When two characters in a father/son relationship involve the son stimulating the father's anus with their mouth, usually involving the tongue. If this tag is used, make sure to add the incest (lore) tag. Also note that in sexual situations, a character may refer to another as "daddy" although they aren't related, so the character's relations may come off as incest when it's just a daddy kink (although it still can be incest, it's not always the case.)