Demon On Your Shoulder

Every person had a daemon, an animal-shaped manifestation of their own soul, and bore a picture of their soulmate's daemon on their body. Everyone, aside from Jace. Because Valentine split his soul, giving him two daemons – and took the one on his soulmate's marks. So even when he meets them and recognizes them by their daemons, they don't recognize him. Magnus/Alec/Jace slash