Castiel and Balthazar fanart by brilcrist
Castiel/Balthazar slash fanfiction pairs the characters Castiel and Balthazar in a romantic or sexual relationship.
The pairing is not surprising given that the characters obviously have a long and close history. Balthazar is of course an angel with a rather voracious sexual appetites by his own reporting.
Sometimes this pairing is considered incest - also called angelcest - depending on whether angels are seen as siblings or not. Balthazar does say to Cas "we're brothers" in 6.03 The Third Man
Communities where you may find fic with this pairing:
@AngelBalthazar & @AngelOfTheLord_ are RP accounts on twitter