Can't Kill You - Still Need You

When one person spares the other's life (despite really wishing to kill him on the spot) because he intends to use him later.

One response to Get It Over With. If a lesser villain is Genre Savvy, he may make sure his boss always needs him, lest he outlive his usefulness. Can also prompt Stop or I Shoot Myself to put the boss at a disadvantage.

Can apply to both good and bad guys. Compare to Enemy Mine. Contrast You Have Outlived Your Usefulness. Compare/contrast Sympathy for the Devil.

Anime and Manga

 * The villains in both incarnations of Fullmetal Alchemist need the Elric brothers alive to fulfill their respective master plans.
 * Likewise, the Elrics end up needing  in the manga for his literacy skills in order to decode  's counterplan to the villain's master plan.

Film
"Jack Sparrow: "And me, for example, I can let you drown, but I can't bring this ship into Tortuga all by me onesies, savvy? So, can you sail under the command of a pirate, or can you not?""
 * The first Pirates of the Caribbean movie has Jack and Will steal a ship, then fight when Jack tells Will his father was a pirate. Jack gets Will down with a sword to his neck, then reverses the sword, admitting he needs Will to sail the ship.


 * Later in the film, Elizabeth burns all the food, the shade, and the rum to signal a passing Royal Navy ship. Jack pulls out his pistol in a rage to shoot her, but stops himself. In order to reclaim the Black Pearl and rescue Will, he will have to smooth-talk his way onto another ship. Which, thanks to Elizabeth, will be a Royal Navy ship. Shooting Elizabeth would remove the only thing keeping them (or Will) from executing him on sight, as well as waste the one shot he's been saving for Barbossa.
 * It should be noted that it's an established part of Jack's character that he's reluctant to kill, which hampers his effectiveness as a pirate. He may stab people in sword fights or shoot the man who marooned him (who, it should be noted, was in combat with him at the time), but straight up executing Elizabeth isn't really in his nature. It was likely a sort of Black Comedy.
 * In At World's End, Jack tricks Beckett into thinking this by telling him he can convince the other pirates to meet Beckett's armada head on rather than holing up in Shipwreck Cove.
 * Sort-of used in Disney's The Hunchback of Notre Dame, though the main reason Frollo can't kill Quasimodo as a baby is that the Archdeacon caught him trying and guilt-tripped him out of it. He does, however, state that he's going to find a use for the "foul creature."
 * In Street Fighter, this is why M. Bison allows Dhalsim to live after Dhalsim makes the mistake of pressing Bison's Berserk Button by calling him psychotic.
 * In "Abandon Ship" there are too many survivors for the one lifeboat. Most of the people are left clinging to the outside of the boat but the captain allows one passenger to pull his huge dog in. The dog's owner is incredibly grateful but another survivor demands to know why the dog gets in while he doesn't. The captain's answer was "If we're not picked up immediately we could be out here for a long time. If that happens, we can't eat you." Cue the horrified look on the dog owner's face.

Literature

 * Happens more than once in Duumvirate. The biggest example is when William wants revenge on his creator for enslaving him to his own brother, but this trope kicks in instead.
 * The Lord of the Rings: The dynamic between Gollum, Sam, and to some extent, Frodo.
 * In Max Barry's Machine Man, the Corrupt Corporate Executive Cassandra Cautery has this in mind for . She plans to keep him alive so Better Future can calibrate its weaponized parts for Super Soldiers.
 * In the Warrior Cats series, the Big Bad, Tigerstar, decides to spare Featherpaw and Stormpaw because he thinks they may still be useful to him. (Presumably as hostages, since they're the children of his enemy's best friend.)
 * This is Mara Jade's opinion of Luke Skywalker in The Thrawn Trilogy. She wants revenge for the death of her old master, the Emperor, but always finds herself relying on him for survival or some other more immediate problem.
 * In the second book of the Chaos Walking trilogy, the protagonists finally have the Big Bad at their mercy. Then,  against all humans, and they realize that they need him to command his army in order to survive.

Live Action TV

 * The main plot of season 4 in Breaking Bad. can't kill Walt and Jesse because he has no one else to cook meth.
 * Fringe
 * Spike pulls one of these in one of the earlier Buffy the Vampire Slayer seasons, when he needs Angel to heal Drusilla.
 * In Supernatural's seventh season, does this to Crowley.

Video Games

 * Dragon Age: Origins: If you already know the final Reveal, this may become a motivation to spare the life of and instead recruit him to the Grey Wardens. Riordan tries to argue in favor of doing so without publicly stating why.
 * Starcraft II: It is revealed that.
 * This is the standard Paragon outcome to Zaeed's quest in Mass Effect 2. If you've already completed the final mission at this point, however, you can leave him to die instead.
 * Fable III: If you choose to spare Logan in the third game, the Hero Prince explains that "now is not the time for revenge.", politely asking for his brother's help. A kind way of putting it- you spare Logan because you need his built-up military to assist you.

Webcomics

 * Dominic Deegan includes a couple of these. Notably, Evil Necromancer older brother Jacob including 'don't kill Luna' as a major part of his demands when negotiating with the Shindula, simply because he expects to get some use out of her...for now.
 * Of course, he has his Heel Realization and saves her just 'cause at the end of the arc. "Don't say I never did anything for this family."

Western Animation

 * In the final episode of the first season of Young Justice, Vandal Savage notes this about, explaining that they are still needed for Phase Two of the plan,.
 * Evoked by current Big Bad Amon in The Legend of Korra, ridding the new Avatar of her ability to bend and killing her at this stage of the game would only create a martyr so he fully intends to face her last.