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Anime & Manga
- Bleach: The filler Bount arc features Dolls, the Bounts' Empathic Weapon. Similar to Zanpakutō, but the Bount and Doll are more linked; if one dies, so does the other.
- Sailor Moon: If the Maijuku dies, Al and En go down as well. Or as En's dub counterpart explains, "if the Tree dies, ALAN, we die!"
- Fai and Kurogane in Tsubasa -RESERVoir CHRoNiCLE-; the former can't live without the latter, since, as a vampire, Fai's dependent on blood for feeding, and can only feed on Kurogane.
- Arthur and Shalott in Air Gear; Shalott was almost killed when another character kicked through his chest, damaging all his vital organs, so Arthur's organs were transplanted into Shalott. Now Arthur has no organs, so he's dependent on a literal blood connection between him and Shalott for feeding and waste elimination, and will die in a couple hours if the connection is interrupted.
- Elraine and Kiri of Double Arts, must always be physically touching (normally holding hands) or Elraine will die of the disease she's infected with but he's immune to and staves off.
- Charlie in Vassalord is a vampire who is dependent on blood from his master Rayflo because, due to Charlie's religious views, he refuses to drink from humans since he sees it as a cardinal sin. (Drinking from Rayflo is also a sin, but in Charlie's eyes it's the lesser of two evils.)
- In Katekyō Hitman Reborn!, one character, Chrome Dokuro can live only because her organs, the originals of which have been removed, are physical illusions cast by Mukuro Rokudo.
- In one chapter of Black Jack, the title doctor surgically attaches a young boy with lungs weakened by heart disease to his mother until he can get an organ donor.
- Ah! My Goddess has the doublet system, in which random pairs from heaven and hell are linked. If one dies, the other dies. After they are linked, their memories are erased — the purpose being so if you kill someone on the other side, you don't know which of your allies would die (it could be you, natch).
- Dragon Ball Z: If Piccolo were to die, then Kami would as well and vice-versa. This is because they were originally one person but Kami cast off his evilness in order to become guardian of Earth. That evilness turned into Piccolo. On the plus side, you only have to resurrect one to get both back. This is no longer an issue once the two of them fuse back into one being.
- Shenron and Porunga also cease to exist (and their respective Dragon Balls turn to stone) if their creator dies. For Shenron, that's Kami, later replaced by Dende after Kami fuses with Piccolo. For Porunga, that's Grand Elder Guru, later replaced by Elder Moori after Guru passes away.
- Similarly, in Dragon Ball Super, it's revealed that if the Supreme Kai were to die, so would Beerus. The reverse is, presumably, true. Goku surmises that he could defeat the latter if he defeated the former, but then decides that wouldn't be any fun. Beerus is less than amused.
- Whis also cannot exist without a God of Destruction around, so if Beerus dies, Whis will cease to function until someone else takes up the role. This is probably why he asked Goku and Vegeta if they wanted to replace Beerus if he dies, as a backup plan for it it happens.
- Sequence, by Saenagi Ryou, starts out with the main character, Kanata, accidentally freeing a young imprisoned vampire, and getting his heart ripped out for his trouble. The vampire, who isn't actually a bad person, ties their life forces together to keep Kanata alive.
- This is the case for Eureka in the Eureka Seven movie ending when she was reborn as a human being. She stated that she could only exist as long as Renton lives and dreams.
- In The World God Only Knows, Elsie and Keima share collars/chokers that dictate that if one dies, the other will as well, no matter what they die from.
- InuYasha: According to Naraku's final detachment Byakuya, even if his other "siblings" had survived, they would have perished if/when Naraku was destroyed anyway.
- Fairy Tail: Since the Books of Zeref channel their creator's magic, if Zeref were to die, the Etherious will die with him. This includes E.N.D., which is why Happy prevents Natsu from landing a possible finishing blow on his brother/creator after learning the truth of his origins.
- In the Marvel Universe, villainous duo Hammer and Anvil were linked by an alien device that gave them superpowers but also linked their life force. When one was shot in the head, the other also died.
- Cloak & Dagger of the same universe depend on each other a little less dramatically — without the countervailing influence of the other's powers, each would go (respectively) terminally depressive or destructively manic from the effect of their own.
- In Being Dead Ain't Easy, Yami Bakura reveals that since Kaiba bonded Joey's soul to his own, Joey has been slowly killing Kaiba as his own condition worsens.
Films — Animation
- In Tangled, Gothel is dependent on Rapunzel's magical hair to keep her perpetually young; without it, she will rapidly age until death.
Films — Live-Action
- In Battle Royale II the students are paired up so that if one of them dies the exploding collar of their partner also goes off.
- In Dragonheart, a dragon can bestow part of its heart on a person, making him immortal — so long as the dragon lives.
- In Star Wars continuity, the Tusken Raiders of Tattoine ride giant, shaggy beasts called banthas, which are bonded to their owners via a combination of training and affinity. If a bantha's rider dies, the bantha usually dies shortly after, often becoming feral and violent before dying.
- In Dragonriders of Pern, the dragons are symbiotes who literally can't face life without their rider: a dragon who fails to find a compatible rider upon hatching will die. If they bond to a rider and the rider dies, the psychological trauma causes the dragon to cross the Despair Event Horizon and commit suicide. The only exception is a queen dragon whose rider dies while the dragon is waiting for eggs to hatch — she'll wait until just before Hatching to go Between, and in the intervening time she won't leave her eggs, even to feed herself.
- The riders don't fare much better if their dragons die. One rider went Between with the above-mentioned queen dragon since the queen dragon's rider was riding the first rider's dragon (an older queen dragon) and they made the fatal mistake of going Between when they were already exhausted from doing so multiple times. Other riders in the series have been reduced to a child-like state (Kylara) or have been driven insane with rage (T'Kul). Going through the rest of their lives as shadows of their former selves devoting themselves to other causes to remain sane (Lytol and Brekke) is the best case scenario.
- In Howl's Moving Castle by Diana Wynne Jones (and the film of the book by Hayao Miyazaki), a magical contract binds Howl and Calcifer together. So, as is often referenced when Calcifer talks to Sophie, "If I die, Howl dies too."
- Inverted in Harry Potter, as the prophecy in the fifth books points out, "Neither can live while the other survives." However, you could say that it is played straight, as Harry is an unintentional horcrux. When Voldemort kills him, he seals his own death.
- The Wheel of Time: Aes Sedai and their Warders have a Downplayed version of this bond. If a Warder kicks it, the Aes Sedai will be hit with pretty fierce depression, occasionally bordering on suicidal. Warders who lose their Aes Sedai generally go whole hog, becoming Death Seekers against either the person who killed their partner or just whatever's at hand. It's very, very difficult to keep a surviving Warder alive, and it almost always requires extreme measures.
- Inverted in Percy Jackson and the Olympians: Instead of a person being dependent on an object, it's the other way around — the Labyrinth can't survive without Daedalus.
- Due to plot complications involving the source of his agelessness, the eponymous protagonist of the German pulp series Professor Zamorra has recently (as of this writing) become dependent on his friend Rhett Saris not so much to stay alive as to keep his youth; without him, he would revert to his actual chronological age, which while not actually enough to kill him — the series hasn't run quite that long yet — probably would force him to retire from fighting the various forces of evil. (This is complicated by the fact that Rhett himself might yet end up turning into a fairly major demon himself if one of Hell's long-term plans is ever allowed to reach fruition...and they both know it.)
- In the Honor Harrington novels, it is common for bonded treecats to suicide after their human partner, or treecat romantic partner, dies. Since the natural lifespan of a treecat is considerably longer than that of a (pre-prolong) human, the bonding pretty much meant that bonding with a human meant that the treecat would sacrifice many decades of their lifespan. It is also stated that a human whose 'cat dies is likely to give up on their own life as well.
- Humans and their daemons in His Dark Materials. A slight variation, in that it is possible to separate a daemon from their human with specialist equipment. In this case, both survive, but both are reduced to shadows of their former selves, as the daemon represents the human's soul. Separating them by any other means is fatal to both.
- The Maternity Spell in the Sword of Truth series does this as part of its synchronization effect. It links the caster and the target such that whatever physically happens to one happens to the other — if the caster is punched in the nose, the target gets a nosebleed. So if the caster is killed...
- In Watersong, there must always be four sirens, and they must always remain close to one another. If one of the sirens spends more than a few weeks away from the others, or if a siren dies without being replaced by the next full moon, all will perish.
- In the first Neogicia novel, Saly, the protagonist undergoes Bio-Augmentation and wakes up with a second level of consciousness that seems to have developped to avoid sensory overload. In the second, it turns out to be actually be an entity using her as host body, which fills very specific critera seldom found in the general population. That entity is ready to go to lengths much greater that what Saly would consider acceptable to keep her alive and can take over in an emergency. The fact Saly it does sensory overload prevention in Saly even when dormant creates an downplayed mutual need.
- Stargate SG-1:
- The Jaffa race in the Stargate-verse have been genetically engineered such that their immune systems shut down at puberty. As such, they can't live for long without having a Goa'uld larva inside their pouch, until a medicine that has the same effect is discovered in one of the later seasons.
- In one story arc, Daniel and Vala put on bracelets that create a link between them, so that to be any more than a few feet away from each other can cause them extreme physical discomfort and eventually death.
- Star Trek:
- The same thing happens to Picard and Dr. Crusher on Star Trek: The Next Generation, except it is an implant. It also makes them able to read the other's thoughts.
- The Trill and their symbionts in the Star Trek Verse: they share knowledge, and Trills can live just fine without a symbiote, but if a symbiote implanted in a Trill is removed the process invariably proves to be fatal to the host. Though the removal is not instantly fatal, nor the bonding instantly permanent. In one episode, a non-joined Trill hijacks the Dax symbiote from Jadzia and joins with it. Sisko recognizes the new Dax, but, when the Trill refuses to relinquish the symbiote, Sisko tells him their friendship is over, since it will eventually mean Jadzia's death. Eventually, Jadzia recovers Dax and the other Trill is brought to justice.
- Star Trek seems to love this one. The Bynars are a race of cyborgs who always live and work in pairs and can't function alone.
- Farscape used synchronizing bracelets for a few episodes involving negotiations.
Myths & Religion
- This trope was intentionally invoked in the now-rare Hindu practice of sati — when a man died, his wife burned herself to death on his funeral pyre.
- Truth in Television for some cultures — Yanomamo rainforest Indians believe that everybody has a kind of animal doppelgänger called a noreshi, which takes the form of aerial or arboreal animals for men or ground-dwelling animals for women. They say that to kill one's noreshi would cause the person drop dead and vice versa. Many intentionally try to find their rivals' noreshi for this reason, as outright murder is a pretty damn stupid idea in a culture where inter-village alliances are about as sturdy as damp tissue.
- The Greek myth of Meleager involves a woman giving birth to a son, but she overheard the Fates saying that his life was linked to a piece of wood in the fireplace (already burned halfway through). She quickly took it out and extinguished it, saving his life. Years later, the son got in an argument with his maternal uncle and killed him... Fwoosh.
- Dungeons & Dragons:
- Some races in D&D have their Life Force linked to an item, plant or place, mostly nature spirits or descendants of some such, with direct inspiration from folklore or mythology. Nereids carry a shawl that contains their soul, and someone seizing it and threatening to destroy it can control the creature. Dryads and Hamadryads are linked to a single tree in the forest. Bamboo and River Spirit Folks, from the Oriental Adventures, are synchronized with a specific bamboo grove or river, respectively. Damaging a linked tree or place will weaken or wound those spirits, and destroying it will kill them.
- 4th Edition has an entire race built on this — the Dvati, a species consisting completely of identical twins, with "souls that burn so brightly one body is not enough to contain them". They don't share damage exactly, but are played as one character (with their HP divided in half between two bodies) and have some limitations on what both can do in one round. If one Dvati twin dies, the other takes unhealable ability damage from the shock and loss of the other half of their soul until either they die too or the other twin is raised/resurrected.
- In BioShock 2 it is revealed that if an Alpha Model Big Daddy (the Player Character in the second game, different from the Big Daddies encountered in the first game) is too far away from his Little Sister, he either dies or lapses into a coma.
- Dragon Age: Origins: Wynne is dependent on a friendly Fade spirit to keep her alive.
- In the second Zone of the Enders game, the protagonist Dingo is critically injured and linked to Jehuty so he can live, at the expense of not being able to survive outside of Jehuty.
- Similar but opposite to Pern cycle, the Bond in Drakan series connects the dragon and his rider in such way that if the dragon dies, so does the rider, but not vice-versa (justified by the fact that dragons are just that much more powerful). Arokh, for example, has outlived at least one rider already.
- In Enslaved: Odyssey to the West, the player character is forcibly bonded to a Damsel in Distress Gadgeteer Genius via a Restraining Bolt that will crush his skull if he disobeys her or she dies, because she can't survive in the killbot-infested wasteland on their own.
- In Knights Of The Old Republic II The Sith Lord, the player character and his mentor Kreia are linked by a Force Bond, gaining each other strengths and weaknesses. This isn't exactly convenient - in particular, the player is made aware of the bond when Kreia loses a hand fighting the apparent Big Bad Darth Sion to keep him at bay, and the player character half the ship away at this point immediately recoils in pain as if their hand got lopped off - so getting rid of it is one of the major plot points. In the end, when Kreia turns out to be The Man Behind the Man, she uses this as the player character's incentive to follow her to the final planet in the game - if they try to run or hide, Kreia will kill herself and thus also kill the PC no matter where they may be.
- In Final Fantasy IV, the death of a summoned monster results in the death of the Summoner. This is how Rydia's mother dies early in the game. Once it returns to the realm of summoned monsters, the Summoner can no longer be harmed by its death. Which is likely why Rydia always has her monsters show up for a single attack and then teleport away.
- In the ending for Tales of Destiny 2, Reala dies along with the final boss Elraine when Kyle destroys the huge lens, as it is the only way to ensure the demise of Elraine, much to the dismay of Kyle. Although in the restarted timeline, thanks to The Power of Love, Reala is miraculously reborn and reunited with Kyle at the place where they met for the first time.
- Alcatraz in Crysis 2 is only kept alive by the Nanosuit, and even then, just barely. At a couple of points in the game the player has to use the suit's defibrillator system to revive him. Though the suit ends up being less of a life support system and more of a symbiote over the course of the game.
- Late in Kid Icarus: Uprising Dark Pit discovers that if anything serious happens to Pit, he's affected by it too, and makes keeping Pit alive his top priority.
- In the Dead Money DLC of Fallout: New Vegas, Elijah links the Explosive Leashes of you and your companions so that you don't try and betray each other.
- In The World Ends with You, if a Player is erased, their partner is as well in seven minutes unless they make a new pact with a different denizen of the Underground.
- Prominent in the Nasuverse. In the Tsukihime sequel Kagetsu Tohya, it's revealed that when the magus who created a familiar dies, the familiar will also die. The only exceptions are when it is a very advanced creation such as Len, who is still dying because of it. For the same reason (mana sustaining their life) Servants in Fate/stay night will quickly die without a Master. However, this isn't an entirely straight example as the person in question can be replaced... but it is still a replacement in a dependency situation.
- In the 8th arc of Umineko: When They Cry, it's stated in red text that if Shannon dies, Kanon will disappear for all eternity. This is because Shannon and Kanon are actually the same person, Sayo "Yasu" Yasuda.
- In Girl Genius Martellus tries to control Agatha this way. He changes her body's chemistry so that she needs to be around him to survive. If he dies so does she. Agatha gets around this by applying whatever he did to himself to a wasp eater. Although she still needs one of them near to live, she is no longer dependent solely on Martellus.
- All of the Ghost/Spirit pairs in Guardian Ghost are this, where if anything happens to break their link (like the ghost half of the pair getting destroyed) then the Spirit dies instantly as their soul gets wiped out.
- In Mystery Babylon, Kick Girl and Kill Boy share the same soul; if one of them is killed, the other will die as well. This doesn't stop Kill Boy from attempting to kill her anyway, as he bears a huge grudge against her and isn't afraid of dying.
- In Use Sword on Monster the main character defeats a mage from another dimension. Believing he intends to torture her, she casts a spell on him that makes whatever hurt her hurt him as well (in her own dimension, the spell was used to punish Domestic Abuse). For the rest of the story the two are dependent on each other for survival.
- Code Lyoko: Although Aelita is materialized in the second season, XANA ensured the kids can't Cut the Juice on him by linking Aelita to the Supercomputer. She lapses into unconsciousness whenever the machine is turned off — and a too long interruption will make her heart stop.
- After Fry is critically injured in a car crash in Futurama, his head is attached to Amy's body to make sure he survives until his body is healed.
- Likewise to the above Futurama entry, in a "Treehouse of Horror" episode of The Simpsons, Mr. Burns' head was attached to Homer's body.
- In one episode of Ben 10, Ben and Kevin are captured and forced into Gladiator Games. They are shackled together by an energy shackle so that if one dies, the other does too.
- In one episode of The Marvelous Misadventures of Flapjack, K'Nuckles angers off a plague rat who Flapjack befriends. All of Stormalong Harbor contracts the Plague, and Flapjack thinks he is the cause, so he sails away to plague island to live the rest of his life. A boat with K'nuckles and many other citizens show up, and he tells Flapjack that they can't live without him. Flap thinks it's a sentimental statement, but then K'nuckles clarifies that they literally can't live without him. His blood contains the antidote.
- Wakfu: The whole Sadida people is linked with the Tree of Life, a huge sentient tree at the heart of their kingdom. This prove a lethal weakness when Nox decides to drain the wakfu of the Tree of Life, and thus of every Sadida alive.
- This, along with traits of Synchronization, is the case between Demona and Macbeth in Gargoyles.
- Max and Steel in the rebooted version of Max Steel. Without Max, Steel will run out of power and shut down for good. Without Steel, Max would basically explode.
- Invoked in a thought experiment brought up about the abortion debate, where you are asked to be connected to a concert pianist or rocket scientist for nine months because they need your blood supply to live. Pregnancy itself is also an example for the developing fetus.
- Biological examples:
- Mitochondria in eukaryotic cells — that is, cells with a nucleus — and chloroplasts in plants started as independent proto- and cyano- bacteria which survived being enveloped by these larger cells and became symbiotic. They have co-evolved to the point where both mitochondria and chloroplasts are considered organelles, and essential ones at that.
- Many flowering plants rely heavily on insects in the process of breeding.
- Most large plants can build a highly beneficial symbiotic link with fungus. However, some plants literally cannot live without one.
- Lichens are another example of a tight symbiotic link. They consist of a fungus and a photosynthetic partner.
- Humans are an example as well. The human body is the host of a large amount of microflora. Most of it is located in the digestive system, but the skin and most mucous membranes normally have microflora as well. Removing these residents may result in problems with digestion or vulnerabilities to some diseases, which must be considered when the doctor decides to give you antibiotic treatment.
- Legions of parasitic lifeforms cannot survive without a host. Different forms of symbiosis, ranging from straight parasitism to closely linked true symbiosis, are very common in nature.
- Certain nastier forms of plasmids have developed addiction systems to keep them safe inside their hosts. Basically, the plasmid produces a toxin that will kill its host, as well as an antidote to that toxin that degrades faster. If the plasmid is removed, the toxin will kill the host once the antidote degrades beyond usefulness.