Morality Chain/Playing With

Basic Trope: Character is only reason that another character remains good.
 * Straight: Angelica keeps her older brother Damon's nastier side from surfacing.
 * Exaggerated: Damon teeters on the edge of Complete Monster, and the only thing keeping him from gleefully skipping across the Moral Event Horizon is Angelica.
 * Justified: Angelica and Damon have Twin Telepathy and Angelica is an empath. She routinely sends Damon positive emotions to keep him in check.
 * Damon had a very traumatic upbringing, and as a result hates everyone and everything except for Angelica.
 * Inverted: Kid with the Leash or Corrupt the Cutie
 * Alternatively, when Damon dies, Angelica begins to turn evil because she starts going insane.
 * Subverted: When Angelica is killed, Damon becomes even more devoted to fighting for good in her memory.
 * Double Subverted: Well, that's what it seems like at first, but he actually becomes brutal and obsessed with vengeance.
 * Parodied: Damon is a psychotic, Spikes of Villainy-wearing Sociopathic Hero who turns completely harmless when Angelica is around, and Angelica refuses to believe he's anything else.
 * Deconstructed: Because she has to keep Damon in line all the time, Angelica can't live out her own life and is just as chained to his side as he is bound by her existence. Mutual resentment gradually weakens the bonds between them until something finally gives way.
 * Reconstructed: Eventually, Angelica rubs off on Damon; he starts to become a genuinely good person even when she's not around, so eventually, he doesn't even need a morality chain to be a good person.
 * Zig Zagged: Anegelica's presence prevents Damon from committing evil deeds half the time; it has no effect on him at other times.
 * Averted: Angelica's presence has no particular positive effect on Damon's behavior.
 * Enforced: The director says he can't see why Damon is on the good guys' side when he's much meaner than any of them, so the writers add Angelica to give him a reason to stay.
 * Lampshaded: "Now that the meddling fool is out of the way, I'm going to kill you!" "Damon, what are you doing?" "Crap, Angelica is back! For some reason this ruins everything!"
 * Invoked: Angelica was deliberately raised to be her brother's keeper and balance out his bad side.
 * Defied: "What, you thought I'd spare you because my little sister was around?"
 * Discussed: "I always feel like Damon would kill us the moment our backs were turned if Angelica wasn't around."
 * Conversed: "He's one of those characters that only stays good because his sister is watching. I bet they'll kill her off or something eventually so we can see him really snap."
 * Played For Laughs: Angelica keeps Damon in line by terrifying him, despite being The Cutie in all other respects.
 * Played For Drama: Angelica is targeted by people aware of how important she is to Damon in order to get Revenge by Proxy.

The only reason I'm letting you live long enough to go back to Morality Chain is my sis, got it? Anything happens to her, I'll kill you, grind you into hamburger, and feed you to your mother, and if you're lucky, it will be in that order.