The summary is as follows:
When a human child is born, their soul is shattered into bright gleaming pieces that scatter to the winds.
In this story, the moment a human being is born, their soul has special pieces that break off and attach themselves to another person’s soul. That means that those two individuals have some kind of connection. Whether as family member, as a friend, or something more, they’re linked together with a special bond, as if their hearts tie themselves together.
And then there’s the soul mate piece.
It’s a soul piece that’s usually larger than most. As a huge chunk of a person’s soul, it’s also the most important. It’s described this way:
The true meaning of a soul mate is simply the one person without whom a human doesn’t truly feel complete. It’s not a given that every human will even discover their soul mate piece.
Castiel is an angel. And, unlike humans, angels were not created to have soul pieces.
Until one day, the day Dean Winchester is born, Castiel is bludgeoned in the chest by a soul piece.
But not just another soul piece. It’s a soul mate piece.
To be perfectly honest with you, I was going to ignore this story at first. But when I started to read it, I was completely hooked by the writing and characterization and the plot. It’s just so believable and perfect. So much so that it’s amazing to me this isn’t canon.