After a long and desperate struggle, our hero stands triumphant. The evil tyrant has been cast down from his throne and our hero’s swordpoint is at his throat. As our hero gets ready to make that fateful swing, the villain tells him, "No, you can’t do this. You need me!"
The nature of this plea can vary greatly. It may just refer to the hero(es) personally (such as villain being the only thing keeping their lair intact), or it may involve the world as a whole (when removing the villain will result in an Evil Power Vacuum, for example). The reality of the claim varies as well; it may just be a villainous ploy to throw the hero off his game. In any case, these pleas are rarely successful.
If the villain really is directly responsible in some sense for the well-being of the world, he is a Load-Bearing Boss. If, after he is cast down, worse forces arise, it may be a case of Better the Devil You Know, or the chaos of an Evil Power Vacuum. Whatever the reason, if he's telling the truth, killing him would be a clear case of Nice Job Breaking It, Hero.
Compare Can't Kill You, Still Need You, a role reversal where a villainous character realizes that they actually do require the continued existence of their victim (for whatever reason), and refrains from killing them as a result.
- Dragon Ball Z: Babidi tries this line when Piccolo attacks him, saying that he's the only person alive with any kind of control over Majin Buu, and if he's not around then Buu will run wild and destroy everything he sees. Piccolo points out that Babidi was planning on using Buu to destroy everything on the planet anyway, so he doesn't see how that's an improvement.
- Yu-Gi-Oh!: In the English dub of the Battle City Tournament finale, Yami Marik tries this to convince his saner self not to forfeit the duel (and by extension erase him from existence). What little reason he gives besides the obvious is that Marik needs his ruthlessness. Given that he's a. an Ax-Crazy Stupid Evil Omnicidal Maniac, b. the embodiment of Marik's trauma and villany, c. the true identity of Marik's father's murderer (whom Marik had previously believed to be the Pharaoh), and that d. he'd been using Sympathetic Magic to make Marik himself into a Human Shield only seconds prior, Marik doesn't buy it.
- In the second Superman versus Spider-Man crossover, Doctor Doom discovers that the reactor he invented as part of his master plan is about to explode, and tries to flee, only to be caught by Superman. He then shouts "Let me go! My genius must be preserved!!" (Superman didn't know about the incoming explosion at the time.)
- Captain America: The Winter Soldier ends with an unusual heroic example, that also incidentally demonstrates why it's normally a villain trope - because when a hero can admit to having been disastrously wrong and care more about not being punished than trying to prevent the same situation from happening again, it looks like Protagonist-Centered Morality.
Natasha Romanoff: You're not going to put me in a prison. You're not going to put any of us in a prison. You know why? Because you need us. Yes, the world is a vulnerable place and yes, we helped make it that way. But we're also the ones best qualified to defend it.
- Downfall: Henrich Himmler, realizing that the war is lost, leaves Berlin to negotiate peace with the Allies. His Number Two, Hermann Fegelein, questions Himmler's intent but Himmler insists that the Allies need order in Germany and that his SS will be able to provide such order (with him naturally in charge of course). What he fails to realize is that the Allies would not agree to any peace treaty that pardons the SS for their crimes against humanity.
- In Revenge of the Sith, this is the climax of Darth Sidious' quest to corrupt Anakin Skywalker into his apprentice. Mace Windu has him at lightsaberpoint and is about to execute him, so Palpatine plays to his desperate desire to save his wife from death at any cost. Needless to say, it works.
- A more personal variant occurs in Transformers: Dark of the Moon. As Optimus Prime and Megatron face off once again and with Megatron on the ropes, the Decepticon asks for a truce to lead his remaining forces in peace, asking Optimus what he would be without a villain to fight.
Megatron: Who would you be without me, Prime?
Optimus: Time to find out.
(Optimus promptly decapitates Megatron.)
- The Elric Saga: Darnizhaan tells Elric and Dyvim Slorm that killing him will begin the death of the world they know. They decide to do so anyway.
"Fools! In destroying me, you destroy yourselves!"
- Mistborn: The Lord Ruler. "You don’t know what I do for mankind." Surprisingly, he was largely telling the truth. On the other hand, he may not have been sane enough to keep doing what needed to be done.
- The Manual of Detection: Shortly before he’s shot, Arthur, the Overseer says "You know what that madman's doing to my city. To our city. You need me."
- In The Great Ace Attorney, Lord Chief Justice Stronghart ends up resorting to this when exposed as the one behind the Professor and the Reaper conspiracy, arguing that the knowledge of someone of his rank being involved would shatter faith in the British legal system. Queen Victoria, however, decides that making sure he pays for his crimes is worth it.
- Half-Life 2: Dr. Breen tries to convince Gordon that he, as humanity's go-between for the Combine, is the only hope for the survival of the species. No one else really seems to buy it, though.
- In Portal, GLaDOS tries this. Being GLaDOS, she's not very good at it.
"Who’s going to make the cake when I’m gone? You!?"
- In Resident Evil 6 , Derek Simmons, the head of the Family tries this during his boss battle... fruitlessly.
Simmons: You... have no idea... what would happen if I DIE!!!
Leon: The world would be a better place!
- Justice League: In an alternative universe, President Luthor taunts Superman that he loves being a superhero and thus he needs a supervillain to fight against, which is why Supes wouldn't kill him despite nearly causing a nuclear war. His argument proves to be too persuasive, as this Superman decides to forsake his love of being a hero and instead establish an authoritarian regime upon Earth, starting with Luthor's execution.
- In The Simpsons, after Bart and Lisa proved Sideshow Bob rigged the election to win his Engineered Public Rant ends with one of these. Essentially making this statement the source of his downfall.
Sideshow Bob: Because you need me, Springfield. Your guilty conscience may force you to vote Democratic, but deep down inside you secretly long for a cold-hearted Republican to lower taxes, brutalize criminals, and rule you like a king. That's why I did this, to protect you from yourselves. Now, if you don't mind, I have a city to run.
Judge: Bailiffs, place the mayor under arrest.
Bob: *is handcuffed* What!? ...oh yes, all that stuff I did.