When you were young, you went to school with Dean and Sam Winchester. The two brothers and yourself made a promise that you'd find each other when you were older. Now is time you do just that. You run into the things they've hunted for years. This fan fiction is an insert so by all means, have fun!
You are an immortal being, not limited to a species because even the Archangels have no idea what you are. Your only friend is Castiel, when he has time to visit. Even though you are over 6 million years old, you have very little control over your powers, so you stay inside to protect the humans from you. Then Castiel...
The reader is in a relationship with Dean Winchester, but one night something happens with Sam to change that. She doesn't want to hurt Dean, but doesn't know what to do. But then, the choice is taken out of her hands.