Mutual Kill

"Now, I don't know who is more metal. The guy who stabbed a man in the face with a three foot long sword. Or the guy who was stabbed in the face, kept walking forward, and still managed to stab the other guy in the chest with three feet of steel jutting out his skull."

- The Dark Id, Let's Play Resident Evil

Two characters commit fatal damage against each other in the same confrontation.

Particularly heart-tugging when it appears the hero has won, it's over... and then they slowly drop to their knees, blood trickling from the side of their mouth. Expect a Big No from the Neutral Female and plenty of protests that "he'll be fine, we can get him to a doctor."

Can happen as a result of the Single Stroke Battle, where both swordsmen inflict a mortal blow on each other, but, usually, one dies instantly, while the other has a moment to philosophically reflect on their demise. It also happens with some Western showdowns, where two gunslingers fatally shoot each other at the same time.

This was Truth in Television, with "ai uchi" (mutual killing -- hence the trope name) being a common outcome of samurai duels. Potentially any duel where weapon inertia or lag can compensate for attack lag can have "mutual killing" as a normal outcome.

Compare Double Knockout, where both combatants inflict critical but non-lethal damage on each other. Similar to, though not quite, Taking You With Me. This is a common, albeit far from guaranteed, result of Deliberate Injury Gambit. May follow a Mexican Standoff. If damage is fatal, but does not prevent immediate retaliation, result may be the same (this includes Time Delayed Death and Incendiary Exponent). Could also be from a Self-Destructive Charge or Poisoned Weapons.

Anime

 * Technically happened in Advent Children: when Cloud defeats Sephiroth, and Kadaj and Cloud make amends before he magically dissipates into thin air, Loz and Yazoo reappear to deliver a mortal gunshot to Cloud. The three explode in a cloud of Mako energy.
 * Spike and Vicious from Cowboy Bebop.
 * Maybe
 * Overlaps with My Name Is Inigo Montoya in the case with Kamina of Tengen Toppa Gurren Lagann: Thymilf deals him mortal wounds, but he decides not to die for long enough to obliterate an army, Thymilf included (inventing a new Finishing Move on the spot), spitting out Arc Words like they were tobacco all the while. Then he basically tells his friends, "I have to go now," and dies.
 * Subverted in the final battle of Samurai Champloo. Jin performs a technique which guarantees this happens as a result of it, but amazingly, he actually manages to survive from the supposedly mortal wound. Even more amusingly, the only thing he does after the recovery is leave the group on friendly terms.
 * Originally, Jin was supposed to die. Then Shinichiro Watanabe chickened out.
 * Inuyasha starts out with this. It's later revealed that Naraku tricked Inu Yasha and Kikyo into killing each other.
 * And even that didn't work. Kikyo decided to seal him instead.
 * In Basilisk, Kouga Gennosuke tries for one of these with Iga-no-Oboro as a final resolution of the Kouga-Iga conflict. However, Oboro refuses to fight him and commits suicide instead. Gennosuke also commits suicide, so the resolution really isn't that far off from a Mutual Kill.
 * The anime also opens with Kouga Danjo and Ogen of the Iga, the grandparents of the two characters above, performing a Mutual Kill. First Danjo inflicts a fatal wound to Ogen, then Ogen backstabs him. First Episode Spoiler and all. Danjo is, mostly, played as the badder of the two, with Ogen receiving a moment or two of pity. Danjo kills Ogen on what appears to be mere SUSPICION that she's part of the contest. Ogen then avenges herself, and has a short moment of reminiscing about their past. They were to be married, as Gennosuke and Oboro were. Danjo's clan, if not Danjo himself, ambushed the Iga fleeing from their village (which was under attack by someone else) in an attempt to wipe them out, ruining the wedding plans. Yeah, it's a really, REALLY sad anime.
 * In ''Naruto Shippuden
 * In the fourth arc of Umineko no Naku Koro Ni, Battler proposes a version of this to explain Kumasawa's, Genji's, and Nanjo's first arc murders. Lambda refutes this during her tea party with Bern.
 * The Lancelot and Guren (but neither of their pilots) in Code Geass.
 * No. It was a Double Knockout where one of the combatants ended up Going Critical and going kaboom due to a lucky hit.
 * Wolfwood and his former mentor in the Trigun anime. The good guy survives long enough to get to a church and decide to NOT light up one last cigarette (honoring a request made earlier by an unrealized love-interest that he stop smoking).
 * In Puella Magi Madoka Magica, Kyouko sacrifices herself to Mercy Kill Sayaka after the later falls to The Corruption.
 * Played straight and averted in Dragonball, with Mu Taito sealing away King Piccolo at the cost of his life. Master Roshi tried the same thing years later, but couldn't pull it off and died for nothing.
 * In the anime version of Sailor Moon, the Sailor Senshi trick Cyprine and Ptilol of the Witches 5 into doing this to each other.
 * Jose and Henrietta in Gunslinger Girl, sort of.
 * In Gantz, both  did this to a boss level alien.

Comic Books

 * Superman and Doomsday, pictured above.
 * G.I. Joe issue 19 (Marvel series) has Kwinn and Dr. Venom kill each other. Kwinn comes to Dr. Venom for revenge while threatening to shove a grenade down his throat. After an exchange of words, Kwinn changes his mind and turns his back on Dr. Venom. His former target then takes the opportunity to shoot him in the back. After Kwinn dies, he drops the grenade which blows Dr. Venom up.
 * Happens in Identity Crisis with Jack Drake and Captain Boomerang. Boomerang would return.
 * The Northlanders story "The Viking Art of Single Combat" is a tale of a trial by combat that, with grim irony, ends in a Mutual Kill.

Film

 * Kerim Bey and the assassin in the film From Russia With Love.
 * Or Was It all done by Red Grant?
 * Robin Williams and Al Pacino's characters at the end of Insomnia.
 * Somewhat averted at the end of Fearless, where Jet Li's character could have created a near simultaneous death of he and his opponent by delivering a fatal blow, but instead only made the motions without delivering lethal force behind the strike.
 * Commodus and Maximus in Gladiator. Commodus stabbed Maximus in the back before their fight to weaken him so he can kill him in the arena... but it didn't weaken Maximus enough, as Maximus kills him before keeling over himself.
 * Ray Liotta and Nestor Carbonell's characters in Smokin Aces.
 * At the end of 300 one of the Spartans gets stabbed with a spear. He then grabs the spear's shaft, pulls it further in order to draw the spearman closer and slashes the poor shmuck.
 * Hanzo and one of the Predators in Predators. It's pretty awesome.
 * Also Nikolai, though in this case it was more Taking You With Me.
 * While not a kill, given who the characters are, the spirit of the trope is invoked in Freddy VS Jason. After Jason runs Freddy through with his own severed arm, Freddy sneers and sinks Jason's machete into his body.
 * During the climax of Exorcist the Beginning Merrin's native guide manages to shoot an angry tribesman at exactly the same time the tribesman throws his spear.
 * In Star Trek Generations, the battle between the Enterprise and a Klingon bird-of-prey results in the destruction of both ships, although the crew of the Enterprise survives.
 * In the Prince of Persia the Sands of Time movie, Seso can throw any blade with surgical precision. He faces off against a Hashanshin firing bolts out of a wrist-mounted automatic crossbow. Seso has one blade left, so he jumps out of the column, runs, aims and throws it, while the Hashanshin is firing bolts at him. The blade flies true and kills the bad guy. Then Seso looks down and sees bolts embedded in his chest. He manages to throw the Dagger of Time off the tower before dying. Luckily, the Reset Button is pushed.
 * Deadman: Nobody and Cole Wilson.
 * Reservoir Dogs has a four-man mutual kill at its climax (or three, as one didn't shoot and was already dying).
 * The beginning of Universal Soldier.
 * At the end of The Grey, Liam Neeson's character is the last one left after the wolves and the Alaskan environment kill off all the other plane crash survivors one-by-one. He finds himself in the middle of the wolves' den (which he thought he was walking away from all this time). In a Bolivian Army Ending, he grabs and knife and some broken bottles and rushes the alpha wolf, who rushes him. The Stinger reveals that they killed each other.

Literature

 * Hamlet and Laertes in a classic example.
 * King Arthur and Mordred.
 * Sherlock Holmes and Moriarty. At least, that was Conan Doyle's idea at first.
 * Rudyard Kipling did something like this in "The King's Ankus", a story in The Second Jungle Book. Several people kill each other to possess the jewelled relic of the title, finishing with a group of men who kill the previous owner, not realising that he's already poisoned their food.
 * The probable inspiration for this was "The Pardoner's Tale" from The Canterbury Tales. Two guys kill one, then drink the drink he'd poisoned before being killed.
 * Several examples in Needful Things by Stephen King.
 * Beowulf and the dragon, though Beowulf had Wiglaf's assistance.
 * Gandalf and the Balrog in The Lord of the Rings, though Gandalf comes right Back From the Dead.
 * Gothmog and Ecthelion in The Silmarillion.
 * And Glorfindel with another unnamed Balrog. This seems to be the only way you're gonna kill one of those things.
 * It's actually a Retcon after the one Gandalf fought ended up being much more powerful then normal. Before, Balrogs were not nearly that powerful and there were as many as a thousand. Later, they were reduced to only about 7 and made much more powerful to compensate. It's noticeable if you read the earlier Drafts, where even a Lowly Man killed at least 3...and without dying.
 * Celegorm and Dior are another example.
 * In the Horatio Hornblower saga, two minor characters died this way during a sea battle, one impaling the other on a sword and getting decapitated in turn. It was referred to as a "two widows' blow".
 * Carrie and Margaret in Carrie. Margaret stabs Carrie and Carrie strikes back, telekinetically giving her mother cardiac arrest. Carrie survives after this exchange long enough to cause Chris Hargensen and Billy Nolan to have a fatal car crash before the combination of shock, blood loss from the knife wound, and overstraining her body finishes her.
 * The movie version has Carrie telekinetically crucifying Margaret in a doorway with assorted kitchen implements after Margaret stabs her. Carrie is then finished off by the burning, collapsing house.
 * The end of the Horus Heresy novel Battle for the Abyss.
 * In Sergey Lukyanenko's Cold Shores, the Church of the Sister sends a paladin and several monks to escort Ilmar to Urbis (this world's Vatican). They are intercepted by a party of monks of the Church of the Redeemer, also headed by a paladin. The two parties kill each other, while Ilmar slips away. One paladin manages to crack the other's skull, while the other one was swinging his nunchucks; then the nunchucks connected and mortally wounded the first paladin.
 * In Babylon Five: The Passing of the Techno-Mages, Galen's parents kill each other. Prior to that, his mother gave a ring to his father as a gift, which was a trap that electrocuted the guy. While he was convulsing, though, he managed to hurl several fireballs at her.
 * The Redwall series has quite a few examples of this, both hero-vs-villain and villain-vs-villain. Examples: . A villain-vs-villain example would be between
 * In the Iron Druid Chronicles Thor manages to smash Leif's head in with his hammer but not before Leif cut him with a magical sword that kills anyone it wounds.
 * In The Saga of the Noble Dead, the elves Sgaile and Hkuan'duv kill each other in a fight at the end of Child of a Dead God.
 * In Memory Sorrow and Thorn, the "pulling yourself up the sword that's impaling you to kill its wielder" version is pulled off by the Norns defending Naglimund.
 * Mentioned in a Backstory anecdote from Priest-Kings of Gor. Two men from different cities went on a Quest and were to each other as brothers. After the quest was over they returned to their cities; the cities later went to war with each other and the two men killed each other on the field of battle.

Live Action TV

 * Londo and G'Kar in Babylon Five.
 * There is also a battle between a Centauri and a Narn warships, resulting in one ship being blown up and the other one receiving critical damage and exploding a few seconds later.
 * This trope is a favorite of CSI where a dead guy will lead to another character who was wounded in the altercation and is similarly dying (or else becoming severely harmed/handicapped).
 * One episode of Psych has 2 spouses murder each other, with the first poisoning the 2nd before they were killed, and the 2nd taking a more direct approach. Lassiter is not amused that Shawn called him when there was no one alive to arrest.
 * Ben and Justin end up doing this to each other at the end of the last season of Carnivale, however both survive due to avataric healing powers.
 * Darkonda and Dark Specter in Countdown to Destruction.
 * This appears to happen in the season 1 finale of Earth Final Conflict with Boone and Ha'Gel, who both fire energy blasts at each other. Ha'Gel is disintegrated, and Boone is heavily wounded. Subverted in that he would have survived if Zo'or had not disintegrated him while in the healing tank.
 * Also, Ha'Gel is an Energy Being and later comes back to talk to his son Liam Kincaid.
 * Happens twice in Legend of the Seeker. In Richard's nightmarish vision of a Bad Future, Cara does a Face Heel Turn, forcing Kahlan to kill her. Before dying, though, she touches her Agiel to Kahlan's chest, killing her as well. In the season 2 finale, Kahlan herself is confessed by Nicci and flies into a "blood rage" when Nicci is wounded. She remotely confesses four Mord-Sith and orders them to kill each other. They do so by touching each other's hearts with the Agiel simultaneously.
 * On Justified Raylan almost convinced two criminals to drop their guns and surrender to him when they realize that only one of them will be able to make a deal for immunity and the other will go to prison for a long time. They turn on each other and before Raylan can stop them, they shoot each other. One dies instantly and the other sustains a fatal wound.

Music

 * Percy French's Abdul Abulbul Amir ends with both Abdul and his opponent Ivan Skavinsky Skavar fatally wounding each other.

Myth And Legend

 * King Arthur and Mordred. 'Nuff said.
 * In Norse Mythology, pretty much all the Norse gods bow out this way at Ragnarok: Loki and Heimdall, Jormungand and Thor, and Garm and Tyr. (Odin fails to kill Fenris, but is avenged by his son.)
 * In Greek Mythology, Oedipus's sons, Polyneices and Eteocles, killed each other. King Creon's prohibition of the former's burial due to him turning his back on the kingdom would set up the plot of Antigone.

Tabletop Games

 * Can happen if two units with the same Initiative score go toe-to-toe in Warhammer 40000. One battle report ended with an Inquisitor Lord and a 13th Company Rune Priest simultaneously smashing each other flat, for example.
 * Possible in Battle Tech, as damage is dealt simultaneously, so a mech or tank that's been killed still has the chance to fire back and get a possible kill in return. Especially likely if both units are heavily damaged.
 * Can happen in Exalted where combat actions are determined by ticks. if two characters are due to act in the same tick both their actions happen simultaneously and damage and effect caused by the other character take affect only after that characters turn. that way both characters can kill each other at the same time.

Theatre

 * Hamlet and Laertes. Hamlet survives just long enough to take final vengeance upon Claudius before dying from being poisoned by Laertes' sword.
 * The climax of Death Trap, play and movie.

Video Games

 * Pretty common in multiplayer FPSs (Wolf Team especially). If there are any slower-than-instantaneous weapons in the game, mutual kills are bound to happen.
 * Team Fortress 2 has several possibilites:
 * The Pyro can set enemies on fire, which causes DPS. This means that it's possible for someone to die from the burning even after they killed the Pyro. The Pyro update includes two achievements for killing enemies this way.
 * It's also possible to do the same with Bleeding, which a few melee weapons can induce.
 * The WAR update also gave the Soldier an achievement for killing a Sniper with a rocket after he kills you, aptly named Mutually Assured Destruction.
 * In turn, the Sniper can kill an enemy with the Huntsman after he's already dead. This also rewards the Dead Reckoning achievement.
 * Can happen to classes with splash damage weapons. If you're playing as Soldier, are badly wounded and fire on your attacker point blank, you can expect a shower of both your chunks. Can also happen with Demomen, and Engineers if they're foolish enough to stand between an enemy and their own turret.
 * Rocket launchers are especially guilty of this in Quake III Arena, Open Arena and practically any game which has them, as well as mines and grenades in Battlefield 1942.
 * Halo 3 has a multiplayer medal for anyone who does this, usually by tossing a grenade right before death.
 * Also common is where two players run at each other guns blazing, depleting their shields, but running out of ammo, then both do a melee attack, causing both to be sent flying back, dead.
 * The Needler is also good at causing these because of the delay between impact and damage.
 * It is also possible for two players to hit each other with a plasma grenade, causing them to blow themselves up.
 * Emile in Halo Reach does this with a Zealot after being impaled by its energy sword.
 * Can occur in World of Warcraft regarding Warlocks. Warlocks are able to cast many spells which cause damage over time, and remain after the caster's death. A common complaint against warlocks regarding PVP was that, in a duel to the death between you and a Warlock, you'd always die even if the warlock dies first (the fact that he might be able to resurrect himself afterwards didn't help).
 * While Warlocks are the most prominent class when it comes to damage over time, pretty much any class (and many mobs) can use damage over time effects and potentially get the same outcome. Shadow Priests, Death Knights and Balance Druids immediately come to mind.
 * Can also occur in the traditional fashion, often due to lag. Also, some boss encounters have special conditions that the group needs to look out for that can last longer than the actual fight. It's not uncommon for people to forget about it while rushing to the boss to check what he drops, and depending on what the respective effect is, they can accidentally blow up half the raid by doing so.
 * In this troper's experience, at least, it's fairly common for hunters to mutual kill one another in PVP.
 * After making a Heel Face Turn, Gamma in Sonic Adventure decides that he has to "save" the rest of the E-100 Series (That is to say, destroy them, saving the little animals inside). When he defeats the last one, his brother Beta, Beta gives him one last dying attack, that causes the both of them to be destroyed.
 * In Real Time Strategy games, it is always possible to call in massive ordnance danger close, when expecting that your units won't survive the current engagement. In World in Conflict, for example, online players often decide to not withdraw the ground units before overwhelming enemy forces, summon an airstrike (which takes some time to arrive), and let the enemy pummel them to death -- only to get hit by the bombs the moment they finish off the last defender. Sometimes, players call in the airstrike too early, killing their remaining units themselves and making it a Taking You With Me instead.
 * The nature of tactical aids in the game makes this tactic borderline essential, since it's hard to hit moving opponents and they might even suspect one to be incoming if the enemy gives up too soon.
 * In Shogun: Total War, attempting to kill a geisha with another geisha results in a cutscene that shows them having a tea ceremony before grabbing their swords and slashing each other. A moment later, both are lying in pools of blood. The strikes themselves are not shown, as the camera is zoomed in to the tea set before pulling back to reveal the bodies.
 * An infantry battle described in the manual of the third Wing Commander game over a totally worthless planet ended with the last surviving Confederation platoon overrunning the last Kilrathi position, with the survivors lasting just long enough to report their victory before dying themselves.
 * Goldeneye64 has a one hit kill multiplayer mode, which can often lead to this. It even has an award called "double kill", and the much more rare "triple kill".
 * In Master of Orion, when a ship is destroyed, its warp drive has a high probability of exploding violently, damaging any ship in the vicinity. It is thus possible to destroy an enemy ship and then have your own ship be destroyed by the warp wave. A technology can be obtained a number of ways (but not through research) allowing a ship's drive to be specially rigged to blow up even more spectacularly, dealing triple damage. The same can happen when a ship is ordered to self-destruct.
 * In the 4X game Starbase Orion for i Phone (a clone of Master of Orion), it is possible for two ships to kill each other if they're close in strength, especially with long-range weapons which take time to travel. This is because weapons always hit in this game (unless intercepted by point-defense systems).

Web comics

 * K'seliss in Goblins, having lost both of his arms to an Eldritch Abomination that spreads a flesh-rotting curse through touch, kills the abomination with a bite that tears through its neck. This results in the curse spreading to the rest of his body and dissolving him.

Web Original

 * Happens occasionally in Survival of the Fittest, one particularly notable example being the fight between Cassandra Roivas and Kiyoko Asakawa.
 * Also related are Gail Smith vs. Sera Wingfield and Will Sigurbjornsson vs. Stephanie Evans.
 * And now we can add Holly Chapman and Johnny Marsh of the spinoff Evolution. Before this, this was how Cristo Ruiz and Otis Adelaide died.
 * Alex White and Jimmy Brennan also die this way in v4, after a rather brutal confrontation.
 * Played for laughs here. "Did you hit brain?" "A little."
 * Occurs in Season 6 Episode 5 of Mindcrack Mindcrack Server Ultra Hardcore when Pause and Nebris manage to stab each other at the exact same moment when both were already near death.

Western Animation

 * Depth Charge and Rampage in Beast Wars. Depth Charge got the last laugh... he was resurrected in the Universe comics.
 * Although it was less that they wounded each other than that Rampage exploded when he got stabbed.
 * Likewise, Optimus Primal spends most of the last episode of Beast Machines getting owned by Megatron, but manages to turn the tables by plunging Megs into the "organic core" of Cybertron while he's holding Optimus, killing both of them.
 * Unusual twist: former allies turned enemies Demona and Macbeth from Gargoyles are both immortal and will simply return to life no matter how they "die" unless one kills the other, which will cause them both to die.
 * Demona takes advantage of this to remain essentially immortal, Macbeth on the other hand has dedicated the last century or so to tracking her down and killing her so he can finally have peace.
 * Played straight with the Captain and Hakon, who pushed each other off a cliff.
 * Optimus Prime and Megatron in Transformers the Movie. Prime died of his wounds, and Megatron was chucked out the airlock in a shockingly Genre Blind move by Starscream before he could die of his.
 * Although Megatron was too weak to resist Starscream and arguably could have died if his wounds weren't treated.
 * Also, the two boombox transformers Blaster and Soundwave engage in a duel in the first episode of Transformers Headmasters, resulting in Soundwave exploding and Blaster dying from fatal wounds. Both are later rebuilt as Twincast and Soundblast, respectively, with different color schemes.
 * The Disney Villain Death in The Secret of NIMH.
 * In the 1939 MGM animated short Peace On Earth, this is how the last two human beings on Earth kill each other, leaving the Earth to be populated by sentient Ridiculously Cute Critters.
 * The Flight of Dragons has Sir Orrin Neville-Smythe being bombarded with fire by Bryagh, with zero protection save for his full plate armor. Throwing his sword, he manages to penetrate Bryagh's bellyscales, forcing him to keel over from the sudden explosion of fire within him, and Sir Orrin himself succumbs immediately afterwards.

Real Life

 * A traditional risk of boar-hunting, and the reason boar spears are designed with a cross-piece. If not stopped, the boar may run itself up the spear and gore you before it dies.
 * Firearm users refer to a weapon's stopping power, or ability to put a hostile down. It is very easy for a projectile to cause a lethal wound but still allow an individual to act for a few seconds, letting them shoot or charge and stab the user. Stopping power is the ability to put a target down, whether or not the wound is lethal.
 * This is the theory of Mutually Assured Destruction. Second strike capacity is defensive in nature; it ensures that any kill will be a mutual kill and (hopefully) scares the enemy into not attacking. A missile shield of some sort would, in the perverse logic of nuclear arms, actually allow an attack.
 * This can easily happen using most hand weapons. Most weapons, when wielded, inherently create an opening when used to attack. For example, someone using a rapier in a lunge is vulnerable to a counter-attack. The lunging swordsman would defend against this by either by having an off-hand parrying implement or assuming their opponent wants to live and will defend rather than simply counter-attack into the lunge. Japanese swordsmanship is perhaps the only style of make a virtue of cutting your enemy down as he does you. Since sword-fighting occurred before modern medicine, there were all kinds of lethal but not instantly-incapacitating wounds like punctured lungs or punctured bowels. Then there's head trauma, which can cause sudden death hours after "recovery."