusual for him, as he usually tries not to think about his contracts after they're finished. It's not a matter of shame or guilt for what he has done, just a simple matter of 'I don't really give a shit' and as long as he got away clean and the money is sitting in his account, whatever fallout isn't his problem. Killing is a job, it's what he was created to do, what he'd been trained all his life to do. He doesn't get paid to have emotions. In fact, usually he operates as though he doesn't have them at all. And why not? He's been suppressing them for so long sometimes even he believes that he doesn't have them.
And then she came along.
Now as he sits on the edge of the bed, clad only in his underwear and staring out the window at the brick wall of the next building over, he can hear her breathing. Soft, whispering breaths that can barely be heard over the sounds of the city outside. But he can hear them - he listens for them, almost as if he's afraid that one day they'll stop.
Finally he turns, hitching one knee up onto the bed and looking over his shoulder. He watches her sleeping form, the soft rise and fall of her shoulders as she breathes. The way her hair curves along her back and disappears under the lone sheet that is covering her. The outline of her legs, bent at the knees and curled up against her chest; the angular space where the sheet descends back to the mattress with nothing else to hold it up.
She is his reason.