Trip: Every day.
T'Pol: Good. Then you've already come to the conclusion that, without humanity, there's no one to combat these Sphere-Builders. Their Expanse will continue to grow, encompassing one system after another, including Vulcan. Your world is no longer the only one in jeopardy.
Maybe you're Trapped in Another World, fighting monsters and saving people so you can find your way home... and then you do. Or maybe you've gone to another world after adventuring around your home, and found something a little too familiar about this place. Maybe you even go between worlds on a regular basis, and things are getting serious on the other side.
Either way, you discover the two worlds you've been flitting about in have a strange connection. It doesn't matter what it is, but it let you into the other world, and it can let something else out into yours. Generally it's monsters roaming the streets, but there can be other effects. Perhaps the Big Bad is an Evil Overlord who has encountered your homeworld and has decided to forcefully add it to their domain. Perhaps the two worlds are threatening to collapse on each other. If the more mystical of the worlds is based in a computer realm, expect a deadly effect on your hometown hospitals and roads.
The other world's still in danger, but now so is yours, and the Muggles certainly can't do anything about it. What do you do? You grab your adventuring party and a couple of friends from your homeworld, and you go out to save them both.
Contrast with Up the Real Rabbit Hole or Expendable Alternate Universe, where both worlds are in jeopardy but the heroes don't see the one that isn't their own as real enough to merit saving. May overlap with The Call Knows Where You Live.
- The various series of Digimon often culminate in a threat that could destroy both the Human and Digital Worlds:
- Digimon Adventure: Apocalymon spitefully attempts to self-destruct and create an explosion powerful enough to annihilate both worlds.
- Digimon Tamers would've just been "save Earth", but the Big Bad was directly tied into both worlds, and could only be defeated from Earth with help from both sides.
- Digimon Frontier had Lucemon attempting to go rampage on Earth after devastating most of the Digital World, but the heroes drag him back before he can actually make it there.
- Digimon Data Squad had the two worlds set to quite literally collide with each other. The Final Boss King Drasil initially wanted to let this happen in a way that would destroy the Human World but leave the Digital World mostly intact; however, after enough setbacks and his minions turning on him, Drasil instead tries to force a mutual annihilation.
- It turns out that Those Who Hunt Elves need to get back to their home dimension to prevent it from fatally merging with the one they've found themselves stuck in. So their quest to get sent back becomes all the more important.
- In MÄR, Ginta's world and MÄR Heaven are connected largely by Snow's existence as a clone created from a fragment of Koyuki's soul. The Orb is also the manifestation of all the evil in Ginta's world as well. His plan was to use the connection between Snow and Koyuki to rip open a giant portal between the worlds to conquer Earth as well. In the end, Ginta ends up saving both worlds and Snow and Koyuki merge into a single person. Note this is only in the anime, in the manga the connection is different and the Orb's plan... doesn't make a whole lot of sense.
- Planet Ladder features a girl who discovers that there are nine dimensional Earths engaged in war and are moving towards collision with each other. She is prophesied to be the "Girl of Anansi" who can save only one of these worlds, but journeys among all the worlds to search for a way to save them all.
- Towards the end of the second series of Sonic X, the two worlds are revealed to be merging into each other again, with the catastrophic effect of canceling out each others timelines and causing time to come to a stand still. The only solution is to send the Sonic characters home.
- Watashi No Messiah Sama starts off with Trapped in Another World, with occasional visits back home. Then monsters appear on Earth, and eventually Earth is threatened with destruction. Naturally, our heroes can't save just one of the worlds.
- In Tamagotchi: Happiest Story in the Universe!, Kikitchi staying in one of the Flying Library's Portal Books has an effect on Tamagotchi Planet due to a page in the book being missing, causing the story within to loop endlessly. As a result, Tamagotchi Planet is at risk of being turned into paper on top of the book becoming unstable, and Mametchi and co. have to save both of these worlds.
- Almost subverted in the third issue of the JLA/Avengers crossover miniseries, both groups of heroes are unsure they want to restore their universes when they witness the Face Heel Turns, Heroic Sacrifices, Suspiciously Similar Substitutes, and With Great Power Comes Great Insanity that they will experience in the "correct" universe. Out of everyone Green Lantern Hal Jordan, who has the most to lose, argues they don't have the right to play God with the two universes, causing the heroes agree to restore reality.
- Zig-Zagged in Doomsday Clock. After the narcissistic Knight Templar Ozymandias' Utopia Justifies the Means plot failed in his own universe and he ends up in the DC Rebirth universe, he comes up with a plan to "save" both worlds by deliberately engineering yet another Darkest Hour for the DC heroes as part of a Batman Gambit to get Superman and Dr. Manhattan to fix everything. It works, but whether it was because of or in spite of him is hard to say.
- In Wonder Woman storyline "Judgment in Infinity", a group of heroines come together to save five parallel Earths from the Adjudicator.
- Initially, the end goal of the heroes of Infinity Wars was to undo Gamora's merging of half the universe, but things take a turn in the fifth issue of the main story, in which Adam Warlock informs the Soldier Supreme about the heroes' intentions, and the Soldier Supreme protests in response, refusing to give up his life for the sake of bringing back Dr. Strange and Captain America as two distinct beings again. The goal from that point forward, then, is to restore the regular Marvel Universe while preserving the Warped Universe within the Soul Stone.
- The Captain of the Virtual Console has this as its plot. Gancena must save the video game worlds and her own.
- In We Are All Pokémon Trainers, when given the choice, the J-Team decides to have Dialga and Palkia fork the AU inadvertently created by Cyrus into its own separate universe, despite the fact that it replaced their original universe, because they deemed it to have just as valid an existence.
- Taken to the extreme in Infinity Crisis, as a comparatively small group of heroes plan to save the entire Multiverse.
- In Barbie and the Secret Door, the heroines must save the magic of all realms of Zinnia.
- In the fourth Pleasant Goat and Big Big Wolf film, Mission Incredible: Adventures on the Dragon's Trail, the goats learn that dragons are responsible for making the clouds, stabilizing the soil, and holding the trees up from underground in the Green Green Grassland and that the destruction in the Dragon World is making them panic, affecting the Grassland. Thus, they have to save the Dragon World if they want to save the Grassland.
- In My Little Pony: Equestria Girls, Twilight Sparkle goes to a High School AU featuring human counterparts to her friends and most of the show's cast. While her main objective is to retrieve her crown where her Element resides from Big Bad Sunset Shimmer, she also quickly makes a friendship with her counterparts. This becomes a plot point when at the film's climax, Sunset threatens to destroy the portal connecting the two worlds if she didn't give her the crown. Twilight reasons she'd stay to help them, even if they'd both be doomed to never return to Equestria, since Sunset would be free to hurt her friends either way. Her bond with her new friends is strong enough to summon the Elements of Harmony and defeat her One-Winged Angel form. Only when she ensures that her friends would try to show Sunset Shimmer kindness after stripping her of power, does she cross back to Equestria. Nor does she forget this world after leaving, coming back in the next movie to help her human friends and a reformed Sunset Shimmer confront the next magical threat. Sunset, despite being from Equestria like Twilight, never shows any inclination to return after her Heel–Face Turn and makes the human world her home, defending it from magical threats. The series then continues on for more entries that don't involve the main series characters at all.
- The second half of Last Action Hero has Danny returning to the real world and bringing fictional action movie hero Jack Slater with him. Unfortunately, Benedict is there as well, and he's got the ticket to travel between movies and the real world to bring through anything he wants.
- Sort of done in MirrorMask. By saving the dreamworld, Helena also saves, symbolically, at the very least, her mother's life, and stops "her world" from being shattered. It's not as Narmy as it sounds.
- Technically, the titular heroine from May Bird series has to save "only" the Ever After world, but since all humans (including herself) will inevitably go there after death, this affect everybody on Earth as well. And the Big Bad is actively interfering with Earth, too, and it's only a question of time when he wrecks the Earth directly.
- The Magician's Nephew, when Diggory lets Jadis loose in London and then in Narnia.
- The Apprentice Adept series; Stile is a native of science-based Proton, but is brought to magical Phaze as part of a Gambit Roulette to correct an imbalance that would destroy both worlds.
- In Aaron Allston's Doc Sidhe, the protagonist is transported from the "grim world" (ours) to the "fair world" (Faerie), where he discovers a plot to subvert the connection between the worlds, threatening both. Both worlds are again threatened in the sequel, Sidhe-Devil.
- In the Everworld books, it would be a bad thing if the gods crossed over into the world of our own, or if aggressive human men with guns crossed over into the world of Everworld. Both of these dangers threaten to happen over the course of the stories.
- In Keys to the Kingdom, Arthur has to deal with threats in both the House and on Earth, particularly since if the House falls, so does the rest of the Universe.
- Mark Anthony's The Last Rune series, which features characters spending time in, and crossing between, Earth and the otherworld of Eldh. These include multiple villains and world-threatening dangers.
- Coraline, where the titular heroine must beat the Other Mother to save her parents and stop Other Mother from kidnapping children.
- Stephen King's The Talisman sees Jack flipping between our world and the 'The Territories' in an attempt to save his Mother from dying, this also has the side affect of saving the Queen in The Territories as they share a magical link.
- The Dark Tower, although in this there are many worlds and Roland and his companions must save all of them (since they will all be destroyed if the Dark Tower falls). However, Roland's world and Earth are the main ones that the heroes focus on.
- Much of So You Want To Be A Wizard by Diane Duane is spent in an alternate universe where the Lone Power has already put out the sun. At the climax, the protagonists make it back into their own universe, but the Lone Power follows them through the worldgate and they have to stop it...
- The Affably Evil villain in Everlost is trying to kill everyone and destroy everything in the real world so it will all be "preserved" in Everlost.
- In Deep Secret, the protagonists from Earth get involved in a succession crisis in the Koryfonic Empire, which spans several alternate universes. If the villains are successful, there will be bad consequences for universes beyond the Empire, including Earth's.
- The third season of Star Trek: Enterprise somewhat inverts this. Since Starfleet is fairly new to the galactic stage, their conflict with the aggressor Xindi is largely ignored by the galaxy at large, including their Vulcan "allies". As the story unfolds, however, it becomes clear that the Xindi are just Unwitting Pawns of the Sphere-Builders, Abusive Precursors who plan to invade and transform the galaxy into something more hospitable to their kind, which will doom all sapient life — human, Xindi, Vulcan, and other — to extinction. This revelation causes a schism within the Xindi, most of whom flock to humanity's side against their former-deities, and the Andorians also show up to help at the end.
- In MythQuest, there is a god named Gorgos who lives to change and destroy mythology. He escapes into an advanced computer system where he has the power to alter the outcome of the myths. Minor changes only seem to cause a ripple effect in global knowledge of the myth, but when he tricked a character into almost causing Ragnarok, a large earthquake was felt in the real world.
- The Famous Jett Jackson: Referenced in The Movie:
Silverstone: If Kragg gets this world, it's only a matter of time until he comes for yours.
- The cornerstone of Fringe and its mythology is an Alternate Universe, and the protagonists of the show (from the prime universe) are using Mad Science in an attempt to save both worlds after the first attempt at crossing from one universe to another resulted in a parade of soft spots, cracks in the walls of reality, breakdowns of the laws of physics, swirly energy thingies, negative earth wedgies, dogs and cats living together, etc. that threaten to destroy both universes. This is juxtaposed by the characters from the Alternate Universe, who believe the only way to save their universe is to destroy the prime one first (and they may be right). Or not, as it is revealed that the two worlds are permanently intertwined; therefore, the only way for any character to save their world is to save both of them.
- Mirai Sentai Timeranger has what could be called a "Save Both Times" variant towards the end. Captain Ryuuya reveals that there were two possible timelines leading to his current time, with a cataclysm happening either in the 21st or 31st century, but both of them had something in common: he himself would die as TimeFire. His plan in sending the Timerangers to the past was to ensure that the cataclysm would happen in the 21st century and have someone else die in his stead, and then wipe their memories to cover his tracks. The Timerangers however chose to go back and save the past as well, with the implication that in doing so they also saved the future.
- Arcana Heart: An angel with a God complex is trying to break down the barrier between the real world and the Elemental world. She almost succeeds.
- In Digimon Survive, the cast is trapped in the Digital World and spend most of the game desperately seeking a way back. They later learn that the Big Bad is an Eldritch Abomination seeking to take over the Digital World and destroy the human world, forcing them to deal with it first before they can return.
- Sonic The Hedgehog:
- In Sonic Rush Blaze is trapped on Sonic's world with the Sol Emeralds. If the Sol Emeralds aren't returned, both worlds will be destroyed.
- In Sonic Rush Adventure, Sonic and Tails discover they are trapped in Blaze's world. Eggman and Eggman NEGA team up at the end of the game to steal the Jeweled Scepter, which keeps the two worlds separated.
- Outcast: Opening the portal between the two worlds creates a black hole which will swallow up the Earth... unless you enter the alternate universe to figure out how to stop it. It turns out the alternate universe needs to be saved as well.
- Another Century's Episode 3 features a "save both worlds" plot, as some Applied Phlebotinum that exists in both worlds creates a dimensional rift, pulling the two Earths together due to gravitational forces. Also connects to Eureka 7 pretty significantly, since it's an Intercontinuity Crossover.
- Tales of Symphonia soon becomes this type. The Big Bad's Evil Plan alternates which world is in trouble but both ultimately have to be saved for either to have lasting peace.
- In Mortal Kombat vs. DC Universe, the simultaneous defeat of Shao Khan and Darkseid has caused the worlds of Mortal Kombat and the DC comics to begin to merge, with potentially dire results if not undone. The kombat fought between the denizens of both universes also serves to accelerate the process. It's not until Superman and Raiden overcome their differences that they can overcome Dark Khan's influence and save their worlds.
- The Legend of Zelda: A Link Between Worlds: Link starts out trying to save Hyrule, but soon finds that its counterpart, Lorule, is in even worse shape. In the end, it looks as though Hyrule will be saved at the expense of Lorule, which would make this a subversion... but Link and Zelda then wish on the Triforce for Lorule's Triforce to be restored, saving Lorule, and making this Double Subverted.
- The Twin Worlds of Stark (i.e. our familiar Earth) and the magical Arcadia in The Longest Journey have been one and the same twelve thousand years ago, and the biggest danger they face is an uncontrolled collapse back into each other. In this regard, April isn't saving Arcadia only to learn that she also has to save Stark—much rather, she is saving Stark, only to learn that in doing so, she also saves Arcadia.
- Similarly, Amy from ZanZarah: The Hidden Portal saves the world of Zanzarah from the dark forces, but in doing so, also restores magic to her own mundane world, which had lost it long ago.
- In Rakenzarn Frontier Story, the Realmwalkers take every universe as equally important. And as they play the role of Guardian of the Multiverse, it is literally their job to make sure all of them stay safe.note
- The Shadowbringers expansion has two worlds that must be saved in Final Fantasy XIV. The Source is the game's main world and the First is a parallel world of the Source. In order to prevent an eighth calamity occuring on the Source, the player character is whisked away to the First to prevent the Flood of Light from destroying that world. Should the First be destroyed, its effects would transfer to the Source since the two worlds are linked. The is made apparent by the Crystal Exarch who comes from a Bad Future where the calamity on the Source happened and plunged the world into chaos and lawlessness.
- In Undertale, if the player chooses and persists at the "Genocide" path, as the human cuts through monster after monster, it becomes clear to the survivors over time that they're not going to stop at the monsters' world, but they plan to keep going upon returning to the surface, which only adds to why they're all trying to stop you. At a certain point in the final minutes of the game, still underground, the fallen child leaves the player's control, has plans that become obvious, and in case you thought different, a short, haunting conversation against says the matter is no longer debatable. (In the main version of the story, playing the "Neutral" story or pacifistic, there's a dilemma that emerges — the monsters of the Underground are trapped there, but the terms of their breaking free means the vengeful king will make war on the human world, and the projected outcome goes, destroy it.)
- The plot of YU-NO eventually comes down to this. Takuya is whisked to a different dimension, Dela Grante, which is increasingly plagued by earthquakes attributed to an impending apocalypse. Takuya learns from those in the know that 8000 years ago, Precursors constructed Dela Grante to cycle his dimension in an interdimensional orbit, but a calculation error made the trajectory gradually shift and ultimately hit Earth. A full collision is narrowly avoided, but at the cost of Dela Grante not surviving and its remains crashing into Earth 8000 years earlier.
- In Ni No Kuni: Cross Worlds, after progressing far enough into the story, you learn that Levant's corruption is powerful enough that if not put in check it will eventually seep into the Earth as well. Thus by continuing to fight you are saving not only the world of Ni no Kuni, but also the Earth that you came from.
- In Amphibia, this became the goal of the final season. After learning that Andrias and the Core intended to invade all worlds out there, including Anne's, the heroes were driven to not only stop the invasion of Earth, but to liberate Amphibia.
- In Batman: The Brave and the Bold, when a Depopulation Bomb threatens to kill all life on Earth, Batman and Red Hood teleport it to another dimension. It turns out (as in, we find out they already knew) everyone on that Earth were already zombies, so the bomb's explosion was completely harmless. Additionally, this episode primarily takes place in an Evil Counterpart world, similar to Earth-3 of the comics. Batman doesn't just want to escape this world, he wants to make it better (since, in this world, The Bad Guy Wins is a regular occurrence). He frees the captured heroes, who are now being led by Red Hood, and the villains have been defeated. Batman only leaves when he feels like the native heroes have a good handle on things.
- The Codename: Kids Next Door episode "Operation: P.O.O.L.", where the heroes don't try to just escape the horrible Mirror Universe. They manage to actually make it better.
- In Megas XLR, Coop ends up in an alternate reality where he destroyed the Glorft, turned evil, conquered the world, and worse, lost his gut and became ripped. The real Coop decides to take care of his evil self, only to get Megas destroyed. Instead of simply pressing the Reset Button, he steals the alternate Coop's abandoned Megas, leads the Glorft against Evil Coop's forces in a final epic battle, and gets Evil Coop trapped between the universes. It's as awesome as it sounds.
- One episode of The Super Mario Bros. Super Show! brings Mario and Luigi back to Brooklyn, but also Bowser and company as well. They have to save Brooklyn and the Mushroom Kingdom from Bowser.
- An episode of the Dungeons & Dragons (1983) cartoon had the kids finally get back to their own world, but Venger followed. When they realize their weapons won't work on Earth, and it's made clear by Venger he'll lay waste to Earth as he did to the Realm, the kids must go back to prevent Venger from following through.
- Averting Expendable Alternate Universe seems to be the logic Samurai Jack lives by in his Bad Future. He repeatedly turns down the chance to return to the past and kill Aku before he could ever take over the world and gives it up to help his new friends. While this may seem Lawful Stupid in that he'd negate the Bad Future so he'd never need to save his friends, it may be that he's just too kind to take risks. Thus the best option would be to destroy Aku in the future and then return to the past and destroy him there. Ultimately, Jack kills Aku in the past, which does indeed erase the future he was sent into—include Ashi, his lover who he met while he was there. Although heartbroken, Jack concludes that restoring the Earth was worth the cost. Jack's allies were implied to have felt the same, as being told of Jack's goal to erase "the future that is Aku" did not keep them from coming to his aid.
- Turtles Forever: The 1986 and 2003 TMNT versions team up to stop 2003 Shredder and save not just their own worlds, but the entire TMNT multiverse.
- Downplayed in season 1, because Meridian was isolated from the other worlds by the Veil specifically to contain Phobos. However, Earth would still be endangered due to portals opening between the two worlds, enabling Phobos's forces to manifest on the heroes' hometown.
- The second season ramps up the Sliding Scale of Muggle Involvement, leaving the Guardians increasingly playing defense even on their own turf. In part because the Veil is now down, and also because Nerissa's goals include stealing Will's Heart and taking over the whole universe. Come the finale and the newly empowered villain Cedric outright decides to attack their hometown on Earth, in full view of everyone.