Trinity

When you turn 21, you get a guardian. 99% of the time, it's an angel, of course. However, for those with a high risk of being attacked, there's a chance you could get something else... a demon guardian. Your father is the head of a well-connected Mafia group, and today, your 21st birthday, he's giving it to you. Today you also get your guardian, and what do you know, it's a demon.