In a realm beyond sight The sky shines gold, not blue There, the Triforce's might Makes mortal dreams come true.
"Who designed this campaign setting? Why would you include four points of such catastrophic weakness that tampering with any of them results in the destruction of the global ecosystem? It makes no sense! A kind and loving creator would never have done this, and a cruel one would simply have made the air out of acid. And it wouldn't have evolved on its own, as there's no advantage to living in a world poised on the brink of annihilation!"
Kisuke Urahara describes the Soul King as this. Without him, everything will fall apart. Aizen isn't happy about this logic.
In Digimon Adventure 02, the Digital World has seven Destiny Stones which maintain the barriers between realities. Each universe seems to have equivalents, our world's being Kyoto shrines. If all of any one universe's set of seven are destroyed, all dimensions will collide, destroying the multiverse. You'd think The Four Gods would have thought twice about leaving them all in plain sight and in the same city.
In X/1999, the world will essentially end if seven buildings in Tokyo are destroyed. Naturally, the Dragons of Earth tend to challenge the Dragons of Heaven to massive, destructive battles at these places.
In the Pokémon 2000 movie, three of the Legendary Birds maintained the balance of the world's climates. Capturing just one quickly threw the whole thing out of whack, turning a tropical area downright arctic. This is a massive change of theme from the Gotta Catch Them All mindset of the games; More like "Catch 'em all... except these three!" It's unknown whether this applies just to those specific three, or whether the capture of ANY Legendary Bird would have the same effect (or whether it would make a difference if the Bird went willingly).
When Ash meets one of the Frontier Brains, him and the others tell the Brain how impressive it is that he caught Articuno (although he didn't), showing that, at the very least, one CAN catch the birds as long as they aren't from the three islands. Either that, or Ash suffered from amnesia after that movie.
Considering the fact that later tournaments have competors packing Full Legendariesi.e. Heatran, Latios, and Darkrai, and this isn't the first appearance of the lastnote nor of the others if you count the Movies (and time travel for the first), it seems that the former is the case. Granted, however, the events in Pokémon Diamond and Pearl mentioned in the Video Game section below also occurred in the Animenote as did the Ruby-Sapphire one, to anextent; making this a case of "depending on the Legendary."
In Mahou Sensei Negima!, the Magical World has literal Keys that can rewrite reality. The villains already have a few of these Keys, and used them to erase several Magical World inhabitants from existence including Jack Rakan. Obtaining the most powerful Key of them all is the main goal of the villains and the heroes (who want to undo the damage already inflicted by the villains).
The plot of Magic Knight Rayearth revolves around saving the kidnapped "Pillar of Cephiro", who supports the existence of the entire world with her prayers. The plot of Rayearth 2 revolves around finding a new Pillar.
In Spider Riders the Oracle Keys where created to... Well we don't know exactly why they exist, except to tempt people into abuseing there power.
Transformers Cybertron revolved around the characters attempting to recover the Cyber Planet Keys and the Omega Lock. Optimus Prime needed them to save Cybertron, Starscream wanted to become a god, and Megatron wanted to destroy the universe and remake it in his image.
The Marvel Universe contains several objects capable of severely screwing up time and space, some of which bestow varying degrees of omnipotence on their wielders. These include the Infinity Gems (particularly when brought together and mounted in the Infinity Gauntlet), the M'Kraan Crystal, and the Ultimate Nullifier. One of the very first such artifacts was the Cosmic Cube, now made famous by the Avengers' film.
Most of the gods (and we mean Cosmic gods, not the local ones like Thor) are this as well, which is why they can't just kill Galactus or a Celestial. It's eventually shown exactly why killing Galactus would be a very bad thing, when somebody manages to actually do it: the Nigh OmnipotentOmnicidal Maniac Abraxas is unleashed. Galactus gets restored to life afterward.
The relationship between Cyclops and Jean Grey, of all things. Certain things with universe-affecting implications (such as stopping the M'Kraan Crystal, as mentioned above) don't happen if Scott and Jean never got together.
In Bone, the Crown of Horns is the balancing point of both the physical world and the dreaming-world.
Nowadays in the DC Universe, the whole of the multiverse (fifty one universes to be exact) rest on top of the main Universe-0 (the fifty-second), more specifically on Earth due to all of the massive Crisis Crossovers. Should Earth-0 ever be destroyed, all of the multiverse would be destroyed (this was the goal of the Anti-Monitor in the Sinestro Corps War arc).
In the limited series "Trinity", the Big Three (Superman, Batman, and Wonder Woman) are cosmic keystones of the cosmic keystone earth.
Eclipso once tried to destroy Earth as part of its plan to kill Godbecause Earth itself is vital to God. Earth was created by God to be the wellspring of belief that fuels His continued existence.
In the Buffy the Vampire Slayer Season Eight comics, the Seed of the World, the source of all magic in this reality, is introduced. It was in the custody of the resurrected Master until it was recovered and destroyed. Season Nine reveals that the Seed was the source of creativity as well. Unless it is somehow replaced, humanity will lose their stories, music, and art forever.
Subverted in Death: The High Cost of Living. Some of the characters, and likely also the reader, believe that the ankh that Death carries around holds some cosmic power. It doesn't. It's just an affectation. When the Eremite steals it, Death just...buys another one.
Films — Animated
Subverted in The Thief and the Cobbler, in which an Opening Monologue explains that the safety and balance of the Golden City depends on three golden balls perched on top of a minaret. News of an invading army comes just as King Nod discovers that the balls are gone, but the defeat of said army only seems to be incidental to the Thief finding and "returning" them.
Films — Live-Action
In Dogma, the cosmic keystone isn't an object, but a concept: God is Infallible. If God is ever proven wrong, existence would end. The movie's plot involves stopping two angels from doing that, by using Hollywood Catholic Dogma to end their banishment on earth.
The Fifth Element didn't just have cosmic keystones, but a living "perfect" human, the titular Fifth Element, was the focus and trigger for the only weapon that could fend off the elemental, perfect evil that wanted to destroy the world.
Smaller-scale version in Sgt. Pepper's Lonely Hearts Club Band with the original band's instruments, which protect the Sugar Bowl of Heartland USA. When they're stolen and scattered, the town decays into a sleazy shadow of its original self.
White gold in The Chronicles of Thomas Covenant is a cosmic keystone that is conveniently located outside of the cosmos it affects... until the start of the story anyway. The One Tree is another cosmic keystone, but with protections far surpassing the typical keystone. (Subverts the usual pattern further in that the Dark Lord never got his hands on them — they were used by the good guys instead.)
Well, not really. The Big Bad DOES get his hands on the white gold at the end of the Second trilogy. At that point, however, the hero has realized the true nature of the power of the white gold, and is able to trick the Big Bad into wasting his one shot at its use.
The white gold itself isn't precisely a Cosmic Keystone; it's just a way to draw power from the real Cosmic Keystone, the Arch of Time. If the white gold is destroyed, nothing happens. If the Arch of Time is destroyed, reality (if you can call it that) will crumble.
The Dark Tower in the series of the same name. It manifests in all worlds, but only in one does it appear as an actual tower — which is held up by six radiating Beams that span the sky in twelve directions from it. In most worlds, it takes the form of a rose, though it has also been known to appear as a tiger, a dog, or a talisman. One might question how a structure that is supposed to be the sustainer, or container, of all space-time can be threatened from inside the passage of time, but, you know, whatever.
According to Roland's palaver with the man in black at the end of the first book, there are infinite universes, and each one is a mere fundamental particle inside another, which is a mere fundamental particle inside another, ad infinitum. Each fundamental particle in each universe also contains another universe, and so on, forever and ever. Since each universe contains a physical manifestation of the Tower, that means that, as you expand beyond the billions of universes that your own is stacked inside (like Russian dolls), you're eventually going to discover that your own universe is a fundamental particle inside another universe's version of the Tower. Meaning that if the Tower gets destroyed, all of the infinite universes get destroyed too... because they're all, ultimately, within an infinite number of different versions of it. For example, Mid-World is inside a fundamental particle in the rose in Keystone Earth. The Tower is inside an infinite number of itself, it contains an infinite number of itself, each universe contains an infinite number of universes and is contained within an infinite number of other universes... everything is connected, and the destruction of one Cosmic Keystone is all it takes to bring everything down.
In an interesting twist, two entire universes function as Cosmic Keystones for The Multiverse. One the world in which the Tower exists as a real tower, and most of the characters' adventures take place. The other is (almost) our world, in which their adventures are described in a series of books by Stephen King — actually referred to as the "Keystone World", and the only one for which time travel is impossible. Destroying the Tower in either of these universes would lead to all of God's (er, "Gan's") creation being unraveled.
One fascinating aspect of The Dark Tower series is its metafictional nature. The many fictional universes that were created by Stephen King are explicitly stated to revolve around the Tower, and it's directly implied that other fictional universes, including the Marvel Universe, the Star Wars universe, and the Harry Potter universe, are also connected to the Tower. The broader implication is that EVERY fictional universe is connected to King's creation, that the creator gods referred to in fictional works are ALL different aspects of Gan, the god of The Dark Tower, and that the Tower itself has a manifestation in EVERY fictional Verse. For example, by King's logic, the One-Above-All who appears in the Marvel comics would be an aspect of Gan, and the Triforce would be Zelda universe's manifestation of the Tower.
The Boxes of Orden in the Sword of Truth series fit the trope, as using them incorrectly can let the Keeper, the local equivalent of Satan, into the world of the living. The Pillars of Creation are living versions.
The Holy Grail Lightstone is the Cosmic Keystone of the Ea Cycle. One would think something with that level of potential for abuse would have been guarded better.
The Young Wizards series has The Book of Night with Moon, a book which describes the entirety of existence and which must be read from periodically by wizards in order to remind Reality what it's supposed to be like. It's indestructible and can't be used by the Big Bad, but simply keeping it out of the hands of the good guys for long enough will result in reality slowly unraveling.
Played sort of straight in Robert Jordan's The Wheel of Time series with the 'invincible' cuendillar seals containing The Dark One being the key to his release and the apocalypse that would ensue as he rewrote the Pattern in his image.
Interestingly, Jordan plays with this trope as the seals are gradually weakening (and outright breaking in some cases) without any outside influence. This is generally put down to The Dark One breaking free of his prison, because the seals are the focus of the magic that's doing the actual imprisoning, so although they're invincible normally, as the magic gets damaged so do they.
At the end of the series, Rand realizes that the Dark One itself is also a keystone of sorts. It, and by extension evil itself, is vital to humanity's capacity for choice and change. People need to be able to make poor choices.
Ray Feist'sThe Riftwar Cycle, and most particularly A Darkness at Sethanon, has the Lifestone, which draws power from and could be used to end all life on the planet. Justified as the creators thereof didn't give a good goddamn if they sterilized the planet so long as they won their war. They didn't.
The Orb of Aldur and the Sardion in the Belgariad and the Malloreon are stones which embody the conflicting destinies of the universe and bestow godlike power on anyone they allow to hold them.
The Ruby Sunstone was said to be something like this for Dinotopia in 'First Flight'; it would maintain a balance as long as it stayed in its place at Highnest, but trouble would ensure if it was removed. However, it may have simply been a legend or First Flight may not completely fit into the other books' canon, as the Sunstone was lost, then stolen briefly by Lee Crabb, then dropped into the sea during the final battle where Arthur and Will, helped by the Skybax,Northies and Giganotosaurs, managed to stop him.
The TV miniseries came up with a storyline about a ring of sunstones that kept the large carnivores in the basin, when some of them went out, chaos ensued.
The 1978-1979 series of Doctor Who revolved around the Doctor's needing to gather and assemble the pieces of "The Key to Time", scattered across space and time, before an evil power could get its hands on it. The villain had a particularly clever plot, too; his agent located the final piece of the Key and settled down nearby to wait for the Doctor to bring all the other pieces there along with him when he came for it.
Subverted somewhat in that The Key To Time is used to restore the universe's balance, which apparently gets upset all the time. This is partly because the opposing Black and White Guardians of Time are adversaries, and keeping the pieces of the key scattered is necessary to prevent the Black Guardian (Chaos) in particular from using it to spread entropy.
The new series also features an equation that can "solve" the universe, and somehow rewrite it to suit the solver's needs. The Doctor has to decide whether or not to use it to bring back the Time Lords and stop the Time War from happening. Hedidn't.
'Logopolis', the final Tom Baker episode, features the titular planet which was itself a universal keystone. The people were bringing energy into the universe as a way to fight off entropy. When the Master decides to stop activity there for a little while (admittedly, not really understanding what they were doing) large chunks of reality were destroyed before the problem could be fixed. Even then, there was no reset button.
Gallifrey itself may be full of these, not least of which are The Eye of Harmony and The Moment. It is taken quite seriously that the Time Lords could end the universe if they chose to do so, using technology they already possess.
In Season 5 of Buffy, we get "The Key" (note the capital K), a device which can destroy the barrier between realities and turn southern California into Hell on Earth.
Done in a slightly harder SF context in seaQuest DSV. A deforested future Earth depends on ten massive air processing plants to keep what's left of the planet livable. Then a race of genetically engineered Super Soldiers - with lower oxygen requirements - decide they wouldn't mind the place to themselves...
Pro Pinball: Timeshock! has Time Crystals, which are needed to generate a counter-shockwave of time to prevent the end of reality.
The Tesseract in The Avengers (Stern), which spells COSMIC (and enables the Super Jackpot) as it spins.
Religion and Mythology
One interpretation of the biblical story of Adam and Eve holds that the Forbidden Fruit of the tree of knowledge essentially acted as a Cosmic Keystone. The serpent, who is supposed to representSatan, tricks them into partaking of the forbidden fruit. The result, of course, is the fall of man and the ruin of God's perfect creation. Some believe that this is the reason why we have natural disasters, diseases, wars, famine, and death in the world today.
Interestingly, Revelation 5-6 and 8:1 speak of a scroll that is believed by scholars to be the title deed to the Earth. Now to whom could it belong? It's Jesus.
In Greek Mythology, anyone who burns the entrails of the Ophiotaurus would gain the power to defeat the gods.
In many fantasy RPGs is a common plot device used by Game Masters. Have the heroes find the Cosmic Keystone before the Big Bad can get to it and destroy it. Very much a form of stock plot.
Used very literally in the Dungeons & Dragons adventure module The Apocalypse Stone. The Stone of Corbinet (which must always be italicised) is the Cosmic Keystone used by the gods to create whichever world you choose to set the campaign in, and which connects it to the other planes. As long as it stays in Castle Pescheour, the Axis Mundi, everything's fine. The castle is watched over and kept secret by the Pescheour family and their servants. The Big Bad is an exiled prince of the family whose brother was chosen to rule the castle in his stead, and who doesn't even know what the Stone really does, but wants to steal it so he can play king himself. He sets the player characters to steal it in his stead with no idea what they're actually doing. As the world starts to fall apart gradually as a result and the heroes eventually find out what they've done, they must hurry to undo their mistake — the Big Bad certainly isn't going to that, being evil enough to let the world be reduced to nothing if he can't have his way with things.
Exalted has a few examples, most notably the Elemental Poles and the Loom of Fate. Differ from most in that the Poles are incredibly durable and malleable (the four that exist at the edge of the world can adjust themselves to how far the edge happens to be), and the Loom is probably the best defended thing in the world.
The Pillars of Nosgoth in Blood Omen: Legacy of Kain, though there it's subverted because the Anti-Hero protagonist decides to destroy the pillars completely and rule as an evil vampire king.
The Pillars are technically more of a representation of the state of Nosgoth as a whole, and they are maintained by their nine guardians, whose states of mind the pillars reflect. Alternatively, the player can choose to save the pillars by killing himself (him being, unknowlingly, the last pillar guardian), but canon says that he chose not to, condemning the pillars to eternal ruination.
Later games reveal that Kain killing himself would have doomed Nosgoth anyway. As the last true vampire, Kain's existence is connected to the Pillars since they were originally created by the vampires prior to their corruption. This makes Kain himself a Cosmic Keystone.
The original has the Four Orbs, one for each classical element. Their loss is what's slowly destroying the world. They were only called "Orbs" because "Crystals" wouldn't fit in the space allotted.
Final Fantasy III (the real one) had four elemental crystals, fairly standard stuff. Much like the elemental crystals of Final Fantasy V (see below), they give the heroes jobs. Unusually, they are neither destroyed, stolen, nor tampered with. They are losing their light, though, which is why the Wind Crystal summons the Onion Kids (or Luneth in the remake.)
Final Fantasy IV had not just four crystals for the elements, but an additional four dark equivalents for the underworld. While these crystals are never threatened within the time-frame of the game (merely used as tools to reach villains' goals), it is strongly implied that they are just as vital to the world as similar crystals other installments in the series.
And there's a second full set of eight on the Moon. Using both sets together is what enabled the Big Bad to send the Giant of Bab-il down to the world in order to raze it.
Final Fantasy V also had four crystals for the elements, the destruction of each in turn wreaking havoc with the given element.
Final Fantasy VI had the statues of the three goddesses, which merely moving out of alignment would cause the entire world to fall to pieces. Although they have that effect because they want to destroy the world, or at least don't care if it gets wrecked while they fight amongst themselves.
According to the Esper legend, the Warring Triad came to realize the horror they had brought upon the world, and voluntarily sealed themselves away. However, the raw magic that emanates from them is so powerful, they need to be sealed in a precise alignment to nullify each other, and prevent their mere existence from causing further damage.
Final Fantasy Mystic Quest had four Crystals very similar to the Orbs in the first Final Fantasy. Additionally, there was a Crystal of Light, but its significance to the world was never well-established.
In something of a reversal, Final Fantasy Tactics Advance had the protagonist going around destroying Ivalice's Cosmic Keystone set to turn the world back to normal. This is subverted when, after all of the keystones are destroyed, nothing changes - the world is still held together by Mewt's desire to live there, and the only way to unravel it is to convince him to give it up.
In Final Fantasy IX, the Crystal is indeed a very Cosmic Keystone, as all life, everywhere, comes from and is sustained by it.
It's very much like that as well in Final Fantasy XI, as the Mothercrystal is the basis for all of Vana'diel. It was also absurdly hard to get to, originally, but when the thing trying to destroy it is comic itself, that kinda doesn't matter.
In Final Fantasy XIII, the Cocoon Fal'Cie Orphan is the keystone that holds Cocoon together. Without it, all of Cocoon's Fal'Cie would die and Cocoon along with them. The Fal'Cie want this to happen. They miss their creator and hate working for humans that much.
In Ocarina of Time, Ganondorf makes a grab for the Triforce (whole) and it shatters: Power is given to Ganondorf, Wisdom goes to Zelda, and Courage goes to Link. The real Ganondorf has been with Power in almost every other game (A Link to the Past is a notable exception since the Triforce is actually all in one place for once), while Link is often on quests to retrieve Courage and Zelda almost always has Wisdom innately (with the original game being exception for both).
Which in turn explains his incessant desire to kill or otherwise "deal with" Link and Zelda, since the death of either will release their part of the Triforce, making it up for grabs — exactly what Ganondorf wants.
The Legend of Zelda: Twilight Princess changes up the mythos a bit: the Triforce is notably backgrounded, and new Light Spirits are added; without the Light Spirits, the Twilight Realm takes over the world. And the Twilight Realm has its own — small suns that return Dark creatures to their original, more peaceful forms.
The endgame of A Link Between Worlds shows just how powerful the Triforce is: The people of the Alternate Dimension of Lorule destroyed their Triforce to prevent abuse of its power, only to find that it literally acted as a keystone holding everything together and that without it the world was doomed to slow destruction. Link and Zelda then wish on the Hyrulean Triforce, and it creates a replacement Lorulean Triforce.
Tales of Symphonia has the Mana Tree, which has already been dead for four thousand years or so due to a great Magitek-based war. Mithos made a Sadistic Choice and split the world in two, then set up a system to sustain both worlds with what little mana came from the Mana Tree seed; but then he started obsessing over reviving his sister, necessitating a Screw Destiny by the heroes.
The Mana Tree's revived by the end of the game... only for it to die again in another Magitek war in the backstory to Tales of Phantasia. Derris-Kharlan's Mana Tree also died in the backstory, prompting Dhaos to come to Aselia to procure a Mana Tree seed to save his world. He gets his wish in the end, albeit posthumously.
Romancing SaGa pulls something more out of this, The legendary Artifacts; Fatestones, if not collected will be used to power up the Final Boss, you can even power him up intentionally for a greater challenge if you wish after clearing the game one time.
In Star Fox Adventures, General Scales manages to snag the four SpellStones that keep the planet together. Its initial effect is to push four chunks of land away from the planet, but there are concerns that the planet could explode. You don't need to worry about that happening, however; you can Take Your Time.
In Valkyrie Profile 2 Silmeria, the four worlds of the setting are each stabilized by one of the four treasures. Removing a treasure from its world causes that world to quickly become unstable and eventually cease existing.
The world of Wizardry VI, VII & VIII are chucked full of these. First theres the Cosmic Forge, a pen and book in which anything written (or erased) affects reality accordingly.
The four seals in Drakengard fill this role. Partially subverted in that the world was created far differently from how it appears, and the seals hold back the true world by replacing it with one that is user-friendly.
In Zork: Grand Inquisitor, the world will stay a world oppressed by the technological dictator The Grand Inqisitor if the player doesn't find three object with massive magical power: a Cube of Foundation, the Skull of Yoruk, and the Coconut of Quendor.
In Nox, the player must find the Halberd of Horrendous, the Heart of Nox, the Weirdling, and finally The Orb.
In Diablo II, the evil Baal tries to capture the Worldstone. He aims to corrupt it and turn the mortal world into a bastion of Hell. He pretty much succeeds. Tyrael is forced to destroy the Worldstone to keep Sanctuary from becoming part of Hell. Fortunately, destroying the Worldstone removes the seal on humanity's true potential as angel-demon hybrids (Sanctuary itself was created through an angel-demon union). Unfortunately, it also makes humanity a target for the fanatically anti-demon angels.
Diablo III has another, the Crystal Arch, which is the origin of all Angels and their power. If it is destroyed, Angeldom will cease to exist and both Sanctuary and the High Heavens will be cast into darkness forever. Diablo is just barely prevented from doing this.
Golden Sun features the Elemental Stars, which when removed from their hidden chamber cause a calamitous volcanic eruption. Placing these stars in their respective elemental lighthouses will destroy the world. But in Golden Sun: The Lost Age, this is inverted: If the Elemental Lighthouses are not lit, the world will definitely be destroyed, and the only danger otherwise comes from what humans might do with the power of the activated lighthouses. Oh, and just lighting a few of the Lighthouses will upset the climate. Case in point: the Mercury Lighthouse stopped the excessive snowing in the Imil region (and may have stopped the rain on the Osenia continent), the Venus Lighthouse caused a massive earthquake and tidal wave, and slammed Indra into Osenia and Gondowan, and the combination of both Mercury and Jupiter being lit with only Venus to counter them dropped the world's temperature. Things only stabilized after the Mars Lighthouse was lit.
The Elder Scrolls IV: Oblivion: Inverted in that the player goes around entering small hellish dimensions stealing their cosmic keystones in order to collapse them and prevent the demons within from attacking your world. Of course, the reason the demons are able to do open up the portals is because the Cosmic Keystone on your side (The Amulet of Kings) was stolen, and you need to get it back.
The Elder Scrolls III: Morrowind features the heart of Lorkhan, who is also the creator of Mundus and Nirn, in which the TES series takes place. Additionally, after having powered the massive golem Numidium once, the golem breaks reality each time it is turned on.
It's buried fairly deep in the lore, but the events of Oblivion were actually set in motion by the destruction of disguised cosmic keystones across Nirn, including the Heart of Lorkhan. With enough of them gone, Mundus is in trouble; this also suggests that Azura's motivations in steering the hero towards destroying the heart in Morrowind may have been out of different motivations than she let on.
Oblivion revolves around three cosmic keystones: the Emperor's bloodline, the Amulet of Kings, and the Dragonfires. The Dragonfires maintain the barrier that separates Mundus from the (other?) Daedric Realms as long as they remain lit. They were created through a bloodpact between the Emperor's ancestor and the leader of the Aedra, the dragon god Akatosh. Due to this, the fires only remain lit so long as the current Emperor is still alive; if the Emperor dies, another of the bloodline must relight the fires using the Amulet of Kings (which holds Akatosh's own blood) or else the barrier weakens and eventually vanishes. By the end of the main campaign all three keystones are lost. Mehrunes Dagon shatters the barrier and enters Mundus, rendering the Dragonfires useless. Martin Septim, the last member of the Emperor's bloodline, shatters the Amulet of Kings and sacrifices himself to become an avatar of Akatosh in order to fight off the Daedra Prince of Destruction. Dagon is sent back to Oblivion, but the dragon avatar is mortally wounded as well and turns into a statue that replaces the Dragonfires.
The Elder Scrolls V: Skyrim Features this as part of its backstory. According to the faiths of most elves, Mundus(their physical universe) is a prison for their souls. Several prominant landmarks in the series, The Crystal Tower, The White-Gold Tower, and Red Mountain, were part of a series of things holding it all together. The reason that the Thalmor(the fascist High Elf political group) forced the Empire to ban Talos worship is because they believe that is the only thing keeping reality from collapsing.
Averted/Inverted in Suikoden, with it's 27 True Runes. The Runes are major parts of the world, and at least one is required for the continued existence of its domain (the Dragon Rune allows dragons to exist) and the destruction of the 5 True Elemental Runes is Not A Good Thing. In fact, it's implied (and the Big Bad of Suikoden III's plan is predicated on this premise) that the destruction of any one of the True Runes would destroy the world. However, the Runes are rarely in danger as they have wills of their own and generally control their bearer far more than their bearers control them.
And even if the bearer has sufficient willpower to dominate the Rune, the Rune will never have sufficient power to destroy itself or any of the other Runes. To destroy a True Rune requires multiple other Runes' powers to be united, under very specific circumstances. And even then, it's not certain that the attempt to destroy the True Wind Rune would actually have worked even if it hadn't been interrupted.
Pokémon Ruby and Sapphire/Emerald were centered around this. Evil bad guy(s) steal(s) object(s) of power, world goes to hell.
Pokémon Diamond and Pearl/Platinum were even more centered around the trope, if that's even possible. There were even separate levels of Cosmic Keystones here: the Lake Trio, when brought together, created the Red Chain. That in turn summoned Dialga or Palkia, who were cosmic lynchpins that could literally destroy and reform the universe. Platinum takes it a step further, with the temporospatial chaos created by Dialga and Palkia's presence summoning Giratina, who could also destroy the world. Presumably with a bigger bang. And, wouldn't you know, Cyrus had the fantastic idea to make the Red Chain and (try to) pull this Trope, though it turned out to be pretty difficult.
Another D/P example is found in the postgame, when the removal of the Magma Stone from Stark Mountain almost caused said volcano to erupt. Not "cosmic" persay, but certainly destructive.
The Time Gears in Pokemon Mystery Dungeon Explorers are initially believed to be responsible for maintaining the flow of time in the world, but in reality, are simply tools needed to repair the true keystone; the Temporal Tower.
The first Ty the Tasmanian Tiger has five talismans that need to be recovered so the Big Bad of the series can't unlock the power of the Dreamtime and wipe out all the mammals. Incidentally, the place the talismans are returned to serves as the conveniently-located hub of the game.
Wild ARMs has the Tear Drop - a crystal with a link to the guardians and should not be in the wrong hands. There's also the Ray Line, a sort of underground conduit linking the guardians' powers. When the villains manage to damage it, the forces of nature go out of whack, wreaking havoc.
In Mother 3, the Seven Needles sealing away the Dark Dragon, although subverted somewhat by the fact that not just anyone can pull it - you have to have a certain special PSI power. It also helps that if a good-hearted person pulls the Needles, the Dragon wouldn't so much destroy the world as upgrade it.
In Vagrant Story, the city you fight in is the Cosmic Keystone. Yes, drawing on its power irrevocably damns your soul, and sometimes you can't even stop yourself from using it. Yes, it also unravels that pesky Laser-Guided Amnesia (OR DOES IT?). And yes, everyone and their grandmother has designs on the bloody place, including that Corrupt Church. All to the point where you don't know who might have the right idea up. Until the end, where it becomes a case of who's the last man standing.
Said Cosmic Keystone, named 'The Gran Grimoire', is the source of all magical energy in the world. And, in the Final Fantasy games that tie in with Vagrant Story, normally manifests as a book that created, and is holding together, the entire world.
The InfocomInteractive Fiction game Spellbreaker has its protagonist traveling the world in search of its Cosmic Keystones, which in a borderline subversion manifest as featureless white cubes that are utterly indistinguishable from one another (but can be written on to differentiate them; this was considered a neat feature when the game first came out). It turns out that this is all The Plan of the protagonist's evil magical doppelganger: you've been playing MacGuffin Delivery Service for him all along, and once you unwittingly bring all the cubes to him, he magically paralyzes you and uses the cubes to build a tesseract - a hypercube - at the center of which is the Cube of Magic. Once he enters the hypercube, reality will reconfigure itself around him - essentially turning him into a god - but the protagonist can use his Heroic Resolve to shake off the doppelganger's spell just in time to replace the Cube of Magic with something nonmagical, erasing your evil twin from existence... as well as magic, unfortunately.
Xenogears and Xenosaga both have the Zohar Modifier, an object that has existed since the beginning of the universe.
Chrono Trigger and Chrono Cross have a few of these — the Time Egg (the "Chrono Trigger"), the Frozen Flame and the Chrono Cross. In the Fan GameCrimson Echoes, the Frozen Flame is the prominent Cosmic Keystone, while the Time Eggs have become more easily manufactured and used (with both Balthasar and Lucca constructing them), suffering Keystone Decay by virtue of this.
The Seven Seals in Darksiders are essentially a countdown to Armageddon. Breaking the Seventh is the signal for everybody to engage in the massive cosmic winner-take-all power struggle that is the Endwar, with the Horsemen ready to clean up the mess when everything is resolved.
Demon's Souls has the Monumentals and the Archstones in the Nexus. The Monumentals, willingly transformed into half-living magical statues, sealed away the Old One the last time it went on a soul-devouring world tour, and created the six Archstones to bind together the remaining fragments of reality. If the Monumentals completely die out, or the Archstones get destroyed, cue The End of the World as We Know It.
NieR has The Shadowlord, the supposed Big Bad of the game. He's the reason that the Shades, AKA the unrelapsed souls of humanity haven't all gone insane and turned into monsters. Unfortunately, by killing him, Nier ends up dooming humanity to extinction.
Dark Souls has the Lord Souls, fragments of the First Flame. These flames created disparity in a once ordered and gray universe, and the Lords wielded the power of these Souls against the everlasting dragons. The dragons were defeated, and thus began the Age of Fire, the age of Lords. The premise of the game is that the First Flame is flickering, and the world is slowly dying as a result. The mission given to your character is to rekindle the First Flame to save the Age of Fire. But your true destiny according to Darkstalker Kaathe is to let the First Flame die so that the unique Lord Soul you inherited from your ancestor the Furtive Pygmy, the Dark Soul, can begin the Age of Dark, the age of humanity.
In Turok 2: Seeds of Evil, the destruction of the five Energy Totems will release Primagen from his prison and destroy our universe.
World of Warcraft had the Well of Eternity, a well created by the titans that poured magic out across Azeroth. When it was destroyed at the end of the War of the Ancients, it caused the sundering, which ripped the super-continent apart into the world as its known in the games.
In the Cataclysm expansion, a second is revealed; the World Pillar in Deepholm, responsible for keeping Deepholm (one of the parts of the elemental plane) from collapsing into the world.
In Legaia II: Duel Saga, the three sacred stones - the Pyrolith, Aerolith, and Aqualith - are tied to the Source Forge, the beacon of the world's creation.
Makai Kingdom has the Sacred Tome, which doubles as a valuable source of information as it knows everything about the Netherworld. Villain Protagonist Zetta sets it on fire out of spite after it said he'd end up destroying the Netherworld by being an idiot...which is precisely why it ends up being destroyed. He manages to preserve the tome by merging with it, however, leaving him as an angry-faced book for the entire story. This translates into the gameplay, as if he happens to get attacked by an enemy, all the manner of bizarre (And frequently harmful) things will happen.
Keyholes can also be used to outright alter a world. At the end of Kingdom Hearts: Birth by Sleep, Aqua uses the Keyhole at the Land of Departure to change it into Castle Oblivion.
Realms of the Haunting has the seven seals, whose breaking will plunge the world into eternal darkness, as envisioned by Florentine.
Justified, in Inherit the Earth: Quest for the Orb, as the titular Orb of Storms was created by sufficiently advanced humans. It has been used for generations to judge the growing and planting seasons and its holders have a huge advantage in managing their food supply. It's apparently the core operating system for some weather control satellites.
Gruntz has Warpstone Pieces. They're 4 pieces of a big circular rock with a spiral in the center, and getting them together is the only way the Gruntz can go back home.
battle-girl has the Great Machine, a massive computer at the center of the universe which acts as "source of cosmic order and enforcer of natural law."
The five Gates in The Order of the Stick are somewhat more reasonably founded than most examples: they were placed over flaws in space-time in order to keep the Snarl, the local Sealed Evil in a Cancanned. And the gods could indeed fix it, in the same way you can fix a horribly screwed-up computer by formatting and reinstalling... (which is to say, by starting over with a fresh world). The gods would do that if the Snarl is ever freed, so the protagonists are working to prevent it from being freed in the first place, for obvious reasons.
In Emergency Exit the main cast was assigned to collect "artifacts" in order to save someone's world from destruction, but it turns out to be a flat out lie and now nobody seems to know what they are for. It is shown that each artifact has a minor power, but implied that they do something far more spectacular when put together (hence an alternative collective name for them, "The Puzzle").
In City of Reality, the Aura Stones appear to be this for the various Alternate Universes. Each world has a master stone which allows its particular "reality" to exist, and removing or destroying this stone may have catastrophic consequences.
Cucumber Quest has the Disaster Stones, which, if all gathered, can be used to resurrect the Nightmare Knight.
Thundercats had scads of these. Most of the second season was taken up recovering the sacred treasures of Thundera in order to restore and stabilize said planet after it was originally destroyed.
Magi-Nation has the eleven Dream Stones. Actually, there's twelve; the Core has one, too. If they are brought together, they form the Core Glyph, which can seal Agram away for good. However, if Agram and the Shadow Magi get them, Agram can break free of the Core.
In the X-Men animated series, people with Psychic Powers proved to be Cosmic Keystones when brought together, as killing them all at once would have allowed Apocalypse to remake the universe in his image.
Albeit only if it was done in the Axis of Time, a kind of convergence of history existing outside of time. Plus, being in the Axis increases the psychics' powers, such that all of them gathered together collectively overpowered Apocalypse. So somewhat more stable than most Cosmic Keystones.
In Code Lyoko, entering "Code XANA" into a Way Tower will destroy the sector it is in. Furthermore, Lyoko can be deleted all at once by destroying the "Core of Lyoko" in Sector 5.
In Avatar: The Last Airbender, the spirits of the moon and ocean, bored with existence in the spirit world, came to live in the mortal world in the form of koi fish. If they are killed, the part of nature they represent (or the effect it has on other objects or something) will be gone forever.
Although one of them was smart enough to heal someone in exchange for them becoming a backup spirit.
In essence, the spirits took mortal form as a way of maintaining the balance of the cycles of the world. The destruction of one puts the other out of balance, in a manner which would destroy the world's cycles disastrously.
In The Legend of Korra, the Avatar Spirit is revealed to be not the spirit of the world, but rather a spirit of Light and Order named Raava. Raava dying in itself wouldn't have any horrible effects, light and order could still exist. It's just that while she spends 10,000 years regenerating, her Evil Counterpart Vaatu the spirit of Darkness and Chaos would have free reign to wreck havoc.
One episode of Futurama featured a box containing the universenote First it contained another universe which had its own box containing our universe, but they switched the two around at the end. Played for laughs, as even with warnings that it had to be treated as dearly as life itself, the box is shaken to listen for anything rattling inside (causing a small earthquake) and sat on (stretching out the picture horizontally).
The plot of Barbie & The Diamond Castle involves the heroines trying to keep the titular castle and the instruments in it out of the villain's hands, lest the world turn to "shadows and sorrow." The villain's actual goal in gaining the castle is to solidify her position as the only muse and rule all music, but those side effects will occur, apparently.
The Secret Saturdays: The eponymous pin in "The Atlas Pin", which was created by the Atlanteans to lock key tectonic plates in place. Tampering with it causes devastating worldwide earthquakes. Removing it will destroy the planet.