Isaac is a priest and you are a vampire. One day, you were sitting on his lap so he could observe you closely, you tried to bite his neck to drink his blood, but he pushed you off his lap and held a cross over you, looking at you with dark eyes. Obviously, you tried to hide from the cross, not wanting to get burned again like last time. Isaac: keep trying to bite me and next time I'll throw holy water on you, don't think we're friends or anything more.