Can't Live Without You

Maybe you've been put through an Emergency Transformation; maybe a magic spell backfired in an epic fashion; maybe someone decided it would be fun to mess with your life (you know, For Science!); or maybe it's just the way things work in The 'Verse you're currently a denizen of. Any way it went down, you are now literally physically dependent on something (or someone) else for your continued existence. You get bonus points if your counterpart is also dependent on you, but this often is not the case.

If the link also transmits feelings, pain or injury, this trope overlaps with Synchronization.

For cases where the link isn't vital for either part but simply beneficial, see The Symbiote.

This trope is not about people who can't stand to live apart from each other but are still physically able to do so; for those, head over to either Living Emotional Crutch or If I Can't Have You…. Compare Shared Life Energy. See also Soul Jar when it also gives a form of immortality. Also note that this is unrelated to Can't Live with Them, Can't Live Without Them.

Contrast Gemini Destruction Law.

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Examples:

• Anime & Manga
• Fan Works
• Literature
• Video Games

Comic Books

• 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 and 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.

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.
• The titular Pumpkinhead is a demonic entity brought forth to wreak vengeance on those who wronged the summoner, and the only way to put it down before it completes the task is to kill the one who summoned it.
• 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.

Live-Action TV

• Farscape used synchronizing bracelets for a few episodes involving negotiations.
• Lost Love in Times: Qing Chen links her life with Yuan Ling's to stop him killing her. When she cuts her finger, his finger starts bleeding too. When he's poisoned, the poison affects her too.
• Mako Mermaids: An H₂O Adventure: All natural-born mermaids depend on their Moon Pool's well-being for their survival. If a Moon Pool is drained of its magic or destroyed, the mermaids connected to it will die along with it. This caveat does not apply to humans-turned-mermaids.
• Once Upon a Time:
  • Season 5's last two episodes introduce Dr. Jekyll and Mr. Hyde, with Jekyll finally completing a serum that splits he and Hyde into two separate bodies. Regina also uses it to divide herself from the Evil Queen, intending to kill her other half. However, it eventually comes out that the serum wasn't perfect — when the original person is killed, their other half will die as well (as seen when Hyde dies after Jekyll is impaled). It's inverted when the second person is killed — Regina crushes the Evil Queen's heart, but she revives because Regina is still alive. The Evil Queen ultimately obtains the Shears of Destiny to completely separate the two, but Regina ends up using a method that lets the pair co-exist as separate individuals, neither completely good nor evil.
  • In season 7, the Wish Realm's version of Rumplestiltskin is bound to the original version of him this way — when the original Rumple performs a Heroic Sacrifice and dies permanently, Wish Realm Rumple (the last villain standing of the series) disintegrates.
• Red Dwarf: The episode "Entangled" reveals this to be the case for Rimmer and Lister; if Lister dies, Rimmer's hologram is shut off in response.
• 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. Teal'c explains they were originally created to be worn by a Jaffa guard escorting a prisoner, the illness and death meant to ensure that the prisoner couldn't escape. When asked why it made both wearers sick, Teal'c replies that was to punish the guard for letting the prisoner escape in the first place.
• 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.

Myths & Religion

• 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.
• 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.

Tabletop Games

• Dungeons & Dragons:
  • Some races in D&D have their Life Energy 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.
  • Originating from 2nd Edition, there is 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.

Visual Novels

• 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.

Web Original

• Double Life SMP: It overlaps with Synchronization as the premise of the season. Each player's health-bar is linked to another as "soulmates"; if one takes damage so will the other, and if one dies, the other does as well.
• Empires SMP Season 1: A prophecy in the ancient Elven library says this about the Champions of Aeor and Exor, saying that "One cannot exist without the other, for if one soul dies, the other is sure to follow." Scott eventually exploits this in the season finale as the then-Champion of Aeor; when Xornoth — then-Champion of Exor — breaks out of his Crystal Prison during the Apocalypse How, captures him, and threatens to force him watch his friends and loved ones get tortured to death, Scott uses the Rune Blade to take down Xornoth once and for all... by taking himself out of the equation.

Webcomics

• 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.
  • Later another character suffers the same problem. Turns out the chemistry alteration is a two-way street and now Martellus will die without Agatha's touch and unlike her he has no alternative.
• 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.

Western Animation

• 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.
• Centaurworld has The Nowhere King and the General. Originally an elktaur who separated himself into his human and elk halves to be with a princess he fell in love with (a.k.a. The Mysterious Woman), the human half went on to become the General and marry the Woman while the elk half was forced to live in the woods and scavenge or steal what normal food he could. When the General tried to drown the Elk after the Elk threatened to expose the truth, the General only relented when he learned—by way of choking on the same water that was drowning the Elk—that killing the Elk meant killing himself. Instead, he imprisoned the Elk in a windowless cell too small to even stand in for ten years. This, combined with despair from never seeing the Woman again and having nowhere to belong, would lead to him becoming The Nowhere King.
• 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.
• Gargoyles: While Demona and Macbeth have Resurrective Immortality against every thing else, were one of them to kill the other, both would die.
• The Fairly Oddparents: Both inverted and played straight. The existence of all fairies and their respective anti-fairies are linked 1:1. If one is born, the other will be born shortly after, as shown when baby Poof's birth leads to Foop being born as well. And if one dies, the other will die shortly after, when Foop's plan to erase Poof erases himself as well, at least until the both of them are rescued from the limbo of Hocus Poconos. After that happens, Foop's hatred of Poof goes from a desire to eliminate down to a mere rivalry, since he now knows firsthand that any real danger he puts Poof in will go both ways.
• In Futurama, after Fry is critically injured in a car crash, 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 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.
• 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.
• In Steven Universe, Steven's Gem is essentially his life force. After it was forcefully removed by White Diamond, it forms a Hard Light body of its own while his organic body turns pale and becomes weak to the point he can't stand and can barely talk, requiring Connie's help to reunite with his Gem.
• 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.

Real Life

• Invoked in a thought experiment (Judith Jarvis Thompson's violinist experiment, if you want to google it) brought up about the abortion debate, where the society of music lovers kidnaps you to be connected to a genius violinist for nine months because they need your blood supply to live. How analogous this is to an actual pregnancy is a contested matter.
• Pregnancy itself is 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.
• Conjoined twins that happen to share a vital organ usually do not have the option to be separated, lest one or both of them end up dying as a result.

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