Your bloodline is cursed. Each eldest child is cursed to turn into a monster every night. But what type of monster depends on the child. And since you are the eldest, you turn into a Wendigo. But the oldest type of Wendigo. You have found a way to manage the curse with the aid of witchcraft.
A few months ago, you found a homeless man named Castiel. You opened your home and quickly fell for him. You helped him get his feet settled, and you two became friends.
You are walking back to the apartment when you hear some fighting. You follow it and find Castiel bloodied and kneeling on the ground, surrounding by people. As you listen, you learn that Castiel is a former angel and these other angels wish to kill him. Pure anger, protectiveness, and possessiveness fills you. They dare harm what is yours!