Morality Chain: The Morality Chain is a character who is the reason another character is Good. Stereotypically a female love interest, a mother, a daughter, or a little sister; as long as this person is alive, her target of affection will at the very least be a Noble Demon. If a Morality Chain were to fall, commit betrayal, or get seriously hurt or die, there is nothing to prevent a Face–Heel Turn happening so fast and so hard that the unchained character is gladly chopping his former teammates into pieces before you can say “Neutral Evil”. This is more than the Roaring Rampage of Revenge; everyone has to suffer.
Cain and Abel: Sometimes Sibling Rivalry can get a little… intense. Maybe one who Missed the Call gets overly jealous that the other has become The Chosen One, maybe grand powers or knighthood run in the family and one just happens to have been tempted to The Dark Side, maybe one of them betrayed their master or father and the other has to stop him, or maybe it’s just Because Destiny Says So, dammit. Whatever the case may be, now one’s the hero and one’s the villain, and they must do battle. Commence the angst.