Adaptation Drift

An adaptation which starts off fairly close to the source material, but in sequels or later seasons, starts to become more of its own unique story.

Little details can add up — when the adaption decides to kill off one minor mauve-shirt instead of the other, it may seem not have much effect on that episode, but what happens when that minor character gets promoted to a main protagonist later in the source material? Do they bring the original Back from the Dead, or give the role to another character? Or should that storyline be dropped altogether, risking even more deviation down the line.

Can be a result of Real Life Writes the Plot, when actors quit, or budget constraints prevent the adaptation from going through with all of the expensive travel plotlines of the original. In other cases, drift will start to happen naturally, as the writers and actors start to get a feel for the story they're telling, which may not always line up with what the original creators had in mind.

If they do try to re-integrate plot points from later in the source material, the context may feel completely different.

This can be a problem if the adaptation in question is a prequel, which by definition needs to match a pre-planned ending. If the prequel has drifted far enough, trying to wrench it back into line with the original can result in Character Derailment and Later-Installment Weirdness.

This is a commonly done intentionally in Alternate Universe Fic, Alternate History, and other What If? stories with a single point of divergence from the original. After the point of divergence, further changes gradually accumulate, so the story moves through the next few Stations of the Canon before veering off into unknown territory.

Compare Overtook the Manga, when the adaptation has to start making up its own material because it's run out of source material to adapt; Gecko Ending and Adaptational Alternate Ending for cases when the ending is made up for the adaptation; Off the Rails; and Not His Sled.

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Examples:

Anime & Manga

• Black Butler (2008): Only the first 9 episodes are adapted from the manga. The rest of the first and second seasons opt to tell their own story.
• Fullmetal Alchemist has two anime adaptions: Fullmetal Alchemist: Brotherhood and Fullmetal Alchemist (2003). Brotherhood is a Truer to the Text that started when the manga was already almost finished. The other anime ran 2003 to 2004 and eventually Overtook the Manga, therefore its plot diverges around halfway through the series.
• Hyperdimension Neptunia the Animation adapts a few plot points from mk2 for the first half of episodes and Victory for the second half. And while it does change a few elements from those two games for the sake of the adaptation, as well as being an Alternate Continuity from the start, the anime mostly stays true to the games it's adapting from. But starting from the 13th episode, the anime began to distance themselves from the games by having an entirely original story. This would continued further with the three OVAs (Neptune's Summer Vacation, Nep-Nep Festival, and Little Purple Sunshine), as while it does take a few elements from VII (such as Adult Neptune saving the other Candidates from a monster attack and a brief cameo from Uzume at the end of the 4th OVA), the anime had already became its own thing, even including elements exclusive to the anime like the Purple Heart's Lilac COOL Processor in the 2nd OVA and Adult Neptune's Gen. Unit Processor in the 3rd OVA, the latter of which would later be reincorporated back into the games with Dimension Tripper Neptune: TOP NEP (which was based on the anime) and Neptunia Game Maker R:Evolution.
• Love Live! Nijigasaki High School Idol Club doesn't have much in common with its source material, Love Live School Idol Festival ALLSTARS, to begin with, but as far as Season 1 goes the anime at least adheres to some of the plot beats from the game despite drastically altering the context surrounding them. Come Season 2, however, and the plot completely diverges from the video game; Lanzhu and Mia are in it, and subunits are introduced, but aside from that everything in the anime's Season 2 is completely original.
• MegaMan NT Warrior (2002): The first two seasons were loose adaptations of the first two games in the Mega Man Battle Network series, but its next season, titled Axess, abandoned the game plotline in favor of dimensional crossovers between the real world and cyberworld and fusions between humans and their Navis.
• Neon Genesis Evangelion: The Rebuild of Evangelion film saga consists of four movies that start off retelling the events of the original 1995 TV show. The first film is a Compressed Adaptation of the first six episodes, making some changes that turn it into an actionized retelling. By the time of the second film however, things start diverging very quickly that it goes Off the Rails from the original and establishes an Alternate Continuity. The second movie in particular introduces a new character known as Mari Makinami Illustrious and has Shinji Ikari almost bring the end of the world, with the latter's consequences explored in the third and fourth films with completely new material not present in the source.
• The Promised Neverland was originally a manga with twenty volumes. When adapted as an anime, the first season was a faithful adaptation of the first arc. However, with the rest of the work being adapted into a single season, the anime took many creative liberties to condense the material.
• Rozen Maiden: The first season of Studio NOMAD's anime adaptation started off faithfully with following the original manga's plot. However, as a result of the manga being cut short because of Executive Meddling behind the scenes (until its 2008 Stealth Sequel came along to revive it), the second season called Rozen Maiden: Träumend deviated from the manga's initial plot by featuring a new plot centering around a new doll named Barasuishou, who claims to be the seventh Rozen Maiden doll until it's revealed at the end that she's just an imitation created by Enju, who aimed to surpass Rozen as the top doll maker.
• Rurouni Kenshin: While the 1996 anime series had some fillers early on, it remained faithful to the manga until the Kyoto arc. After that, the show diverges with its own original stories starting with the Shimabara arc and it ended with the Feng Shui arc.
• The Shaman King (2001) anime for the most part stays faithful to the manga right up until the defeat of Tao En, after which it almost entirely diverges from the manga with only certain tertiary events being adapted. These include completely changing Hao's entire character to make him more overtly evil and a Gecko Ending where Yoh actually defeats him as opposed to Hao winning the Shaman Tournament. This was due to dwindling sales and the manga being published at a slow rate.
• Teasing Master Takagi-san: Combined with Adaptational Expansion. While the anime does follow the manga's storyline, Seasons 2 and 3 began relying less on the manga and more on anime-original plotlines that highlighted the blossoming romance between the two main characters, Nishikata and Takagi. It's to the point that by the end of Season 3 and the 2022 Movie, the anime's story became its own thing in its entirety, distinct from the ongoing manga.
• Tsubasa -RESERVoir CHRoNiCLE-: Season 1 follows the manga storyline very closely but it's only in Season 2 that the show diverges from the manga starting with the Rekord arc where instead of following it up with the Acid Tokyo arc, it went with an anime original storyline. At that point, more anime original stories show up, and Season 2 ended with the characters saying And the Adventure Continues. The two OVAs released after the show adapted the Acid Tokyo and Nihon arcs ignoring the show's original storylines but they skipped the Celes arc.

Fanfics

• Dæmorphing started out as straightforward retellings of the Animorphs books where the only major difference was the existence of daemons. However, once Loren becomes a Team Member in the Adaptation, the changes start piling up, leading to the war ending in a completely different way.
• The Loud House: Revamped started as a standard self-insert The Loud House fanfiction before turning into a massive crossover with a huge cast ensemble and strict formula: Team Loud Phoenix Storm saves several girls who join Lincoln's harem.
• The Mountain and the Wolf: The Wolf's effect on the plot of Game of Thrones increases as time goes by:
  • The early chapters mostly feature the Wolf showing up and killing GOT characters shortly before they would have died in canon (Gregor Clegane, Ramsay Bolton, Petyr Baelish) and then leaving, so he has very little effect on the overall plot. Only after the Battle of Winterfell does he start having a broader effect on the world and other characters (his meddling causes Theon Greyjoy to survive the battle and join him as a Champion of Chaos, Beric is still alive, Varys is abducted before he can be killed, his pulling a Kill and Replace on Euron Greyjoy ensures the Golden Company's War Elephants are in Westeros).
  • While the next few chapters still follow the show's plot, it happens for different reasons: he abducts Jaime, Qyburn and Cersei so their bodies are never found, Daenerys accepts King's Landing surrender so he makes it look as though Cersei used magic to attack Daenerys and make her burn down the city, Daenerys is killed when she catches the Wolf trying to steal the Iron Throne.
  • After the Wolf interrupts an important moment in the show's finale (instead of a council banishing Jon Snow for the murder of Daenerys, Jon is now the Hand of the King), it goes into completely different territory: the Unsullied stay in Westeros to fight the Wolf; Missandei, Varys, Jaime, Qyburn and Cersei are his prisoners; Arya is nearly killed by Khornate cultists, and the mostly-united Seven Kingdoms lay siege to Harrenhal with help from the Unsullied, Dothraki and the Red Priests of R'hllor to drive back the forces of Chaos.

Film — Live-Action

• Harry Potter: The first two films were considered faithful adaptations of the books, but as the original source material got longer (over 500 pages per book) the films had to make more creative cuts, not helped by the fact that the creators didn't know exactly how the series would end until post-Harry Potter and the Order of the Phoenix (2007). This resulted in the filmmakers having to quickly correct for some characters, romantic pairings, and plot points Adapted Out earlier in the series that ended up having larger roles than expected in the later books, while making some bolder adaptation distillations and expansions to make it clear the films would be doing their own thing. Downplayed, since the endings were rather similar, they just took different routes to get there.
• Zig-Zagged by the James Bond films.
  • After five of the first six films were largely faithful adaptations of their respective novels (You Only Live Twice being the exception), the films became original stories that borrowed names, locations, and incidents from their namesake novels. The results range from In Name Only (The Spy Who Loved Me famously because Ian Fleming disliked the book, but its predecessor and successor are just as unrecognizable) to loose adaptations (e.g., For Your Eyes Only is its namesake story + "Risico" + an original MacGuffin plot, with a bit from Live and Let Die thrown in). By the Pierce Brosnan era, borrowing from Fleming stopped.
  • The Daniel Craig reboot films started with a Setting Update of Casino Royale with the reason for the villain's situation changed and presented as the first act rather than an Exposition Dump. Quantum of Solace borrowed one of the remaining unused Fleming names (but had nothing else to do with the namesake story) and included a finale inspired by one of the other Bond stories ("007 in New York"). Then Skyfall, Spectre and No Time to Die were completely original stories.
• 2023's The Three Musketeers: While both parts feature significant deviations from the source material, Part I mostly sticks to the general plot of the novel, while Part II tells an almost entirely original story with only some elements taken from the novel.

Live-Action TV

• 12 Monkeys started as an Adaptation Expansion of the movie 12 Monkeys. From the second season on, it moved far away from the original movie. Justified because not only was it adapting a single two-hour movie into an ongoing series, but also in that it started as a completely different, original project, and Executive Meddling turned it into an adaptation, so once the film's story was told, the writers were free to make what they originally wanted to.
• 13 Reasons Why: The first season is largely faithful to the book, albeit with a lot of Adaptation Expansion due to the difference in medium. From the second season onwards, it delves into completely original territory (although some plotlines build off what occurred in Season 1) and even adds new information or retcons to the more book-faithful elements (for example, Zach and Hannah are acquaintances in Season 1 and Zach has a crush on her, which is how they're presented in the book; Season 2 deviates from this to reveal they were exes.
• Being Human (US): The SyFy remake's first season was largely a close adaptation of the original UK series' first season, with similar story and character arcs and progressions of events — the US series premiere in particular had a near-identical synopsis and some shot-for-shot scene recreations from the UK series' premiere. Season 2, however, had almost nothing in common story-wise with the UK show's second season beyond picking up the first season's UK-paralleling plot threads, and Season 3 finally firmly established the US series as a narratively completely-separate show from the UK series.
• Clarice starts off as a sequel series to Silence of the Lambs before making sharp diversions from the source material — most notably its strong implications that Clarice and her friend/roommate Ardelia are more than friends, and revealing that Clarice's father was a Corrupt Cop.
• Fargo: The first season, originally intended as a miniseries, is a Stealth Sequel to the original film. The money buried by Showalter is a subplot, and many of the characters are Expies of the ones in the film (Lester Nygaard for Jerry Lundegaard, Molly Solverson for Marge Gunderson, etc). When more seasons were ordered the show adopted an anthology format telling of various interlocked crimes in the Midwest area, with the second season being about Molly's father, but kept moving further from the source material as more characters and events were added.
• Game of Thrones: The first couple of seasons were near-identical to the books, but incremental changes accumulated over time — by season 5, several characters were on a different storyline altogether, or just didn't exist (such as the Lady Stoneheart and Young Griff), before the series Overtook the Manga altogether and had to write its own ending just based off an outline by George R. R. Martin.
• The TV series Hannibal was originally presented as a prequel to the books, set prior to Hannibal being caught and put in prison. However, over the course of three seasons the story and character relationships developed to the point where it was outright incompatible with the canonical beginning of the books. Although the later seasons mix-and-matched storylines from the books, by the end of the show it was by explicitly set in an Alternate Continuity.
• House of Anubis: As the English version of the Dutch show Het Huis Anubis, the show took a few liberties with the source material even back in season 1, from small changes (the protagonist being a Foreign Exchange Student) to larger ones (like merging two villains into a Composite Character to streamline the plot). However, it wasn't until the second season where HOA began to create a unique plotline rather than continue to follow the plot of HHA, with the story ultimately going in a completely different direction.
• The Office (UK) was a vicious satire of Work Coms, using its mocumentary format to contrast the TV fiction of working in a quirky office for a wacky boss with the reality of how excruciating that would be in real life. Its adaptation, The Office (US), started off as a carbon copy of the original, but it drifted over time into a show about how much fun it is to work in a quirky office for a wacky boss.
• Scream: The TV Series: Inverted. The first two seasons follow the basic premise of the film series but largely do their own thing. The third season is a reboot that borrows more elements from the film series, even featuring the return of both Roger L. Jackson and the classic Scream mask, which were replaced by a new voice actor and mask.
• True Blood's first season followed Dead Until Dark, the first of The Sookie Stackhouse Mysteries, fairly closely. Each season after drifted further from the novels until the fifth season has only the barest bones of the novel. Season 2, already with dramatic differences from Living Dead in Dallas, had a Leaning on the Fourth Wall moment where author Charlaine Harris cameoed as a customer at Merlotte's:
  Charlaine Harris: I certainly never expected anything like that to happen here.
• The Netflix version of The Umbrella Academy was never extremely close to the comic books, as it incorporated several Actor Inspired Elements as well as Adaptational Diversity. However, the first season roughly follows the plot of the first book, while later on these changes snowball into an entirely different plot for many characters — for example, Victor's gender identity arc, and Allison's storyline being about racism when she was white in the comics.
• Westworld: While not a direct remake of the 1973 film, the series retained its setting (a historical theme park populated by android characters, focusing on the Wild West sector) and basic idea (androids begin malfunctioning and attacking the guests, although this time it's because they're becoming sentient instead of infected by a computer virus). That all changed in Season 3, which leaves Westworld behind to explore the real world beyond it, becoming more of a Cyberpunk narrative. The title becomes mainly The Artifact, as Westworld is never revisited until the very end of Season 4.
• Wire in the Blood: Being an Adaptation of the Tony Hill and Carol Jordan novels, the first episode is a mostly accurate adaptation of the first novel albeit updated to the present and slim lining a number of subplots (and a slightly different ending). The second episode however, whilst still roughly following the overall main plot, makes considerable changes from the second novel, with several major characters and subplots flat out removed (mostly due to the limitations of timing, being confined to one cast and setting). After that the episodes start being original stories, as at the time only one other novel had been published. Whilst the series did proceed to adapt two more novels (in season four and six respectively) following their publication, both again took significant deviations from the source material to fit with the established world they had created.
• You (2018): The first two seasons hue pretty closely to the plots of the first two books. But development on season three had already started when the third book was released, so the two bear very little resemblance to each other. As a result, seasons three and four have essentially no relationship to the third and fourth books, save some very loose thematic points.

Video Games

• Digital Devil Saga combines this with What Could Have Been. Originally, the plot of the game was written by Yu Gudai, but illness forced her to leave the project early, making Satomi Tadashi complete the story based on the notes she left behind. A few years after the release of the two games, she went on to put her original vision in the Quantum Devil Saga: Avatar Tuner series, while borrowing some elements from the videogames. The result is that the first game and the first two books follow more or less The Stations of the Canon, but show increasing levels of divergence in terms of plot, characters and their roles, and backstory, to the point that they're two completely different continuities with wildly different endings that are only similar in terms of themes.
• The Dune games made by Westwood Studios first inverted this from Dune II to its remake Dune 2000 by replacing the original Mentats with expies of Mentats from the David Lynch movie who made explicit reference to Duke Leto Atreides and Baron Vladimir Harkonnen, then played it straight with Emperor: Battle for Dune which replaced the higher-ups of each House with even more expies.

Web Animation

• Scootertrix the Abridged starts off as an Abridged Series of My Little Pony: Friendship Is Magic, with the first three episodes sticking closely to the plot from each corresponding episode of the original show. But subsequent episodes introduce completely different plots from the original show, villains from later seasons show up in the middle of season one, and the series develops an overarching plot about Equestria going to war. The series creators started frankensteining footage from different episodes (and even commissioned completely original animations) to tell the story they wanted—to the extent that Scootertrix's original final episode doesn't include any footage or plot details from the corresponding Friendship Is Magic episode. The followup series, Scootertrix the Epilogue, uses completely original animation and doesn't even pretend to be an abridged series anymore.

Webcomics

• The Monster Under the Bed: The first chapter of the Comic-Book Adaptation has more-or-less the same plot as the first chapter of the Web Serial Novel, albeit with some minor changes (such as Tim's two attempts to make a mousetrap in the book being combined into one attempt in the webcomic), but the later chapters go in an entirely different direction only a few plot elements borrowed from the novel. Whereas the novel did a Time Skip to Tim and Shadow's late teens, the comic stays in their childhood years, with numerous characters getting reworked to fit this new setting (the novel's Big Bad Lord Terminus is reduced to a supporting character while his dragon Nightmare is turned into an Alpha Bitch). Chapter 4 subverts this. The Time Skip finally happens and Terminus usurps is superior to take his throne, setting himself up to be the Big Bad again.

Web Video

• The Auralnauts' Star Wars Reimagined is a Gag Dub that edits the original Star Wars trilogy to make them more consistent with the prequel trilogy, sequel trilogy, and the various spinoff series. The first episode follows the original plot of A New Hope, just with a lot more exposition from Darth Vader. Things start to change in their version of The Empire Strikes Back, where Lando deliberately turns Han over to the Empire as revenge for the death of L3, and Darth Vader invites Luke to Take a Third Option with him rather than tempting him to the Dark Side. Their version of Return of the Jedi continues this plot thread, with Luke and Darth Vader united against Emperor Palpatine from the beginning. And they kill the Emperor with the power of "the dyad", implying he's now Deader than Dead in a way that prevents the sequel trilogy from ever happening.

Western Animation

• Teenage Mutant Ninja Turtles (2003) started off as a much Truer to the Text Animated Adaptation of the original Mirage comics than the last cartoon, but started piling up its own original elements like new characters and Shredder being an Utrom and making more and more original stories instead of just adapting comic story arcs until it became a very different incarnation of the franchise by seasons 3 and 4.
• For the first two seasons, the creators of Thomas & Friends were contractually obliged to only make episodes based on existing The Railway Series stories and other material written by the Awdrys. Season 3, however, had many original episodes, and they stopped adapting the books entirely in season 5 after Wilbert Awdry died.

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