Throughout Assassination Classroom, Koro-sensei undergoes a subtle, important shift in personality. Formerly the exceedingly skilled human assassin known as the "God of Death", he slowly acclimates more to the responsibilities of a teacher and to empathy itself, only recently instilled in him by Aguri Yukimura, a gentle young teacher assigned to observe him during his confinement. This is justified, because the "tentacles" have an emotionally reciprocal relationship to their host, being affected by and feeding into the host's emotional state. In late chapters, Koro-sensei states that he wanted to be "full of weaknesses, easy to get along with" and able to "touch even the weakest of things, protect them, and guide them". This from a guy who responded to a reckless assassination attempt by threatening the students' families...
Keiichi in early chapters of Ah! My Goddess was highly interested in moving directly into a physical relationship with Belldandy. As the series progressed, this faded until even holding hands was enough to make him blush. Becomes a plot point when it's revealed his sexual urges were suppressed by the Ultimate Force.
Osaka from Azumanga Daioh started out as a quiet girl who was deeply pensive to a fault, and was often made the butt of others' jokes (getting branded with the nickname "Osaka" was one such instance). Within a few episodes though, she made the transition to full-on Cloud Cuckoo Lander.
Kaorin used to be content just to say that Sakaki was "really cool." But in the later episodes her feelings went quite a lot further.
In the earlier episodes, Koyomi was less uptight and even pulled a prank on Osaka. This is quite jarring, given that she was firmly cast as the show's Only Sane Man just a short time later.
On the very first page of the very first chapter of Berserk, we are introduced to Badass protagonist Guts in the boldest way possible: having sex with a hot demon woman. However, later chapters full of traumatic backstory reveal that Guts is not the type of man who is keen on being sexually adventurous with random women, for pleasure or otherwise like killing demonesses mid-coitus and is staunchly faithful to the one woman he has decided to share his heart with. Granted that one would think that this behavior is only typical of the anti-heroic archetype that Guts represented at the time of Berserk's debut, only it's revealed no more than two chapters later that Guts has some serious hangups about being physically touched with a bonus hint of foreshadowing for what was going to be revealed in the flashback arc. So it goes without saying that a lot of fans find the first scene of the manga weird, to the point of disregarding it almost entirely.
During the Soul Society arc, Mayuri was cold-blooded, murderous and evil. There may have been ham, but he wasn't played for comedy. In the Arrancar Arc, he became a CloudcuckoolanderJerk Ass whose ham was Played for Laughs. This polarised the fan base between viewing him as a Karma Houdini that's escaped justice at Ishida's hand and viewing him as pure sociopathic comedy gold. In the Thousand-Year Blood-War Arc, Mayuri's cold-blooded evil and hammy comedy have combined into something that is played for either seriousness or black humour.
Kon was introduced as a threatening character that was then revealed to be a Technical Pacifist (even putting himself in danger to protect some ants). However, once he was made Ichigo's 'substitute' 'soul candy' he was relegated to status of Joke Character.
Code Geass: In his first appearance, Sir Jeremiah Gottwald was portrayed very negatively as an incompetentracist who was easily outwitted by Zero/Lelouch and was generally an unpleasant person. By his next appearance, however, he's managed to Take A Level In Badass and gain a sympathetic backstory as an imperial bodyguard who blames himself for Marianne's death. Moreover, his prior dislike of the Elevens is explained as being due to the mistaken belief that they had murdered Lelouch.He then proceeds to make a Heel–Face Turn, get Ship Teased with the series' resident Ninja Maid and ends up as one of the few characters to receive an unambiguously happy ending.
The rest of Britannia to a lesser extent. In the first season Britannia was completely ruthless and would kill people at the drop of a hat. During the second season this was toned down severely in particular with Cornelia. Presumably this was because the ending would make even less sense than it already did if Britannia was kept the same, and that its previous portrayal made Lelouch seem too justified in all his actions against it, which counters the gray morality he's meant to have (his father and the main ones in charge naturally have to be evil, but to have the whole nation as such is rather ridiculous.)
In the first season, Schneizel looks aghast and horrified when he sees his sister committing mass murder and attempted genocide. In the second season, Schneizel himself does things far, far worse without ever showing a twinge of regret or disgust. Unless something happened to make him much colder during the Time Skip, those depictions don't really mesh well.
It's probably less that the Japanese were being slaughtered and more that he was aghast that it was Euphemia committing the genocide, as she was shown to be one of the kindest and most caring of the royal family.
In Death Note, when Matsuda first appears, he's actually portrayed fairly seriously. He seems to have an Old Cop, Young Cop dynamic with Soichiro, and the very fact that he's at the ICPO conference as his number two certainly says something. It takes a few episodes for his comical Butt Monkey characterization to kick in, although he does occasionally prove to still be competent despite this.
When Vegeta was first introduced, he was a calculating, cold blooded killer who never emoted beyond a Psychotic Smirk and was perfectly willing to sit on the sidelines and let his underlings do all the fighting. Reconciling the overly proud, overly intense, BerserkerBlood Knight who curses like a truck driver and is always ready to fly off the handle for one reason or another that we see later on with that earlier version is a bit difficult.
Future Trunks went from a confident Smug Smiler in the very first episode/chapter to prominently feature him to the deadly serious and occasionally awkward Nice Guy he was better known for being for the rest of the series.
In Fairy Tail, Gray Fullbuster used to be The Rival to Natsu Dragneel, based on their Red Oni, Blue Oni interactions. Gray is now Natsu's Lancer, and they haven't been shown to have a fight for quite while. Similarly, Erza Scarlet was at first shown to scare everyone in the guild, though nowadays that seems to have mellowed. This is even lampshaded by Lucy at one point, when she says that Erza has changed from being completely intimidating to someone who is genuinely easy to get along with.
Several of the hero-turned-villains are like this as well, Gajeel Redfox and Pantherlily most notably. Gajeel started out as a completely sadistic nutcase who beat his Implied Love Interest the first time they met, and Pantherlily was OK with sacrificing a town at his king's whim. Compared to Gajeel's current status as Friendly RivalSixth Ranger and Pantherlily's as the Only Sane Man, their early characterization can be a little jarring to look back on.
Erza mellowing out is actual development. It's her obligatory quirk that changes. During her first appearance she has as poor a grasp on normalcy as Natsu. Later chapters just have her taking everything seriously, no matter how minor.
Erza was also initially suggested to be constantly out on difficult missions like most of the other S class mages and only returned briefly to pick out a new job. She's out on a mission for the first 4 episodes the terror everyone is in while she's around suggests she's not frequently around. Yet after this she's a regular fixture, either part of Natsu's team or hanging around the guild. In fact the next arc has a plot point that she's the only S class mage that's always on hand.
The very first job Natsu and Lucy take is breaking into a rich man's house to steal his property and destroy it during which they beat him and his staff up and destroy his house. A blatantly illegal act. It would later be established that Fairy Tail, and Natsu in particular look down on Guild's that deliberately commit crimes, such as Phantom Lord trying to kidnap Lucy and Trinity Raven's assasinations, and such work is usually done by Dark Guilds. Instead most of their work is "good" like saving people from monsters and such.
You have Saito's Love Interest Siesta who in the first anime season is a good-natured classy women; seen as the complete opposite Saito's main TsundereLove Interest, Louise. Later seasons however, Siesta's character takes a complete 180 and acts more like a desperate slut trying to force her way into the relationship. Some fans say that her desperation was just a change in tactics after realizing near the start of season two that she's failed to win Saito by way of her normal persona. The kicker however, is that you never see the same loveable Siesta from season one again after deciding to change her actions.
Even Saito went through an unexplained change between seasons. Season one, he always stayed calm whenever he ended up in embarrassing situations with the women. Season 2 and on however, he clearly shows a perverted side of himself anytime a women tries to seduce him in some form.
Futaba-kun Change! has a reverse Nabiki example with Negiri, she starts off as a out and out Barnum with a serious Money Fetish who is quite willing to risk burning to death in a blazing building for a cheap deal but quickly changes into a pretty nice (although still financially shrewd), helpful, and friendly character.
For most of Fushigi Yuugi, Nuriko is a brave, funny and extremely likeable warrior. So it's really strange to look back at the early episodes where he acted like a psychotic, possessive yandere about Hotohori, even going so far as to nearly drown his rival Miaka. And that's not even getting into the Suddenly Sexuality situation later in the series...
Ghost in the Shell's Major Motoko Kusanagi has changed significantly over time; in the early run of Shirow Masamune's graphic novel, she was professional but prone to violent anger, greed, and laziness (when it's funny), but as the series got more serious, became more introspective and solemn. In Oshii's film, she's an independent, solipsist Emotionless Girl, and Ghost in the Shell: Stand Alone Complex balances between the two with a stone-faced stoic professional who has occasional bouts of emotion or poignant introspection. All three versions each take place in Alternate Continuities though, so there's nothing saying that her characterization had to reflect upon her previous incarnations over time.
Batou goes through a similar treatment over the various versions. In the manga, he is often used as a Butt Monkey of sorts when the series exposits various details about the world it takes place in- mainly in regards to how prosthetic bodies work- but he also had his own sense of humor, not above making a wise-crack here or then, even in the middle of combat. He keeps this for the most part, even when the story turns serious. His relationship with Motoko pretty much stays as a purely platonic friendship. The movies turn him totally straight-laced serious and professional with his career, though he still shows concern for Motoko's well-being, which becomes a form of unrequited love towards her, and itself causing him to lose focus on his job in the 2nd movie because Motoko had pretty much disappeared from his life. Stand Alone Complex balance out the two. Batou still has his sense of humor, but he stays completely focused on his job. His humor is toned down a bit over the course of the first season. He becomes a bit more jaded after what happened with his personal hero, the Tachikomas, and the importance of the plot. The dire seriousness of the plot in the 2nd season pretty much forces him to fore-go it altogether. His unrequited love towards Motoko also becomes far more pronounced, but Motoko is aware of it, and shows many signs that she does appreciate it.
Golgo 13 used to be more expressive and sloppy in early stories, before becoming the meticulous Cold Sniper he's better known as.
Hellsing, Alucard at the beginning was business-like and had strong "humane" morale beliefs, thus it's very jarring to see him being the Ax-CrazysociopathicNominal Hero that we best know him as later on.
InuYasha: Most fans know Inuyasha's Aloof Big Brother Sesshomaru as a StoicPerpetual Frowner. In his first appearance in the manga, however, he was smug, cruel, sneered a lot, and enjoyed openly mocking and insulting Inuyasha rather than simply treating him with dismissive disdain.
This is the only explanation for Koga. He starts out as a straight up villain, setting his wolves on Rin's village and killing her, kidnapping Kagome and threatening to kill Shippou. After a brief arc, he mellows out into an Anti-Hero rival to the main character and no mention of this previous deeds is ever made. It's rather jarring that Inuyasha or Sesshomaru haven't hunted him down and killed him, seeing as how he'd hit their Berserk Button and they've killed demons for less.
In Part 4, "Diamond Is Unbreakable" , initially Rohan is portrayed as being reclusive, extremely rude, and possibly even mentally unstable. As time went on, those traits got toned down considerably to where he seemed more eccentric than anything else. He almost seems like a different character in the one-shots compared to how he seemed at his first appearance.
In Part 5, "Vento Aureo", Buccellati was first seen with a relaxed and sadistic attitude (possibly to lower Giorno's guard and intimidate him) only in his debut arc when he was investigating Giorno for the death of Leaky-eye Luca. Afterwards he had a very serious and unflinching demeanor throughout the story.
For a good while in Kenichi: The Mightiest Disciple, Kenichi's masters were eccentric men (and one woman) who often causally talked about teaching Kenichi various lethal techniques and easily suggesting that he just slaughter his opponents. Then, just before Yami entered the picture, Kenichi's masters suddenly switched to Martial Pacifist experts in Katsujin Ken, just so that they could have an ideological divide that would set them apart from the future bad guys. Right from the very start, Kenichi himself had honorable intentions to learn martial arts, and never considered to or wished to use it for lethal purposes, so the characterization his masters were given to set them apart from the antagonists wasn't a big deal.
Lupin III: an enforced example of this trope. Pop Culture has established a certain view of Lupin the Third that is radically different from his original presence. Adaptations of the series with Origins Episodes make it a feature of everyone's Character Development to move from their Manga counterpart to their Pop-Culture counterpart.
Were one to read the original Lupin III manga, they'd probably collapse from the shock of seeing how different Lupin was. The original portrayal of Lupin made him a cold-hearted bastard and the goofy demeanor was mainly an act; he'd be more likely to seduce a woman and then kill her after he had his way with her. The subsequent anime adaptation transitioned into a Lighter and Softer approach and turned him into a lovable goofball with a heart of gold, and that portrayal has pretty much stuck since for the most part.
In Magi – Labyrinth of Magic, a lot of people tend to forget that Ren Kougyoku had a completely different characterization in her introduction where she was portrayed as an Alpha Bitch that looked down on anyone that she saw as disgusting; even to the point of brutally beating down Ugo until he was forced to leave Aladdin's side forever. It wasn't until Sinbad stepped in that her more "likable" side took over, and became the Shrinking Violet / Tsundere mix that everyone views her as nowadays.
While a lot of the changes were planned well before the first manga episode was published, to ease into the intended story, the author's notes show some characters were significantly altered during the planning process. While Evangeline was always intended to become Negi's teacher, she wasn't originally a vampire or older than Negi - just a trained magic-using assassin with a family grudge. Evidently she got carried along with the scope of the plot.
Early on in Mitsudomoe, Futaba is just as resentful of her father as her other two sisters. Later chapters show that she's the only one who will openly say that she loves her dad and means it, perhaps too strongly. The anime actually brought Futaba's first onscreen moment with her father in line with her later characterization.
Char Aznable: In most of Mobile Suit Gundam, he desires vengeance against the Zabi family, coupled with a Zeonic victory in the war, because of the memory of his father, Zeon Deikun. However, he never seems to take his dad's ideology too seriously. The experienced Gundam lover will search the original series in vain for Char's trademark ideology: that human life on the Earth is parasitic and an abomination to our holy mother, and that the Earth should be rendered uninhabitable to force people into space and further evolution into Newtypes. Almost from the start of Mobile Suit Zeta Gundam, Char begins preaching this ideology of his dad's like he's believed it all his life.
Mobile Suit Gundam Wing's Heero Yuy started out the series as a guy who would laugh like a maniac when shooting down his enemies, and was also suggested to be some kind of superhuman. All of this was quietly forgotten after a few episodes, and Heero switches to The StoicHitman with a Heart who is highly trained and tough, yes, but to much more believable levels.
The laughing while slaughtering enemies comes off as even more unusual when you get to Mobile Suit Gundam Wing: Endless Waltz and see his accidentally killing a little girl and how it drove him to attempt suicide in penance, as well as his overall war weariness that leads him to declare, in his last line in the movie, "I don't have to kill anymore. I...don't want to..."
Asahi's defining point in the early chapters was his inability to keep a secret, a trait which eventually got phased out in favor of treating him as the Only Sane Man. In fact, several of the other characters are worse liars than he is.
Akari started out as something of a generic teacher with no real quirks other than being rather acerbic. Later chapters gave her a love of alcohol and a major complex about her status as a Christmas Cake.
Shimada was largely a normal (if somewhat jerkish) guy at the beginning the series before eventually being turned into a Jerk AssCasanova Wannabe who's such a pervert that there's a Running Gag about him getting arrested.
A minor one regarding Rock Lee. His first appearances, he's clearly crushing on Sakura as he attempts to ask her out and adamits his feelings towards her. This plotline then fades into obscurity afterwards with only reappearances in Filler episodes. Most fans however believe that Rock Lee got over his crush overtime, even if it was never truly explained in the manga.
The 1st Hokage. From his reputation and appearance the 1st time Orochimaru revives him, he seems like a stoic, serious warrior. When he is later revived (along with the 2nd-4th Hokages), it's revealed that Oro had been suppressing his personality and he's actually a rather jovial, enthusiastic, even somewhat goofy guy akin to an older Naruto.
The Kyuubi/Kurama of all things, has become a Brilliant, but Lazy, TsundereTroll, which is jarring to when he was as monstrous in personality as he was in appearance, trying to leading Naruto down the Despair Event Horizon in order to one day be set free to cause more chaos.
Before the start of the Final Arc, Black Zetsu is shown to be a loyal servant of Obito Uchiha as shown in several scenes before along with him apologizing to Obito when he is forced to use Rinne Tensei on Madara. But once the Final Arc kicks in, he is shown to as callous as Madara and berates Obito for ever daring to betray Madara's plans. This even culminates in him betraying Madara and Retcon him from a will of him into a will of Kaguya, with no foreshadowing whatsoever.
Although the cover story focusing on him shows this was a gradual change; at first, Hatchan is very quick to abandon Camie in exchange for a map leading to a Takoyaki recipe.
Similarly, Ace was introduced as being polite and cheerful, even when facing off against Marines, and to an extent, Blackbeard. The Impel Down and Marineford arcs, as well as Luffy's flashback on the two meeting each other paint him as having picked fights with people who spoke ill of his father, Roger and questioning the value of his life, which would potentially suggest that the way he was shown acting before was a facade.
His hotheaded nature was foreshadowed during his cover story, when he blows his cover in a Marine base by punching out a Marine who talked smack about Whitebeard.
Considering his legendary ability to get lost, it's a little odd during the Captain Kuro arc that Luffy's the one who gets lost on the way to the battle, while Zoro's only delayed by a slippery hill. It's even more odd in an earlier arc, where the anime adds a joke where he points Luffy in the right direction to charge in. Let that sink in: Zoro is telling someone else they're going the wrong way.
In Zoro's case, this trope is invoked due to greater diversity in the crew. When it was a two-man outfit, he was the Only Sane Man, very much so in comparison to Luffy, but as the crew has gained a greater balance of sanity (namely through Nami and Robin, as well as Chopper and Usopp when the situation calls for it), he started becoming quirkier. Much the same goes for Sanji, who has not lost his original competencies, but has had less need to use them as more down-to-earth crewmates were added.
Trafalgar Law was initially introduced as a Perpetual Smiler who was generally laid-back unless people tried to order him around or attack him, though he did have a creepy edge. He's a little more focused in his next appearence, though he was doing emergency surgery for that so it's justified. After the timeskip, he's incredibly serious and almost a Perpetual Frowner, smiling only when he's got an opponent where he wants them.
Ash Ketchum has gone through quite a bit of change, as well as quite a bit of reversion, since his start in Kanto:
Although Ash is quite clearly either Asexual or a Chaste Hero in most later seasons, in the early Kanto season, during one of the episodes, Ash had a small crush on a girl and found her attractive....until she began talking down to him, after which his interest faded.
Ash pretty much goes through a complete character re-haul when the Unova series comes around. He was portrayed as a stupid newbie for a good portion of the original series, but gained a sense of maturity throughout the Advanced and Diamond and Pearl series (though still blissfully immature in aspects like his Hot-Blooded battle-lust or obliviousness to love.) Once Best Wishes started up however, the maturity is dropped, and he's suddenly a complete idiot who even surpasses his original series incarnation. Conversely, in XY, he's gained that maturity back with interest.
Even said obliviousness to love was a later addition; back in Kanto, he knew enough about mating and love that when Butterfree wanted to leave the group to mate, Ash understood why; compare even to Advanced Generation, where he thought his lovesick Grovyle was suffering from a fever.
While Pikachu eventually came around, he initially thought that Ash would get him killed. Pikachu would shock Ash deliberately when upset, until at least Celadon City. Now, they're inseparable.
In his first appearance, Brock was the calm, mature (if not somewhat cocky) gym leader of Pewter City who took care of his younger siblings and who recognized Ash as an inexperienced but eventually worthy opponent and wished him well on his journey. Soon enough after deciding to join Ash, while some of his past characteristics remained, for the most part, he was badly flanderized into a immature, horny and love-sick dork who even went as far as to be willing to give up his travels, his goals and his two close friends just so he can be with a girl who clearly has no interest in him. The worst example of this was his decision to be with Professor Ivy and left Ash and Misty to fend for themselves just so he can "learn more from her."
In the first few episodes of Best Wishes, Iris was seen to be very extreme and rude. But this would prove very grating if continued, thus after Cilan joined up, she suddenly becomes rather behaved, and her wild tendencies were suppressed to focus on the humorous Small Name, Big Ego/Cloud Cuckoo Lander aspects of her personality, and while a Deadpan Snarker, she mostly keeps the quips at her friends' expense to herself rather than be openly rude or antagonize them. Her Cuteness Proximity habit also faded almost entirely and transferred to Bianca instead.
Ash's main rival Trip has also changed drastically from his first two and a half appearances. He was at first a overconfidenttrainerwho talked down on Ash and his region but mellowed out halfway through his third appearance because of a smackdown that Burgh gave him. Appearances after that have him very quietand distant and more annoyed at Ash for his crazy antics (who would blame him?), but hasn't tried to actively antagonize Ash or talk bad about his region since. Some people (mainly Paul's fans) refuse to see the change and only comment that he's just a plain Jerkass like in his first two and a half appearances.
In the earliest episodes Meowth acted very cat-like, walked with a catlike gait when on two legs, and sometimes walked on four legs. In the English dub, he also had a more catlike voice before switching actors and ended his sentences with a Verbal Tic (he uses one in Japan, but it didn't translate well). While still not exactly a formidable fighter, Meowth has also become slightly braver and more cunning towards physical combat. He usually cowered before Ash's Pokemon when it came to actual battle, in one XY episode he is so incensed with being outdone he demands a fight from Pikachu, even getting in a small bit of damage.
Jasmine was originally more like her game counterpart - meek and quiet - but by her second appearance she became quite headstrong and confident.
Green (Blue in the US version) changed in personality early on. Originally he was arrogant and aggressive like his game counterpart, though after an appearance or two he mellowed down into more of The Stoic.
Much like Ash's Pikachu, Red's Pikachu (Pika) was a Jerk Ass who hated Red at first. Aside from his first chapter his aggressive side is never referenced and he became a generically nice Pokemon and one of Red's favorites.
When Red met Misty he blushed at her and there was some Ship Tease between them. After a few chapters Red becomes a Chaste Hero who is Oblivious to Love. Misty is presented as having unrequited feelings towards him.
In early Ranma ˝ Kasumi is a largely typical but slightly snarkier Yamato Nadeshiko rather than the over-the-top parody example she would later become, and Nabiki is a normal teenage girl and it is even commented on that she is boy crazy before her misanthropic Money Fetish takes over.
Ginei Morioka of Rosario + Vampire is a total pervert and annoying, but he's genuinely kindhearted, a trusted friend and values those close to him more than anything to the point where risking his life is nothing....which is why seeing him as a manipulative Jerk Ass who outwardly threatens to make the heroine his 'woman by force' can be really, really strange. Likewise with how outright murderous Mizore and Kurumu can be at their intros.
Rurouni Kenshin's Hajime Saito is well known as the cold, sarcastic anti-hero who views himself as a (very sharp) instrument of justice. But when he first arrives on the scene he's portrayed as a blade-licking psychopath who can barely keep his murderous urges under control.
Minako from Sailor Moon is unusual in that she actually goes through two different personalities before hitting on her final one: In her original manga Codename: Sailor V, she was a ditzy, emotional heroine type character based on the author herself. However, when the publishers asked Naoko Takeuchi to make Sailor Moon, she gave Usagi that same basic personality as well. This would've been fine if Sailor Moon was a re-telling or alternate universe to Sailor V, but later episodes had Minako enter as part of the Sailor Senshi. This created a difficult problem: how to write Minako to distinguish her from Usagi? At first, the show sort of played on her competent veteran nature, playing her as more quiet, mature, and cool than the others. However, they never really took it that far, and by season 2 when Usagi had another angst subarc to herself, she'd fizzled down into a blank slate with not much more to her than a weird Running Gag about her quoting phrases wrongly. Finally, partway through R they came up with the personality she'd stay with for the rest of the series: a ramped-up version of her original personality that took her ditziness up to outright Cloud Cuckoo Lander levels.
Note that this applies mainly to the first anime. The manga keeps her cool-headed leader traits intact, blending them with a touch of Cloud Cuckoolander.
In Sekirei, Mikogami Hayato is significantly different between his first appearance and all later appearances. In his first appearance, he's a sinister Classic Villain that tries to kill Takami and capture Kusano by force. When the Sekirei he sent to retrieve Kusano is defeated, he declares her "useless". Since then, he's been consistently portrayed as a Cloud Cuckoo LanderFair PlayAnti-Villain that lacks in standard morality, but genuinely cares for his Sekirei. This can make comparing his later sympathetic portrayals to his portrayal in the "Green Girl" arc fairly jarring.
Crayon Shin-chan: Nene used to be scared of her mom when she vented her anger punching her plush bunny, prompting Nene's Catch Phrase "That's not my usual mom!". Not that you would imagine now she does the exact same, though at least this was given a plot reason instead of randomly changing. Also, for some reason Nene's mom punched a teddy bear at first, instead of her iconic Happiness Bunny mentioned earlier.
Slayers: As time passes in the anime version of the story, either this or Flanderization occurs to virtually all main characters to some degree for the sake of comedic effect. Poor Gourry the swordsman is a pretty notable case because he began, in the anime, as a somewhat dim-witted and tactless yet competent swordsman who could point out the less obvious details in certain situations. Unfortunately as the story went on, he didn't change characterization so much as he became nearly completely defined by his poor memory, swordsman skills, and role as Lina's "guardian"/occasional Living Emotional Crutch. It doesn't help that of all the characters, despite being the second most prominent, he has the least explored backstory, and the only information about it has been given through Word of God and a single novel released only in Japan. By comparison, novel!Gourry, while still tactless and selective in what he chooses to remember, is clearly in certain situations merely Obfuscating Stupidity to mess with people.
Lina Inverse is known for having a Hair-Trigger Temper, insulting others, and a penchant for Greed. If one goes back to the first anime season (or reads the novels for that matter), they would be surprised that Lina's temper is no where near as short as it had become, that she was something of a businesswoman (as opposed to resorting to bribery), and showed signs of sarcasm and sharp wit.
It can be a little odd going back to episode 2 of Soul Eater, where Tsubaki is not only frustrated with Black Star but snarks at him and throws ninja stars at him, considering her rather... large amount of patience with him in the rest of the show.
Between Soul Eater and its later established prequel Soul Eater Not!, there are quite notable differences between Jacqueline's personalities. In Soul Eater, she was introduced as being the least quirky of the secondary cast, and can be easily described as The Stoic. In NOT, she's quickly established as being a good yet strict student, easily embarrassed, and is heavily implied to be attracted to her meister, Kim. Note that even though NOT is a prequel, it was written long after her first introduction and she's never shown to have these characteristics in the original series.
Chief technician Shiro Sanada in Space Battleship Yamato (called Sandor in Star Blazers) was originally just the Smart Guy of the Yamato. Sanada rose in status to being the elder spokesperson of the crew, especially after the deaths of Captain Okita (Avatar) and Chief Engineer Tokugawa (Orion), and someone who could be a captain in his own right. In Yamato Rebirth, Sanada actually becomes the head commander of the EDF, now outranking his old captain, Kodai (Wildstar).
The Prince of Tennis: Atobe in the beginning is seen as quite the smug Jerkass when he tries woo An Tachibana. While he does retain some over-the-top arrogance. subsequent scenes establish him as someone who cares very much for his teammates and his rivals.
While the titular character of Toriko has always shown to be rather self-centered, the downright callousness he shows Komatsu is an early arc is jarring. Komatsu gets killed because Toriko forgot to warn him that the crackers he gave him were in fact bombs. Komatsu only lives because of a friendly old man Toriko earlier gave booze to (and the old man would've had his own to begin with if Toriko hadn't bought it all for himself), and afterward Toriko is all, "You died? Oh well, good thing you're alive again!"
The anime fixes this by Komatsu being given the earplugs right away along with the firecrackers (though he accidentally drops them at a critical moment, forcing him to use one without them). Toriko also shows more relief that Komatsu is safe when he and Coco find him.
In Urusei Yatsura, Ataru didn't start out hated by all girls and Shinobu, Benten, and a one-shot named Oniko showed some attraction to him. He was genuinely interested in being faithful to Shinobu, and was excited to marry her, in contrast to his later fear of commitment.
Oyuki also expressed interest in Ataru when she first appeared and seemed to hate him less afterward. Ataru, while still very much a pervert, was less stupid and a bit more on the cynical side in early Urusei Yatsura, more Book Dumb than just dumb.
Shinobu's fiery temper and super-strength were not very significant in early Urusei Yatsura chapters, while the anime changed these appearances to bring her up to date with her later characterization.
Megane, leader of Lum's fanclub was willing to chase after other girls, but later on was show to freak out when he was attracted to someone other then Lum.
Wandering Son has a justified version. Chiba was originally a normal, if a bit odd girl. She was sweet and cute girl, who likes cute things and feminine boys. Chiba wasn't that unusual from rest of other cast. She changed after a stream of bad things happening to her such as a rejected Love Confession, an argument with her friend Takatsuki that made them hate each other for a while, and generally feeling she was putting pressure on her friends. She became a bitter, depressed, pre-teen with a sarcastic streak, her appearance became more mature, and she's generally angry. She's since mellowed down though and has become more like her original personality too.
Less justified in Sasa's case. In the first few chapters she didn't have a concrete character or even a name so she's taller than she should be and lacks her The Cutie personality.
Thanks to character development thia happened to Takatsuki and Nitori. Introduced as a confident girl and a quiet, sensitive boy by the end of the manga they had changed a lot. Roughly 8 or 9 years have passed, with Takatsuki's confidence being more fickle and Nitori being the more decisive of the two.
Rin of Yes! Pretty Cure 5 was originally supposed to be a shopaholic despite her tomboyish personality. This was completely phased out. She does, however, retain the jewelry design dream that goes against the same stereotype.
Initially the villains would be assholes who just happened to act mean spirited to the heroes while forcing them to play a variety of games that were rigged in their favor; fast-forward to the sadistic minions of later Big Bad Pegasus, Marik, etc., who would prolong suffering while being extremely smug and overconfident.