Motoko Kusanagi seems to have had a breast-size-upgrade between The first season of Ghost in the Shell: Stand Alone Complex and SAC: 2nd GiG. She also started to wear pants, around the same time, so this goes both ways. She gets a new body near the end of the first season. It's the same body model that she was using before, and she mentions that because she's working for the government, it has modified specifications well beyond standard legal limits. This basically means that she actually gave herself a Fan Service Pack. Her roommate Kurtan is sexually aroused by this.
Also on meta level, her appearance in Mamoru Oshii's movie her appearance was heavily built and utilitarian with almost masculine facial features and her personality is cold and asexual. Stand Alone Complex gave her a sense of humour and occasional flirty moments, although this is in fact closer to characterisation in Masamune Shirow's original manga.
Though it was in the outfits only, several of the seven surviving members of the Northern Campaign in Claymore went from the skin-tight but fairly conservative Claymore uniforms to black uniforms that flash a bit of thigh post Time Skip, and along with a few skirts one basically wears a leotard and no pants with Zettai Ryouiki.
Nami from One Piece slowly developed her rack from modest beginnings into a set the likes of which most real women would be hard pressed to match. She also lost a considerable amount of girth from her waist and widened a bit in the hips. Word of God states that this is because she is a maturing young woman...which doesn't explain why her breasts have been so inconsistent, varying in size widely (although generally gaining in mass on average) for the last number of years. The Movies generally up the Gainaxing and shoot for the largest chest size they can get away with.
This was most apparent in the seventh movie, where Nami and Robin both gained 2 cup sizes that apparently made their breasts defy gravity, as their bouncing was so out of control they bounced up no matter in what direction any slight movement was made.
In Mahou Sensei Negima!, it isn't so much that the characters are getting more attractive, so much as we *cough*see more of them as the series progresses. The girls get more and more excuses to dress in casual/fetish clothes. Yuna explicitly undergoes a growth spurt, which becomes the source of a large amount of humor later on.
A variety occurs in Kamichu!, where Matsuri becomes a lot more well-endowed in the manga that was based on the anime, in line with the overall enhanced fanservice.
Near the end of the Ranma ˝ manga, Akane — whom the other girls, Ranma included, consider flat chested, even if it's just by comparison — is very happy about having grown up. She doesn't even mind if no one else notices, it'll be her secret pride. But then her pride and happiness are shattered when Ranma, who had always been better built, turns out to have grown up too...
Bastard!!'s female character's bust size slowly but steadily increase over time. The later issues have taken this to truly over-the-top heights.
Risky Safety had two episodes where the titular pair turned the story of Momotaro into a Space Opera. During the "story" parts of the episodes, Risky was shown as being a lot bustier than she really is. Not only that, but at one point there were two worm's eye shots of her: one from the front, and one from the back.
Amelia in Slayers: The Hourglass of Falces got a bust upgrade and swapped out her old pants for a miniskirt. The change is so noticeable that before the story begins proper, an Omake has to explain why.
In the beginning of Chrono Crusade, Rosette has a uniform that isn't too unbelievable for a nun — a baggy blue dress that's only lent shape by an ammo belt around her waist, and bloomers that go down to her ankles. However, when she moves up a class in the Order and gets her new militia uniform, her uniform is changed to have her wear a corset and a skirt that's slit nearly to her waist, as well as a short pair of bloomers that might as well be ruffly booty shorts. The anime takes this even further, appearing to increase her cup size and discarding the bloomers entirely for a pair of tight, white panties.
Yu-Gi-Oh!, when she first appeared the Dark Magician Girl was just another female monster, no more attractive than any monster before her and actually a fair bit more conservative than many. By the time of Season 4 though her face is prettier, her body more shapely including larger breasts, and she's acknowledged in-universe as a sex symbol, to the point the sequel series Yu-Gi-Oh! GX made it a Running Gag that Syrus has a crush on her, and an episode revolved entirely around her spirit manifesting during a festival and the entire student body drooling over her.
In D.Gray-Man, villainess Road Kamelot began as sort of a creepy, almost inhuman looking little monster. Roughly 170 chapters later, she's shed some of the more blatant aspects to her design (though kept just enough to still hit that fetish), traded in her dress for a form-fitting outfit, gained features that are smoother and more natural looking, with the result being that a character who was initially pretty disturbing in appearance has ended up really cute.
Miu of Kenichi: The Mightiest Disciple already had large-ish round breasts, but it was at least somewhat in proportion. Then they started to up her cup sizes. By chapter 292, she's bigger than Shigure. By 421, we've gone above and beyond silly sizes.
Freya gains in size considerably over the course of the manga as well. Compare her bustline when she's first introduced to her size in the D of D tournament. Over twice as large.
Most of the younger females in Naruto got this after the time skip. Hinata for example still wears her massive baggy jacket but now she has a very noticeable bust underneath it.
In Fullmetal Alchemist, Winry subtly...gets bigger. Fully justified in that she's a developing teenage girl and the series spans at least a whole year.
Ed also gets taller and more broad shouldered as the series progresses, gradually going from 4'11 to 5'5.. Winry actually takes notice at one point.
Kitty Pryde has always been cute (if sometimes showing dubious taste in costumes) but definitely got hotter over the years. It helped that she was allowed to age over time, gradually going from a 13 year-old Tagalong Kid to a a sexy, confident 20-something. This culminated with her appearance in Joss Whedon's Astonishing X-Men, where she had an unexpectedly risque nude scene and finally got around to sleeping with Colossus after almost 30 years (although in her defense, he was dead for some of that time).
Marrow came by this through artist fiat. Then they did it plot-wise. She's healed from injuries in a Skrull medical chamber and of course comes out that much hotter. Slightly handwaved in that her skeletal structure is very malleable (it's her power) but still.
Rachel Summers◊ started out in Uncanny X-Men as a skinny woman with a crew cut and a penchant for leotards and legwarmers (probably since it was the 80s). After a Wolverine-related injury, she was taken to Spiral's otherdimensional "Body Shoppe" and subjected to a never-elaborated-upon process (the Body Shoppe usually specialized in cybernetics), so that when she reappeared in Excalibur she looked like a porn star and wore a spike-studded red leather catsuit (granted she had a mullet, but to be fair, it was the 90s). She also wore a similar catsuit in flashback (when she was a brainwashed slave of the anti-mutant Sentinels) though that was more a case of Evil Is Sexy/Evil Costume Switch.
Raven in Teen Titans actually started out as a somewhat average-looking superheroine before George Perez decided to give her an excessively gaunt look to differentiate her from the other female characters on the team. She mostly remained this way after he left, save for when Eduardo Barretto drew her. After her resurrection in volume 3, she was revamped as being more conventionally attractive, although that also meant giving her much larger breasts.
Sally Acorn from Sonic the Hedgehog and Sonic the Comic. At first in Sonic the Comic, she was not that hot at all. She was only slightly feminine in the Archie comic at first. Then the new artist changed the character design, making her far more feminine.
Betty Brant from Spider-Man started out as J. Jonah Jameson's mousy, timid secretary, with a tight, short, curly hairstyle, high necklines and loose skirts. However, as the series went on, she became more outgoing and more aggressive, and grew her hair out into a long, sleek bob, and eventually became a tough reporter who wore skimpy necklines and skintight dresses with high heeled boots.
Pretty much the entire cast in the Harry Pottermovies. Justified in that the actors grew up along with the series, but the filmmakers do seem to delight in getting Hermione dolled up, putting Harry in bubble baths, and putting muscle shirts on Ron in the later films.
Live Action TV
Through some kind of time-travel wackiness, Trance from Andromeda went from being a purple alien babe to a scaly, autumn-colored babe. It may have been one of those things to make the makeup easier on the actress. But she was about equally hot in either form, really.
Willow in Buffy the Vampire Slayer. Her wardrobe started off decidedly frumpy, as though she had been dressed by her mom, then became progressively trendier, moving on to cute. This was half Executive Meddling (with corresponding Writer Revolt) and half intentional on the part of the writers to show her becoming more outgoing and so forth as she grew up.
Nyssa and Tegan get one each in Doctor Who. In Nyssa's final story, she announces that she feels feverish and then promptly strips down to her camisole, remaining in that state for some time. According to the commentary track, it was an entirely deliberate piece of fanservice.
Nyssa actually got two. Previously, the fairy skirt of her original costume was replaced with a tight pair of pants.
To a lesser extent, Rory in the new series. As his badass levels increased, he got far more flattering clothes, a liberal amount of hair gel and was put in some very nice uniforms.
Sam and her transformation that started in Season 3.
Detective Sergeant Barbara Havers of The Inspector Lynley Mysteries, despite being played by the gorgeous Sharon Small, spent the run of the show up through series four going around in baggy sweaters and oversized coats, and with very short hair. In series five she shows up with hair past her shoulders and wearing much more form-fitting clothes.
Pam Beesly from The Office, in season 4, after she officially became Jim's girlfriend and pledged to be a more assertive person. She gets rid of the ponytail and wears more stylish clothes.
Djaq from Robin Hood, who starts as a Sweet Polly Oliver with a crew cut and bulky clothes, and ends as a drop-dead gorgeous Saracen noblewoman.
Elliot Reid from Scrubs started as a cute nerd and became a hottie during season 3 due to demands.
The Shield. Depending on which end of the facial hair debate you fall under, Ronnie Gardocki trading in his nerdy mustache for a full-on beard counts.
Meadow Soprano in The Sopranos. To such an extent that her first post-18th episode in Season 3 has her in a bikini.
Gabrielle on Xena: Warrior Princess managed to wear less and less clothing as the series went on. She started in a ankle length skirt and poofy sleeves and ended in a miniskirt and what is essentially a bra. Xena, remarkably, maintained the same basic level of coverage. Which took her from being pretty exposed to relatively modest when compared to her sidekick.
Thanks to Piper purchasing a nightclub in Charmed the sisters all had plenty of excuses to be seen dolled up and wearing fashionable evening wear in every other episode. And that's not even mentioning the amount of Stripperiffic magical creatures they end up getting turned into. The pack actually got subverted in Season 8 since the actresses went to the producers and complained about it so their clothing is a little bit more modest in that season, plus a new Ms. Fanservice is introduced.
Ivy eventually hit her peak in IV, though, because V's outfit is actually less revealing. Apparently the developers realized if they made her even more Stripperific they probably couldn't hold onto their T rating.
In Knights of the Old Republic, The Handmaiden starts out wearing a sensible white outfit that, while being a little tighter than would occur in reality, did cover her from head to toe. Challenge her to a duel, and she shows up in her underwear (Echani tradition dictates fighting duels in the nude, but the game is T-rated).
Turn her to the Dark Side and she'll start going for a slightly goth-ish look as well, which works surprisingly well with her White Hair, Black Heart nature.
In the previous page picture, Sylvanas Windrunner's original model in World of Warcraft was not only incorrect to what she was (millions of players who either didn't read the manual or play Warcraft III were left thinking she were a Night Elf instead of a High Elf), but not particularly sexy. "We can't have this on our undead elf Dark Action Girl", said Blizzard Entertainment and changed her for the better. Now she looks much closer to her Warcraft IIImodel.◊
When World of Warcraft launched, there were only a few dozen High Elves in the game, all NPCs, all of them were fishes out of water in their stories, and Sylvanas was the only undead one. Considering all that, Blizzard probably decided it wasn't worth the trouble to make a unique character model for her at the time. Then the first expansion came, which included a few more High Elves and updated their appearances but Sylvanas was still the only undead one, which might be why she was left with the appearance of a Night Elf. In the second expansion, though, she was getting more time in the main story, so keeping her as a Night Elf would have been really glaring.
Prior to the first Expansion Pack, all High Elves used recolored (and ugly-as-hell) Night Elf models. Some still do.
Sarah Kerrigan received an almost complete makeover in Starcraft II. While she was by no means unattractive in the first game, her overall look was more utilitarian◊, especially as a ghost.
In the second game, her ghost look was changed to look more like Nova, another female Ghost in the series. Her catsuit◊ become more form-fitting and white, and her facial features became softer and more youthful.
Elesa's outfit in Pokémon Black and White was fanservice-y, but still covered most of her body. In the sequels, she has her midriff and most of her legs exposed.
Joanna Dark from Perfect Dark went from looking like this◊ in the first game, to looking like this◊ in the second one. And the second game was a prequel. Maybe she had them reduced for stealth purposes.
The "kitten" is growing up, maybe? In one week of in-universe time?
A more traditional version occurs from Continuum Shift to Chrono Phantasma - Noel Vermillion goes from this◊ to this.◊ I guess some time wearing this◊ will make you less shy.
Not to mention Tsubaki's new powered-up form, Izayoi. Before, and after◊.
Trish from Devil May Cry seems to get bustier with each new game appearance. In the original game, she looked like this,◊ for her reappearance in the fourth game, she looked like this,◊ with a noticeably more buxom bust (moreso in her guise as Gloria◊), and now in Marvel vs. Capcom 3 she looks like this.◊
Lady changed quite a bit physically between Devil May Cry 3 and Devil May Cry 4, growing a couple of breast sizes and shrinking her clothes a couple of sizes too. It would seem that any woman who is around Dante for more then a day gets progressively sexier by default.
With the more recent Final Fantasy games getting sequels, this has started happening in the newer games.
Final Fantasy X-2 has two examples in Yuna & Rikku. In Final Fantasy X, Rikku wears a vest & hotpants, but trades that for a thong/bikini miniskirt combo in the sequel - In fact, her X-2 costume is the image on the Dangerously Short Skirt page. Yuna, on the other hand, goes from a conservatively dressed (Albeit with black bra showing) summoner, to hot pants & an Absolute Cleavage baring halter top complete with the Zanarkand Abes logo hanging there.
Penelo in the sequel of Final Fantasy XII, Revenant Wings, wears less clothing and gets more screentime. Though admittedly she is wearing her Revenant Wings costume in the ending sequence of FFXII.
Nintendo redesigned Tiny Kong from the Donkey Kong Country game series in this fashion. Originally, in Donkey Kong 64, she was essentially a toddler with long twin ponytails, as she is the younger sister to Dixie Kong. In the DSremake of Diddy Kong Racing, she's suddenly a teenager and sports a tank top and some baby blue pants; essentially an alteration of her original attire. This "age-up" is unexplained and she's still supposed to be Dixie's younger sister even though she now looks noticeably older - not just taller, ala Luigi of the Super Mario Bros. - than Dixie (who still mostly resembles a female version of Diddy Kong with blonde hair) .
Coco in the Crash Bandicoot games has been getting a mild form of this. Originally, she wore youthful overalls. Now she wears a T-shirt that exposes her midriff and jeans. Somewhat justified in that she is physically maturing.
Riot Games has slowly been doing this for some older champions in League of Legends, along with replacing some of the outdated looking splash arts for some characters.
In Resident Evil: The Darkside Chronicles Claire's redesign for the retread through 2 gave her a cup size, tightened her shirt and gave her a more plump buttocks. The developer actually admitted to doing this.
Interestingly enough, Azura follows the exact opposite treatment. Her shrines represented her as topless in Morrowind and Oblivion, but she is a lot more covered up in Skyrim.
CPUs in the Neptunia series almost all undergo a level of this when transforming. It goes from subtle (Noire just smiles more and shows more or less the same amount of skin) to overt (Neptune puts on about four years and at least as many cup sizes) to Plutia (who goes from an adorable girl who wears her fluffy bunny slippers everywhere to Dominatrix sex goddess). Considering the girls are all personifications of various game consoles, the trope name can be taken literally.
Uni actually reverses this; she loses some of her height, curves, and bust when she transforms, to the point where another character wonders aloud if she pads her more covering casual dress. (As with many CPU traits, this is a joke on the console she represents. Later, more powerful models of PSP were also slimmer.)
From Tekken 3 to Tekken 6, Julia Chang's outfit mainly involves a top with a body-hugging vest, combined with a very short denim skirt that provided lots of Panty Shots since her very first appearance. Her skimpiest one is her Tekken 4 outfit and of course, as the luchadora Jaycee.
Another literal, if mild, Fanservice Pack occurred in Dungeons & Dragons Online. Standard garb for male and female characters is fully covering, but players can buy cosmetic "kits" that change the look, often displaying more skin. After a recent update, players discovered that familiar NPC hirelings had started wearing them as well.
Dave Davenport from Narbonic is a male example, starting off as very dumpy and unattractive before growing progressively more handsome as the comic progressed. For comparison, check out the left (earlier) and right (later) pictures in Dave's official bio.
Ellen "Elf" Foxworthy, from Schlock Mercenary, was made much more obviously feminine, as part of an infiltration of a "power makeover" reality TV show. The show only did her hair, make-up, and outfit (which she didn't keep) while the actual body-mods were her own idea beforehand (after being reduced to a head-in-jar they were going to clone her a new body and she requested a few modifications). She added a few cup sizes and at least 6 inches to her height. She's first spotted by the make-over show while out shopping for new clothes since none of her old stuff will fit her new body.
It didn't take long for her to get "upgraded", but Zoe from Sluggy Freelance was originally very plain-looking.
In PvP, after Francis and Marcy have sex, they "level up" and become three years older. As part of her next experience level package, Marcy gains "Hips and boobs", though her newly enhanced physique gets toned down in subsequent installments.
One of the characters in Khaos Komix, Colin, got a reboot after a few pages. His original design resembled another character, Tom, a bit too much for comfort. The artist edited his previous images with his new design, though it looks somewhat awkward.
Inverted with Angelika and Julie in Our Little Adventure. By the time the group reaches Autumnson, Angelika already switched to a more conservative and Darker and Edgier costume switch that no longer has her baring her midriff and showing off her naked legs. Julie follows the same route after they enter the city. This is possibly justified due to Summer being over in the story, and it's not as warm out.
Marigold in Questionable Content. She starts as a stereotypical skinny, flat-chested unattractive gamer-nerd in her first few appearances. She quickly lost that look, becoming almost the complete opposite, being kind of chubby (with obvious pudge), a decent sized rack, and being over all moderately attractive to most fans (and in-universe characters).
The Nostalgia Critic went from a typically lazy, chubby, kinda old-looking nerd who didn't know how to dress himself to someone who is actually quite well put-together. Bear in mind that we're not talking about his sanity.
Foxxy Love in Drawn Together had permanently erect nipples in Seasons 2 and 3 (in Season 1 they were erect only in tense moments)
After the incident with Asteroid M in X-Men: Evolution, Mystique ended up changing from her comic outfit into a leather crop top, miniskirt, and matching high-heeled boots. There are a few who might think she was better before, or that each form had its ups and downs.
In the first two seasons of ReBoot, the animation studio was rather limited on how much of Dot Matrix was shown - both due to technological limitations and Executive Meddling on the part of the ABC network. Then season 3 rolled around... Heck the first episode of the new season had Dot dressed up as Elvira just to show this off.