Hatchling

Before God left, He gave instructions for a new method of creating angels: one that allows an angel to take a consenting adult human as their child. By feeding them grace over the course of an unspecified amount of years, the human's - now known as a nestling's - soul will change enough to be able to produce a modified form of grace, thereby keeping angels from dying out. After the end of the apocalypse and with Sam having returned to Stanford, Dean is at a loss. When Castiel offers to take Dean as his nestling, Dean has no idea how far Castiel plans to take this - or how much he'll end up needing and enjoying it.