History Main / OnlyOneMeAllowedRightNow

* ''VideoGame/PuyoPuyo'' has a universal law where only one unique character is allowed to exist in a given world. If another tries to occupy that spot, the weaker of the two will undergo CessationOfExistence. Normally, this isn't a problem as the three worlds explored are all heavily distinct from each other in setting and cast, but Doppelganger Arle makes this everyone's problem in ''VideoGame/PuyoPuyon'', where she's heavily aware of this universal rule and creates a plan to [[KillAndReplace lure and kill Arle so she can take her place within their current setting]]. She fails and is ultimately casted out, but the ''[[AllThereInTheManual Drama CD #5]]'' story "Time Space Travel Tour" revealed she was able to survive by hiding out in a CloseEnoughTimeline.

* In ''Series/MirrorMirror'', things that exist at both times are prevented from crossing the mirror: If you try to take one with you, you'll be shocked instead.
* ''Series/TheAdventuresOfBriscoCountyJr''' zig-zags this, albeit probably unintentionally. In one epsisode Brisco goes back in time and gets an Orb from his past self, telling himself that he needs it in the future. In a later episode Brisco goes back in time again to effect a BigDamnHeroes moment that went badly the first time around, but this time his past self disappears from the continuum when he does so.
* An alternate reality example in ''Series/EarthFinalConflict''. When Liam and Augur accidentally end up in a parallel world, where humanity is fighting a losing war against the Taelons, they manage to flee back to their own reality with Maiya, a member of LaResistance and Lili's half-sister. On their world, though, Maiya starts experiencing an effect similar to the one in ''Series/StargateSG1'', cause by the presence of her double Isabel. They are told that they must "merge" into one in order to survive. This world's Lili also discovers that her missing father had another family, and that Isabel is her half-sister. When Isabel and Maiya come close, they merge into one body, but, unfortunately, Isabel's personality is gone, leaving only Maiya.

* An explicit absolute in the [[https://www.goodreads.com/series/45571-agent-of-t-e-r-r-a Agent of T.E.R.R.A.]] by Larry Maddox. Hannibal Fortune is a time traveling trouble-shooter for the [[https://tvtropes.org/pmwiki/pmwiki.php/Main/FunWithAcronyms Temporal Entropy Restructure and Repair Agency]], which attempts to fix all of the problems caused by the the time traveling bad guys of Empire. At one point he is in the middle of a battle (which he is losing), and he jumps into his time machine and travels to his home time. He then takes a long nap, because he knows he will be able to take years or longer to plan and prepare for his return at one micro-second past the time he left. Further, he can go back to years before the battle and plant tools and weapons for his use, because he hadn't visited that time previously.

* An explicit absolute in the [[Agent of T.E.R.R.A. https://www.goodreads.com/series/45571-agent-of-t-e-r-r-a]] by Larry Maddox. Hannibal Fortune is a time traveling trouble-shooter for the [[https://tvtropes.org/pmwiki/pmwiki.php/Main/FunWithAcronyms Temporal Entropy Restructure and Repair Agency]], which attempts to fix all of the problems caused by the the time traveling bad guys of Empire. At one point he is in the middle of a battle (which he is losing), and he jumps into his time machine and travels to his home time. He then takes a long nap, because he knows he will be able to take years or longer to plan and prepare for his return at one micro-second past the time he left. Further, he can go back to years before the battle and plant tools and weapons for his use, because he hadn't visited that time previously.

* In ''Fanfic/GeorgeWeasleyAndTheComputationalError'', the universe normally works like this, with some exceptions like twins and Time-Turner users. Unfortunately for the universe, it's bad at counting so if someone with an already existing duplicate comes from the far future, it won't take action (that is, eject the time traveler from the universe) unless they call attention to themselves.

SubTrope of OurClonesAreDifferent. [[CaptainObvious Interestingly enough, this doesn't happen in RealLife.]]

* This happened to Comicbook/JubileeMarvelComics in an issue of ''Comicbook/{{Wolverine}}'': In her youth, there was an incident where she was in a car with her friends, who suddenly asked her why she momentarily disappeared into thin air. Not remembering doing so, she dismisses it as her friends acting crazy. Years later, she briefly falls into the time portal belonging to Gateway, appearing in her parents' house, at the exact same time she "disappeared" in her friends' car. It is explained that two of her couldn't exist in the same point in time, so her younger self simply vanished until the older version returned to the present.
* Normally, time travel doesn't exactly work in the Franchise/MarvelUniverse. If you travel into the past, you end up in the past of a similar but distinct universe (which you might not be able to distinguish at the time). For example, when ComicBook/RachelSummers (daughter of ComicBook/JeanGrey and [[ComicBook/{{Cyclops}} Scott Summers]]) traveled into the past, she ended up in the primary universe instead of the offshoot where she was born (where Jean Grey was depowered instead of killed). She didn't realize she wasn't in her own timeline until she saw Jean Grey (well, actually Madelyn Pryor, but close enough) and Scott Summers had a son... she never had a brother.

* Normally, time travel doesn't exactly work in the Franchise/MarvelUniverse. If you travel into the past, you end up in the past of a similar but distinct universe (which you might not be able to distinguish at the time). For example, when ComicBook/RachelSummers (daughter of ComicBook/JeanGrey and [[ComicBook/{{Cyclops}} Scott Summers]]) traveled into the past, she ended up in the primary universe instead of the offshoot where she was born (where Jean Grey was depowered instead of killed). She didn't realize she wasn't in her own timeline until she saw Jean Grey (well, actually Madelyn Pryor, but [[CloningBlues close enough]]) and Scott Summers had a son... she never had a brother.

Note that this is NOT NeverTheSelvesShallMeet. In that one, you can have millions of copies of a same character running around in the same universe without that much trouble, only they must not meet each other. In this case, even though there are only two copies and they are at opposite ends of the Universe, the problem still happens. Not as tightly related to the OneSteveLimit as you might think.

* In Creator/DeanKoontz's Lightning, the inventors of time traveling discover that the universe has a built-in anti-paradox mechanism, where you simply get bounced back from the time-gate if you are attempting to travel to a time where you're already present (or even might be - one character tries to correct a mistake by traveling to a time a couple of minutes before he last showed up, and the universe doesn't let him).

* In Creator/PiersAnthony's Literature/IncarnationsOfImmortality, the rule is, instead, that only three of a person is allowed to exist simultaneously. This mostly comes up in ''Literature/BearingAnHourglass'', as the current Chronos is living concurrently with himself, but backwards, which means he is only allowed to travel to a particular point in his life once and once only.

* Creator/IsaacAsimov and Creator/JanetAsimov's ''Literature/TheNorbyChronicles'': In this setting, you cannot travel to a time where you already exist, although how the universe resolves that [[TimeyWimeyBall tends to vary]]. Norby cannot travel to a time where he already exists, but he can take passengers along with him. ''Literature/NorbysOtherSecret'' establishes that if one of the passengers already exists at that time, that passenger would disappear, and would only reappear when he travelled to a time where they don’t currently exist. ''Literature/NorbyAndTheQueensNecklace'' establishes the necklace device, which tries to merge with other copies of itself (including Norby). When they first use the necklace, the past version wriggles towards Albany, who is wearing the present version, so that the two can become one object again.

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* In ''WesternAnimation/JusticeLeague'', Vandal Savage's time machine cannot send a person back to when that person existed. Since he's an [[{{Immortality}} immortal]] who's lived through around 99% of human history this means he can't actually use it himself. In his first appearance, this did not prevent him from sending a recording and ''information'' back into time. In his third, in "Hereafter", [[spoiler:he's the sole human survivor of a distant future, AfterTheEnd (entirely his fault and he knows it), and when he's finally joined by a Superman who got bumped forward 30,000 years, they eventually realize that Superman is "already dead" and the chance is there for him to go back and prevent Savage's attack from happening]].
* ''{{WesternAnimation/Futurama}}: Bender's Big Score'' has this in effect. Whenever a duplicate is created through time travel, the universe eventually kills them off to prevent further confusion. However, at the end of the movie, several hundred time-traveling Benders appear simultaneously; this proves too much for the universe to handle, and a hole in space-time rips open.

* In ''Series/SevenDays'' when Parker goes back in time, the Parker from the time he goes back to disappears from existence (as does the time machine itself and anything else inside it).

* In ''VideoGame/MortalKombat11'', timeline shenanigans occur thanks to the BigBad and causes characters from the past appearing in the present time. The multiple copies are allowed to exist except for Raiden. Due to a law from the Elder Gods stating that there can never be more than one of them existing at any time, the Raiden of the present [[RetGone ceases to exist]] while the Raiden of the past takes his place. No one sees this as a bad thing since the vanished Raiden had become a KnightTemplar and the heroes disliked his change.