Back to the Beginning (слэш)

The Darkness is taking over. God is dead, Amara is winning, and there's nothing left that anyone can do. Sam's watched his friends and family slowly fall to the dark that's sweeping over the planet. Soon, there'll be nothing left. No world left to save. There's no hope left for them. All Sam can do is cling to the one being he loves more than anything else and wait for the end to come.
That is, until Gabriel pulls out a random Hail Mary and comes up with their only chance to make things right. With every last bit of his power, he throws Sam back into the past in the hopes that maybe he'll be able to fix the future.