An installment in a series begins with a radical change to the status quo that the characters don't seem to notice or comment on.
Say you're watching your favorite TV show. All of a sudden, and usually at the beginning of an episode, something happens - a character who died is now alive, or the setting is completely different. Something is obviously up here, and you can't wait to see how the characters react. But then, they don't. It's not that they don't notice this change, but it's treated as if it's completely normal.
This could be anything from a Dream Sequence to an Alternate Universe. The point is, the audience doesn't know what's going on because the characters are, at first at least, treating this interlude as a completely normal occurence. Like In Medias Res, the audience only finds out what is happening later on. Compare Elephant in the Living Room, when characters aren't talking about it but do notice, and contrast Ripple-Effect-Proof Memory. When a timeline has been changed, everyone who doesn't have a Ripple-Effect-Proof Memory is covered by this trope. Examples of that trope don't have to be added here. See also Backstory Invader, a character who can cause this.
- The "Endless Eight" arc in the Haruhi Suzumiya anime is presented like this during the beginning of the "Groundhog Day" Loop.
- One Piece: The Hobby-Hobby Fruit can turn living beings into 'living' toys. Anyone who's a victim will be completely forgotten by everyone who ever knew them, including family and friends. They're also trapped in their new bodies since the fruit's user can force them into a contract of complete obedience but still allows them to think and feel. Once the user is defeated, the transformations and amnesia is entirely undone.
- Ushio and Tora: Towards the end of the series, the Hakumen causes Ushio's existence to be entirely forgotten. Every human character meets him for the first time, and are quite angry at the familiarity he displays with them. Even one of Ushio's father's allies doesn't recognize him, saying he never had a son. Fortunately, it turns out Tora still remembers him, and together they end the curse.
- Wanted: At some point every supervillain banded together to rewrite reality so that not only did the world forget superheroes were real, the superheroes forgot as well (the supervillains, for their part, operate in secrecy). One villain killed his nemeses (Batman and Robin expies) by dunking them in a vat of acid, they kept screaming that they weren't superheroes, they'd just played them on TV.
- Emperor Joker: The comic starts with Superman as a dangerous criminal locked up in Arkham Asylum and trying to escape Bizarro's clutches every day, Lois Lane as a bald Corrupt Corporate Executive, the Justice League as a bunch of supervillains and the actual DC supervillains as a rag-tag bunch of heroes, all treated as if this is the natural state of things. It's only revealed halfway through that all of reality has been perverted by The Joker after he acquired the powers of Mr. Mxyzptlk, which only those two characters are initially aware of.
- Wonder Woman: Odyssey technically takes place in the same continuity as Wonder Woman (1987) and Wonder Woman (2006) but the Amazons timeline has been altered by Clotho so that Themyscira was destroyed when Diana was very young and the few surviving Amazons are now living as hidden refugees. Neither Diana, nor the surrounding Amazons, have any memory of NOT being driven from the destroyed Themyscira or living in the following exile, though Diana running into a character who does remember the previous timeline helps her restore it...just in time for Flashpoint to destroy that version of the universe and replace Diana with a Darker and Edgier version for Wonder Woman (2011).
- One Sci-Fi anthology comic had a trio of scientists experiment with a time machine by examining specific moments in history. Each time they send their probe back, it inadvertently destroys something or someone and alters their present unawares. This regresses their culture to the points in history they tampered with, until they altered the entire human race by preventing life from leaving the ocean. Even then, as aquatic creatures, they get the bright idea to meddle with the creation of life on Earth, which is where the comic ends once they initiate the experiment.
- In Jonathan Joestar, The First JoJo, After defeating Heaven Ascension Dio, everyone is sent back to their original time. Nobody (except for Jotaro) remembers the journey at all, but looking at all the photos taken over the course of the adventure jogs their memories.
- In Robert Sheckley's Mindswap, the ending is the protagonist getting his body back in a parallel dimension, and then doubting whether he's back in his own universe, or still in a parallel one. He checks carefully, but... no. Same three red suns, same egglaying mother.
- Ursula K. Le Guin's The Lathe of Heaven. When Reality Warper George Orr has an "effective dream" and changes the world, no one remembers what the original world was like except him and anyone who was present when he had the dream.
- Animorphs: Megamorphs #3's first chapter ends with the Wham Line about people owning slaves, with nobody seeing a problem. It gets worse from there, with Rachel nowhere to be seen, Jake being a egomaniac asshole considering selling out Cassie to the government for disapproving of American imperialism, and writing off entire chunks of humanity called Primitives. When the Drode restores their memory to the real timeline, they retain the branch timeline's memories and feel sick to their stomachs. For the rest of the book they have Ripple-Effect-Proof Memory, but retain the memory of what will happen if they fail.
- Isaac Asimov's "Gimmicks Three": After Welby goes back in time, his contract disappears, and Shapur, the demon, doesn't understand why. To get an explanation, they restore his memory of the original timeline and Welby happily brags about the escape clause he discovered in the contract.
- William Tenn's "Brooklyn Project" ends with an official demonstrating that the time travel experiment had changed absolutely nothing... except that the reader is fairly certain that neither him not the audience were Blob Monsters when the demonstration started.
- Also by Asimov "Left to Right" is a Real-Person Fic starring his friend Robert L. Forward. He's created a device that will convert anything into "mirror matter", but when he tests it on himself, he's disappointed to find that his heart's still on the same side, as is his appendectomy scar. He's as sure that nothing's changed as he is that his name is Robert L. Backward.
- In "The Only One" by David S. Garnett, the protagonist uses time travel to go back to when he first met his wife, only to find that random fluctuations mean events don't quite happen the same way, and he doesn't meet her at all, so he goes back again, several times. While he's aware of this difference, he doesn't realise that every time he travels back, society and technology somehow move forwards (he started out in the Victorian era, and it advances to a Cyberpunk future) remembering this as being the way it happened. The story ends with him checking his recording (which was originally a phonograph strapped to his back and is now an internal memory chip) to make sure he's not forgetting anything, and getting a cyberpunk version of the story's opening lines.
- Buffy the Vampire Slayer:
- In the episode "Superstar" even the credits are changed to show the change of a spell that makes Jonathan into a Black Hole Sue.
- The first episode of season 5 introduces Dawn, Buffy's younger sister who didn't exist before this episode. Everyone (including Buffy) remembers Buffy as always having a younger sister.
- Hikonin Sentai Akibaranger: The second season begins with a recap of the first season that gets progressively less consistent with what actually happened but none of the characters are aware that anything changed except for Malshina, who doesn't reveal that she remembers the previous season until much later. Additionally, the activities of the show's new Big Bad are causing other changes to reality which the main characters do notice and have to figure out how to reverse. The new character Luna initially does not have the Ripple-Effect-Proof Memory that the others have and so her memories change whenever the heroes undo the villain's changes.
- Stargate SG-1: "The Fifth Man" starts with the team in a crisis situation, with only 3 of the team's members able to escape, and the other two trapped on the other side of the gate. Except that the team only has four members.
- Star Trek: The Next Generation:
- The episode "Yesterday's Enterprise" opens with the Enterprise-D coming upon a time rip with the Enterprise-C (lost decades earlier) emerging. Suddenly, reality is changed and the Federation is now involved in a war with the Klingons. On top of that, Tasha Yar (killed in season one) is still on the bridge crew (in place of Worf, logically — no Klingon would be on a Starfleet ship). No one notices anything is different, although Guinan suspects something is wrong.
- The episode "Conundrum" has an unknown alien ship cause a bit of Laser-Guided Amnesia on the crew and alter the computer records of the ship to make the crew think they are at war with another alien race called the Lysians, who are enemies of the race that screwed with their minds. For good measure, they also have a member of their race infiltrate the crew and pretend to be the Number Two — no one recognizes him, but of course they don't recognize each other either. Everyone is initially caught in the ripple, but Picard eventually does some Spotting the Thread.
- "My Heart Will Go On" features a fallen angel going back in time and changing the timeline, preventing the Titanic from sinking, and causing all sorts of ripple effects. Sam and Dean are blissfully unaware that they're living in an altered timeline until they discover it over the course of the episode because of the actions of another supernatural being who is trying to undo the changes made by the angel.
- Another episode has Sam & Dean Winchester leading completely different lives as unrelated people Dean Smith and Sam Wesson, an executive and an IT guy working at the same firm who get sucked into a supernatural mystery. Turns out it's a Secret Test of Character by some angels to prepare them for the intensifying war between Heaven and Hell.
- The episode "Nihilism" opens with Dean owning a bar alongside Pamela Barnes, despite her being dead for a decade at that point (and for that matter, she can see, despite having been blinded some time before her death). When a quick sequence of events involving the two of them play out repeatedly, it quickly becomes apparent that Dean is stuck in a Lotus-Eater Machine, placed there by Michael after being possessed by him at the end of the previous episode.
- In Torchwood, the episode "Adam" starts off with a new (to the viewers) team member Adam in the opening credits who's supposedly been with the team for the last three years. Turns out he's an alien who's infiltrated them by inserting years of fake memories into the Torchwood teams' minds.
- WandaVision: The entire premise of the series is that Wanda Maximoff and the Vision are living out a domestic sitcom life in the town of Westview, New Jersey and getting into all sorts of wacky hijinx to hide their superpowered nature from their neighbours. Right from the start the audience is aware that something is very, very wrong with this picture despite none of the characters treating this situation as odd in any way. Aside from the confusing Genre Shift from the rest of the MCU, Vision is Back from the Dead without explanation. It's gradually revealed that Wanda is mind controlling an entire town into playing along with the life she wished she and Vision could have had. When people from outside the town who haven't been Caught in the Ripple try to interfere, things go from bad to worse.
- One episode of the Weird Science sitcom (based on the movie) starts with Gary and Wyatt getting bullied which they're used to, but they seemingly have no knowledge of Lisa. They then discover evidence of her existence and look into her. It's later discovered they told a classmate about Lisa and the classmate made Lisa her slave. One of the first things she did was wish Gary and Wyatt forgot about Lisa.
- BlazBlue: Central Fiction: From the beginning, the game somehow seems to revert the timeline and events to that of the first game, i.e. 2199. Most people act like they would during that part of history. There are a few people, however, who notice something's wrong. It's revealed later that the world they're in isn't the same world they (or the audience) know, but rather a Pocket Dimension called "Embryo", and most people's memories are reverted to the events of the first game. They do, at least, regain their memories around the end of the second act.
- In Dishonored 2, if you somehow manage to restore Aramis Stilton's sanity by manipulating the past, he will join you on the Dreadful Wale in the next mission, acting like he's been your ally all along — which he has, in this new timeline. What's more, Meagan Foster also suddenly has a right arm, which she had lost in your original timeline while trying to discover what happened to Stilton. Nobody except the protagonist (Emily or Corvo) notices the changes, however, since only the protagonist (and the Outsider) have Ripple-Proof Memory.