Villianess Grandpa

He is an immortal that is bound to one area.
She is a princess driven from her home.

He tells her, "There are only five rules you need to follow."
1: Kill without hesitation.
2: Never listen to the enemy, kill before they attack.
3: If you see the protagonist, kill on sight.
4: My word is the law.
5: Look at rules 1-4.