Angelcest

Castiel and Anna in 4.16. 'On the Head of a Pin'

Angelcest is the commonly used term for Fanfiction focussing on pairings involving angels in a sexual relationship.

The term can be used for both slash and het pairings.

Angelcest is not always considered as incest by the fandom, since they are possessing vessels and them being brothers and sisters can be interpreted differently from the terms used for humans.

Angelcest often involves a metaphysical level of sexuality in fanfictions, that involves the connnection or sharing of grace.

Common angelcest pairings are e.g. Anna/Castiel or Castiel/Gabriel.