The characters are in a situation that can only be resolved with a Heroic Sacrifice. So they send someone who can't die (or is already dead, either in the literal or virtual sense) to "sacrifice" themselves.
For example, Superman "sacrificing" himself by throwing himself over a grenade. Superman is, well, Superman. He is not affected by a mere grenade, it would need to be made of Kryptonite or magic to hurt him. Whether Superman knows it won't hurt him at the time is irrelevant to the trope, it only matters that it didn't affect him.
If the characters actually sacrifice themselves in a way that doesn't mitigate the sacrifice, that's not this trope.
- Since all Digimon in Digimon Adventure reincarnate eventually, given enough time, this applies to them. Specific examples include Angemon in the original, and Wormmon in its sequel, Digimon Adventure 02. Both sacrificed themselves for their Chosen Child partner and both were up and about in their baby forms within the next two episodes.
- In Yugioh 5 Ds Yusei's ace monster, Stardust Dragon, has this as its ability: it sacrifices itself to negate card destruction, but it will come back from the Graveyard during the End Phase to be used again at his leisure.
- In the first episode of Code Geass, C.C. takes a bullet for Lelouch. Since she has Complete Immortality, all it does is put her out of commission for a while.
- Happens in the The UK run of the Transformers. The "City of Fear" arc is in fact a self-contained Zombie Apocalypse setting, complete with a former Autobot Mad Scientist responsible for the zombie plague. The scientist, for the record, wants to build a giant engine on Cybertron and turn it into a spaceship. Let's just say that he's a bit nuts and his design isn't nearly as sound to the science as he thinks it is. When the engine threatens to explode and take the planet with it, the Transformers who survived the zombie attack have to send one of their own to die in the reactor to shut it down. The half-alive corpse of former Wreckers leader Impactor, who had previously menaced the Autobots as a mindless zombie at the scientist's command, overcomes his Ghost Amnesia and throws himself into the reactor, shutting it down in time to save Cybertron. Seeing as he was already undead at that point, he didn't want to live as a monstrosity and declared he was the natural choice to go into the reactor and stop it, at the cost of his unlife.
- In Frozen, Anna, dying from frozen heart curse, notices Hans about to kill Elsa, and throws herself between them, abandoning the chance of being saved by Kristoff's True Love's Kiss. She freezes solid moments later and Hans' sword freezes too and shatters upon striking her. However, Anna's Heroic Sacrifice turned to be the "act of true love" (in this case, sisterly love) that will break the curse, and seconds after she thaws from inside out. Therefore, Anna saved not only her sister, but also herself, and their kingdom, too, as she gave Elsa the clue how to fully control her ice powers through The Power of Love and reverse her accidental Endless Winter.
- At the end of Big Hero 6, Baymax uses his Rocket Fist to launch Hiro and Abigail through the portal, stranding him in the void. At least, not before hiding his data chip in his fist so that Hiro can rebuild him later on.
- The Cheshire Cat takes a beheading for the Mad Hatter in Tim Burton's Alice in Wonderland (2010). This trope applies because the Cheshire cat can detach his head from his body at any time.
- The Bowler throwing her ball (containing the spirit of Carmine the Bowler) into the Psychofrakulator in Mystery Men.
The Bowler: Now, the good news is you're not going to die, because you're already dead.
- An unintentional one (or two) in Constantine: when the titular hero is unable to stop the villain from starting the apocalypse, he slits his wrists, knowing that Satan will come personally to collect his soul. On Satan's arrival, time stops, letting John tell him what's going on. Satan barges in, curb-stomps the villain for usurping his job and offers John a favor, and the latter asks him to release one innocent soul from Hell. However, those two sacrifices redeem Constantine from his previous sins and he starts to ascend to Heaven. Enraged, Satan resurrects him and rips his lung cancer away, so he may have more time to sin again.
- X-Men: Days of Future Past: The X-men have survived repeated Sentinel army attacks by using Shadowcat's Mental Time Travel to avoid the encounters entirely. So long as she's kept alive long enough to affect the timeline, the (frequent) deaths of the others will be reversed.
- In Black Panther, T'Challa throws himself on a grenade to protect a room full of people. Not only does this not harm him, it charges up his energy-absorbing suit.
- There's a children's story about seven brothers who all look identical, but each has a different magical immunity (one is immune to fire, one cannot drown, one can't be cut, and so on). One of the brothers is unjustly sentenced to death, but when the method of execution is announced, the brother who is immune to that death secretly takes his place, and after a week of trying different methods of execution and getting nowhere the authorities give up and let him go.
A variation of this is found in the book The Five Chinese Brothers, where one of the brothers did cause the death, but only because he couldn't hold the sea in his mouth any longer (and tried to signal the boy that drowned). For the record their powers are Swallowing the Sea, very strong neck, very light, can stretch his legs, and can hold his breath for days.
- Harry Potter:
- During Dumbledore's duel with Voldemort, Fawkes the phoenix swallows a killing curse, causing him to burst into flames and die. Being a phoenix, of course, he immediately rises from his ashes as a chick.
- In the final book, Harry learns that he has to die, since he's a Soul Jar for Voldemort. Fortunately Voldemort's new body was made with Harry's blood, which anchors him to the living world. Harry didn't actually know this would happen and fully expected it to be a Heroic Sacrifice.
- In the second book, someone avoids death by the Basilisk, being only petrified, because instead of seeing the Basilisk's eyes directly, he saw them through Nearly-Headless Nick, a ghost. It's not clear whether Nick took the full blast of the Basilisk's power deliberately or just happened to be standing between the student and the basilisk.
- Played with in Charmed Life. Cat (who has nine lives) is going to be killed so that his evil sister can stay in her new alternate reality. He's pretty okay with it since it will mean that he won't have to deal with her any more and since he has lives to spare, unlike any other potential sacrifice. Of course, his sister shows up to tell the people about to kill him that they'll need to kill him a few times since he has several lives left. At this point, Cat realizes just how evil his sister is.
- In The Dresden Files book "Death Masks", when Harry is captured by fallen angels, Shiro, the oldest Knight of the Cross, takes his place to be tortured and later killed. At the end of the book, it is revealed Shiro was suffering from terminal cancer, and as such was doomed to die anyway.
- In C.S.Lewis's The Lion, the Witch, and the Wardrobe, Aslan the lion is sent to sacrifice himself to the White Witch in order to save Edmund, a prisoner of the White Witch whom he saved. The morning after the sacrifice, however, Lucy and Susan discover he comes back to life. He says then that while the magic law that required his execution was deep, there was a deeper magic still that resurrected him.
- The above C.S. Lewis example is, of course, inspired by The Bible, wherein Jesus Christ dies as part of a Xanatos Gambit by God to save the universe from the power of sin. Since Jesus is himself a part of God, he only stays dead for a couple of days and then comes back.
- In The Vampire Chronicles, Memnoch the Devil describes the Crucifixion as this. Against his urging, Jesus died knowing that he was God incarnate, rather than suspending his omniscience and experiencing the pain and fear of death as a human would. Memnoch argues that that negates the purpose, since God knows he's not actually losing anything.
- Doctor Who:
- In the episode "Utopia", a launch can't be completed unless someone goes into a deadly-radiation-filled room to flip some switches. They just so happen to have Captain Jack Harkness - a man with Resurrective Immortality - along, so he goes in to do it.
- All of the Doctor's sacrifices are technically negated as they just regenerate. On the other hand, it's always a very Painful Transformation, and they're never quite the same afterwards.
Tenth Doctor: Even if I change, it feels like dying. Everything I am dies. Some new man goes sauntering away...and I'm dead.
- Happened in Farscape. Aeryn, Crichton, D'Argo, Zhaan, and Stark are all captured while aliens tried to figure out who attacked one of their ships (they had all been aboard Talyn when he had opened fire, then escaped leaving them to get caught). Everyone tells a different story, so in the end the annoyed aliens declare they'll execute ALL of them by disintegration. Stark then 'admits' to the crime, whispering to the others that his powers gives him a reasonable chance to recover from disintegration; the only reason he hadn't volunteered from the start was that he didn't know what method of execution they'd use. Sure enough, he's disintegrated, the others go free, and some episodes later he reappears, having 'reintegrated' thanks to his powers.
- In this case, Stark really IS to blame. His realization that he is guilty, combined with his ability to survive dispersal, make him decide to sacrifice himself.
- Subverted by Nathan from Misfits.
Nathan: (RE: a virtual stranger who's just been killed in front of the group) Better him than me!Curtis: You can heal.Nathan: Better him than one of you!
- However, he does later volunteer himself (very reluctantly) to be temp-killed to save the others, although he doesn't actually have to go through with it.
- Also played straight the very first time he used his power: Nobody knew he would come back from killing himself to take out the Virtue Girl until he woke up in a coffin afterward.
- Inverted and played for laughs in the last episode of Series 2 (the Christmas ep). Despite constantly forgetting that he's immortal when faced with dangerous situations, for once, Nathan realizes that he has nothing to fear from an armed gunman and steps up as a human shield. As he starts taunting the guy, daring him to shoot, the others have to remind him that he had just given up his powers earlier that day. Oops...
- In Red Dwarf while temporarily transformed into Ace, Rimmer jumps onto an Emohawk that had turned into a grenade. Being a hard-light hologram, Rimmer is undamaged, though admits he didn't know that would happen.
- Zigzaged in BIONICLE. One of the Toa Inika has to volunteer for a sacrifice so they can claim the Mask of Life. Matoro volunteers. So he dies. Immediately after this, he is revived, because the mask was testing his willingness to sacrifice himself. However, actually using the mask kills you, and once again Matoro volunteers.
- The original ending of Fallout 3 has either the Lone Wanderer or Sarah Lyons receiving fatal radiation poisoning while activating the water purifier before it explodes. However, installing Broken Steel lets you instead send any of your three radiation-immune teammates (a Super Mutant, a ghoul, and a robot) to do the task unharmed, which they refuse to do in the base game for no reason at all. Although, even if you do still do it yourself, Broken Steel has you recover inexplicable (even though Lyons won't).
- At the end of the Fallout: New Vegas DLC Lonesome Road, you are faced with a Sadistic Choice between firing a barrage of nukes into the Mojave that will seriously cripple the factions vying for power there, or asking your robot buddy to stop the launch at the cost of destroying itself. The Tear Jerker aspect of the second choice is played up for all it's worth... except for the fact that the robot is basically a copy of another robot buddy, the original model remains completely intact, and the destroyed copy manages to broadcast its memories and upload them into the original before it is destroyed.
- Final Fantasy VII has Cait Sith volunteer to stay in the incredible shrinking temple, because he's only a stuffed toy and his controller is elsewhere. A few minutes after he does so, Cait Sith No.2 joins the party, who turns out to be indistinguishable from No.1. He's even got the same equipment No.1 had on him when he got crushed into a singularity.
- Naturally, Final Fantasy VII: The Sevening parodies this by having Cait Sith die constantly. As of the Wutai arc they're on Cait Sith #9.
- And that's not even too far from the canon truth, either - by Dirge of Cerberus they're on #4, and he dies after a Stealth-Based Mission too.
- In this case, Cait Sith's not-sacrifice was intended to make the player think Death Is Cheap, which made Aerith's permanent and unavoidable death all the more shocking at the time.
- At the end of Raidou Kuzunoha VS The Soulless Army Gouto-Douji (Who is cursed with Who Wants to Live Forever?) takes a ride on a missile to make sure it hits its intended target. He even notes his actions won't really kill him (hence why he is back in the sequel).
- Thane Krios from Mass Effect 2 has this as his reasoning to go on the Suicide Mission. He is an assassin suffering from a Convenient Terminal Illness, so he doesn't expects to live long. It can be a Subverted Trope too: If you know what you're doing during the Suicide Mission, it's possible to pull off the Everybody Lives Golden Ending.
- Clever Town of Salem players can set this up. The Bodyguard protects one person each night, and if that person is attacked, the Bodyguard dies in their place and kills their attacker. The Doctor can heal one person a night, and if that person is attacked, the Doctor will prevent them from dying. If they know each other, they can just heal and protect each other. If the Bodyguard is attacked, the Doctor saves them; if the Doctor is attacked, the Bodyguard will kill their attacker and then be saved by the Doctor. This makes a nigh-invincible duo, and if the evils don't have a way to counter it, this can win Town the game.
- In World of Warcraft, the Demon Hunter opening campaign sets up a situation where a portal needs to be opened, but a soul must be sacrificed to do so. You can choose either to have the person performing the ritual sacrifice himself, or have him sacrifice your character instead. If you choose to let yourself be sacrified, you die and can run back to your corpse (just like any player-character in-game). As a Hand Wave, Illidan communicates with you, letting you know that your character has an immortal demon soul (like Illidan himself, but implied to be rare among other demon hunters), and can't truly be killed outside the Twisting Nether. Your survival amazes the one who performed the ritual.
- At the end of Pillars of Eternity: The White March, a party member has to strike a crystal with a recreation of Abydon's hammer to draw the Eyeless to them, sinking and burying themselves and the Eyeless. There's a number of ways to survive this through earlier decisions, certain items, or sheer physical endurance, but the simplest solution? Have the Devil of Caroc be the one to strike the hammer. She can't drown and can dig herself out of the stones. Thereafter, she will then simply walk to shore.
- Titanfall 2: Near the end of the campaign, BT stays behind to destroy the IMC's Doomsday Device. However, The Stinger implies BT saved himself through his previously used ability to copy himself into the computer in Jack's armor.
- In Schlock Mercenary, while being held prisoner, Kevyn jury-rigs a gravity pulse that takes out the guards, which has the nasty side-effect of killing him as well. Good thing he gate-cloned himself first.
Gav: Does it count as a selfless sacrifice if you clone yourself before your suicide mission?
Kevyn: I'm putting it on my resume and hoping nobody asks.
- This one is a maybe. Gate clones are established to be distinct individuals with identical memories up to the point of cloning, so the original really did die. "Original" in the sense that anyone who had ever used a worm-gate for interstellar travel can still be called that. Basically, before Kevyn invented the teraport, everybody who traveled between solar systems was a Gate clone, the Gate-Keepers were just making an "extra" copy of each person that nobody knew about
- In El Goonish Shive, Elliot, in his superheroine form dives in front of a dragon's fire blast that was otherwise aimed at a busy street. While the ensuing blast and fall from the sky would be enough to kill any normal person several times over, Elliot is durable enough in that form that it merely takes him out of commission for a few minutes.
- In one episode of Batman: The Brave and the Bold, Batman sends an alternate-Earth-destroying bomb as the timer ticks down to the Zombie Earth, after The Reveal that said bomb would only kill instead of causing an Earth-Shattering Kaboom. "Can't be killed."
- Kenny from South Park has done this a few times, since he knows he keeps coming Back from the Dead.
- Well, hard to say; a recent episode makes it sound like he's always known, but whether or not he (or any other character) notices his repeated deaths has usually varied from one episode to another Depending on the Writer and/or depending what would be funniest at the time. Still counts as this trope, though.
- Played with on Avatar: The Last Airbender: Azula shoots lightning at Katara, so Zuko, who's been taught to deflect that attack, jumps in front of her. He still gets massively injured since he didn't have time to do it properly (doesn't exactly mix well with a diving save), but he survives.
- In both the original Captain Scarlet series and the remake, indestructibility is Captain Scarlet's main/only superpower. As such, he tends to pull this off at least once per episode.
- Kaeloo: In the episode "Let's Play Final Days", Kaeloo, Stumpy and Mr. Cat are faced with several objects that are about to kill them, only for Quack Quack to jump in front of them and save them. Quack Quack is completely indestructible.
- Played with on Craig of the Creek, in the episode "You're It". When faced with being exiled from the creek due to a game of tag, Craig gets out it by tagging his older brother, who doesn't care about being unable to go to the creek, since he hates the place.