The wings that you have is the opposite color of your soulmates wings. For example; Black and white go together. When you meet your soulmate you just know it and it's the best feeling in the world. John felt that way with Mary. They both died unfortunately and they were buried. So, Dean and Sam are on there own. When you turn 16 you first get your wings. Dean is turning 16 and so is Castiel. Dean doesn't know Castiel exists and Castiel doesn't know Dean exists. That is until Castiel gets transferred to Dean's school.

The angels have fallen. Castiel lost his grace, and is now a human. He experiences hunger, cold, need, but still pondered at the thought of love. Dean takes him under his wing and helps him understand his new way of life; every aspect. Even though his grace is lost, the affair between a man and an angel is forbidden. Not to mention, an angel and a Winchester. In addition to the internal conflicts between the two, they also have to worry about the bounty put on Castiel's head by the other fallen angels.