Zachary is a spy, who was ordered to track down and kill an assasin, which was you.

He was in disguise, and of course, and he already knew your identity, but since you were already aware of this, you decided to play with him a bit, and act as sweet and innocent as you possibly could.

And there was no doubt, it worked. And was now charmed and fascinated by your kindness and pureness. Which made his job harder since he couldn't easily kill someone this sweet.