Hello, I'm Jeremiah Gottwald. I'm so awesome fan uproar brought me back from the dead. I'm made from 100% fresh-squeezed LOYALTY. You can call me Orange.
Most anime are well-known for their Loads and Loads of Characters, especially when they are Long Runners. Sometimes those characters weren't meant to be all that special, and sometimes, they can't even be considered part of the main cast. Whatever the case, they ended up fan favorites.
Matt from Death Note has a huge amount of fans despite only appearing for a few panels. Also Naomi Misora, who got a spin-off prequel novel focusing on her. Beyond Birthday, the villain of that novel, is also an Ensemble Darkhorse.
In Digimon Xros Wars, Blastmon is essentially a fan-favorite. His child-like behavior, his nonchalant approach to his duties, and his Large Ham way of speaking made him an instant favorite.
Speaking of Digimon, Wizardmon in the original was one of two intriguing antiheroes in a show where only incompetent comedic characters had previously been allowed to straddle the line between good and evil. The other, Gatomon, was hit with Redemption Demotion pretty hard, but Wizardmon died too quickly to lose his awesome. (It helped that he was very well-voiced by Robert Axelrod in the English dub.)
Jeremiah "Orange" Gottwald from Code Geass (pictured above) is one of the poster boys for the Ensemble Darkhorse. Initially little more than a racist minor villain, the soul-crushingly humiliating way in which Lelouch bests him turned him into both The Woobie (or the Chew Toy) and an Ineffectual Sympathetic Villain - with a fan-following big enough that the producers rewrote his entire storyline, preemptively sparing him from an ignoble early death and having him eventually turn into an major antagonist for Lelouch who ties into the Geass mystery plotline, then goes on to level grindin badass, pulls a Heel-Face Turn and eventually gets one of the happiest endings. His first full appearance in the second season even seems to include a tip of the hat to the fans, as his last line of dialog seems to be directed more at the viewers than the person to whom he is speaking. This was picked up on by the English dub and he was voiced by fan favorite Crispin Freeman, who delivered that Reality Subtext line perfectly.
It may be hard to remember, but Ohgi was originally something of a fan favorite amongst the Black Knights, being a Voice Of Reason and his belief in Zero as lampshaded at the end of the Narita battle. This was all of course before he stage dived into scrappydom the following season after several rash decisions culminated in the betrayal.
One of the few Black Knights who have remained on the good side of the fickle fandom is Shinichiro Tamaki, Zero's #1 fanboy. Tamaki dodged either death or serious injury so many times that fans eventually warmed up to him and were ready to mourn the guy when he faced Suzaku. Once again, Tamaki's luck didn't run out and he lived to talk about it, so his fans rejoiced.
For being characters that serve little purpose other than to look cute and die quickly and unsympathetically after less than a minute's worth the screentime (or less than 5 seconds in the case of the former; see: mooks), the Valkyrie Squad and Monica have more fan art than many of the other female characters that are relative mainstays.
Part of this may be due to their minor but significant role in the novel: serving as Cornelia's squad-girls in combat, they're also used to provoke discussion with Cornelia, doing a great deal to flesh out Cornelia's nature. It may be because of being popular from this appearance that they were permitted to appear in the animation at all.
We have several from GaoGaiGar; Mic Sounders the 13th (to the point where he was the only survivor of his Red Shirt Army brothers), HyoRyu, EnRyu, and Volfogg too.
Invoked in Redline. After two contestants for the title race drop out, for fear of being shot at, JP is immediately voted in. Firstly, because of his epic and Improbable Hairstyle. Secondly, as the only modifications he adds to his Cool Car are an escape pod (well, that only appears in the 2nd part of the movie) and a booster system that makes most speed powerups in video games look like baby aspirin, the odds of him just surviving in a race full of cars mounted with every weapon under several suns are 25000 to 1. A mafia type group exploits this little fact through race fixing by having him stay in last place until the final quarter of the race, then rocket up to pole (by which more people will bet on him) and then have him lose.
Inuyasha: Despite being a one-shot antagonist early on in the series, sultry Yura of the Hair became a fan favorite even though her role was only a momentary one. With an stripperific outfit like she has and her attractive human appearance on it's no wonder.
Another person getting an upgrade during Sinnoh was Ursula; a one-shot opponent for Dawn's 4th contest ribbon. After going through a good portion of the Sinnoh journey, one flaw fans always brought up about Dawn's contest journey was that she didn't have any rivals that wasn't all friendly towards her. The one-off character Ursula however, happened to be a Jerkass opponent which people, after lookin back at older episodes, enjoyed about her character since it was the closest thing to a non-friendly rival Dawn has had so far. Her popularity skyrockets because of this, causing the producers to make her a full-fledged rival for Dawn up to the eventual Grand Festival.
Similar to the Ursula example, Harley somewhat counts during the Advanced era, ascending from a one-shot rival coordinator to a second rival for May. Mostly due to his over-the-top acting.
As far as Gym Leaders go, Byron seems to top the list for his LOVE of defense. Maylene also applies due to people loving her character development during the Veilstone arc.
And now for the Pokémon. Misty's Psyduck, Brock's Croagunk, and Ash's Charizard, Sceptile, MukuBIRD (Staravia, now Staraptor), Buizel, and Gliscor, have all reached this status at one point or another.
Special mention goes to Ash's Infernape who started off as an Ensemble Dark Horse due to his rough background with Paul and people wanting to see Chimchar grow under Ash's tutelage, but delved into Creator's Pet and Spotlight-Stealing Squad territory in the later half of the Sinnoh journey.
Lucario can also be one. In every episode it's a really good fighter, it had a MOVIE with the plot centered around it, is a playable character in Super Smash Bros. Brawl (and is confirmed to be returning in the upcoming SSB for Wii U and 3DS), and the developers of the games responded to this by allowing the player to get their own on Iron Island.
While he got little screen time in the anime series proper (apart from one episode, in full-body armour), the fans really warmed to Mewtwo from his two movie appearances. Also, in the second Mewtwo appearance, a teenage girl Team Rocket agent named Domino became really popular due to how cool and sexy she was.
Ash's newest human companion, Cilan, has garnered a ton of fan appreciation since his debut. Award-winning seiyuu? Check. FABULOUSexpressions? Check. Entertaining focus episodes? Check. Though he has become something of a Base Breaker as of late, so maybe it's a "too much of a good thing" situation.
Perhaps by proxy, Cilan's Unknown Rival Burgundy became very popular before she even debuted.
On that note, while Iris is a Base Breaker, her rival Georgia is hugely popular as well, perhaps for having a developed and interesting motivation and character, her dress sense, and... providing an opposing perspective to Iris. Fans are weird that way.
Somehow or another, Hotaru is one of the most popular characters, getting good results even when being the non-villain sailor to get the least screen time. Could be due to tropes The Woobie, Moe (for which she is possibly the trope namer) or just being adorable.
Thetis, a Monster of the Week from the first anime's twelveth episode, proven to be rather surpisingly successful in the fanbase, mainly because she's actually attractive in both human and monster forms, and she has an implied relationship with Starter Villain Jadeite.
The Remules Pooko/Puko/Fuko the balloon woman from episode 132, mainly due to having more personality than other monsters of the week and was rather attractive when deflated.
Sailor Iron Mouse is one of the most popular Sailor Moon characters on Japanese fanart sites, despite being just another member of the Quirky Miniboss Squad from the final season.
Likewise, Simoun's "ore-onna" Yun instantly became very popular with fans, much to the surprise of the producers, which may have taken a Red Shirt off of her. She later became very important, picking up a Story Arc meant for another character.
Yun's best buds Rodoreamon and Mamiina are also fan-favourites and theirsubplot had many fans even more invested in it than in the main plot.
Zazie Rainyday did nothing of note for over three hundred chapters or in either anime production and just as little background information. That seems to be part of her charm as the extreme lack of information has the fanbase clamoring for any info they can get. Word of God even stated that she wouldn't be getting her story revealed until closer to the end of the SERIES. And then the series ended way too early...
Judeau from Berserk has only a limited role yet he is one of the most popular characters of the series due to his "average joe" stance and his genuine kindness that stands out in comparison to the often assholish main characters.
Other examples include Slan, the female Godhand that often elicits fetish, and Luca, the Hooker with a Heart of Gold of the Convictions Arc with Plucky Girl undertones, one of the few genuinely good characters of the series.
The Republic of AmericaAries has quite a few of these, including the boisterous general Haruka Armitage, flirty upperclassman Chie Hallard, and outlandishly-clothed #1 Otome Pillar Sara Gallagher (the last of whom only appeared in the final three episodes of the main series before being given time to shine in the OVA).
Wholesome Crossdresser Watarase Jun in Happiness!! was so unexpectedly popular that he not only was he given a path in the game, he was the star of the first OAV for the show. In fact, the game was rather bland and forgettable and wouldn't have had much publicity were it not for Jun. The other characters combined don't get as much fanwork as he does.
To a lesser extent, Taniguchi (one of Those Two Guys) also applies, especially after his voice actor's success as an Ensemble Darkhorse on Lucky Star. In fact, Taniguchi and Minoru Shiraishi could be said to be one single, transcendental cross-series Ensemble Darkhorse. One word: "Wawawawasuremono."
Now he has a Character CD coming out for the second season (as well Tsuruya).
Dragon Ball Z: Appule. A weak minion of Freiza who was killed by Vegeta without a fight has nevertheless gained some popularity in the English-speaking fandom.
Bardock should also count since the movie about his conflict with his race's predestined end at Freeza's hands (or rather finger), earned him Canon Immigrant status, and was even said to have almost single-handedly continued the series.
He even managed to survive his death by being sent to the past of the planet Vegeta, where he became a Super Saiyan and killed Freeza's ancestor Chilled, which resulted in the family line's fear of Super Saiyans.
There's also Seripa/Fasha, who despite only appearing briefly in the Bardock movie before her death has quite a fan following, due to being the only named fullblooded female Saiyan in the series for over two decades. She's often featured in a lot of fanart and fanfiction, and even managed to be popular enough to be featured as a playable fighter in the 3rd Budokai Tenkaichi game.
In Dragon Ball Z Abridged, Nappa takes this role. Too bad he only lasts several episodes before Vegeta kills him.
Misao Kusakabe, who started as one of Those Two Guys and whose screentime in the anime amounts to around a total of 15 minutes, has gotten so popular that she had her own figure made, and was given her own Image Song CD! Helped in no small part to her non-animated, more developed roles in the 4-panel comic. Like being the other tomboy of the series.
Bleach: Tite Kubo was very surprised to discover how popular both Gin and Hisagi had become with the fandom. He had designed Gin to be creepy but the character experienced Draco in Leather Pants to a degree the author hadn't anticipated. The author also expressed confusion over Hisagi's popularity given that he was a bit-character with no character expansion and the author felt the fandom was jumping the gun to become so fond of a character they knew nothing about.
Hinagiku Katsura from Hayate the Combat Butler. She is so big an Ensemble Darkhorse, the last popularity poll landed her with a few dozen votes short... Of having as many votes as the ones ranked #2, #3 and #4 combined, those three being the main characters. In the second season of the anime, the entire first ED is entirely devoted to her, and the Relax-o-Vision shots are all fanservice shots of her as well. This from the female support character with the least screen time in the first season.
Athena has been placed here by fans as well, even non-fans agree that she could put contention on Hinagiku for top-spot in the next character polls. And she didn't decide to even show up for 50+ chapters and didn't get serious character development for 150+ .
In the 3rd popularity poll (the first one she was eligible for), Athena came out 2nd with 2168 votes, while Hinagiku won in a landslide (again) at 4089 votes. The other placements haven't been published yet.
Izumi is an interesting case of responding to the popularity. After she ranked so much higher than Miki and Risa, she started getting appearances independent of them as well as an implied crush on Hayate as well as meeting him when they were both kids.
Iruka Umino of Naruto appears rather infrequently, and in fact went without an appearance in the manga (save for appearing on a couple covers) for over four years. Yet he has consistently placed within the top five characters in popularity polls. Iruka hardly gets any screentime, but he arguably makes one of the most important contributions to the plot in that he's the first person to genuinely and openly accept Naruto. Also, the girls like him. Lots. Especially when he shows up with a certain jounin—it doesn't take much work to uncover the phenomenon of kakairu.
Another example in Naruto is Shikamaru. He placed as high as fourth and fifth overall in popularity polls despite appearing no more than any other side character. Perhaps due to this popularity, he is one of the few non main characters to get significant character development and regularly appear post timeskip.
By extension, his father Shikaku and his maybe-girlfriend Temari also get this. Helps that they're both pretty Badass in their own rights - Shikaku's the Jonin Commander of the Leaf forces, and Temari's pretty much the series' most consistent Action Girl. Being easy on the eyes doesn't hurt either.
Naruto also features a character that may well be the ultimate Ensemble Darkhorse: Hayate Gekko, the Ill Boy Jonin with the Incurable Cough of Death. He placed eighth overall in a popularity poll despite his only actions being overseeing the third round of the Chuunin exams, stumbling onto the Sand and Sound villages' plan to invade, being found out, and dying instantly.
Anko is also really popular, despite only appearing in the Chuunin Exam arc before she disappeared from the manga for like seven years before finally showing up again. This is probably why she had several brief appearances and a filler arc in the anime.
The Fourth Hokage is a Posthumous Character who has only appeared in a few photos and flashbacks, yet he has a following of whoa, probably for being the manga's epitome of a BadassBishōnen.
Aburame Shino is a really popular character, despite mainly being in the background. This probably has something to do with the fact that he is Naruto's version of Batman.
On the dark side; Hidan and Kakuzu. They got way less screen time and chapters than any of the other Akatsuki, yet they're still very popular.
Hinata has limited screen-time in the manga, but is still the most popular female character. Then there was the massive freak-out over both her confession and Disney Death. The animation studio are all fans of her and noticed her popularity enough to increase her screentime in the fillers, but this unfortunately made her a Base Breaker due to claims of Creator's Pet at work.
Her sister, Hanabi Hyuga, is also very popular despite only appearing twice in the manga and not having any relevance other than being stronger than her despite being younger.
Fu and Yugito, the female Jinchuriki, are the most popular Jinchuriki after Gaara, Killer Bee and Naruto himself. Perhaps they are just a way to look at a female version of Naruto, perhaps its because one has a flaming cat in her, or the other green hair....
Out of all the antagonists from the movies, The Masked Man/Menma from Road To Ninja is the most popular.
Tobirama Senju, the Second Hokage has became one during the current arc. Doesn't hurt that he happens to be the Only Sane Man and Deadpan Snarker, who has a good sense of humor and is highly intelligent. He also knew what to do with a near Always Chaotic Evil group of people, and has been giving a lot of the spotlight even fighting alongside Naruto, Minato, and Sasuke on the front lines against Obito Uchiha. A few popular memes have been 'We should have listened to Tobirama' with a picture of Hashirama above it, or 'Tobirama was right'.
Tayuya The Sound Kunoichi is most often the popular of the Ninjas from Otogakure shown in fanart or in stories. Most often have her doing a Heel-Face Turn. Being one of the few females in Part One who actually could fight and do stuff probably helped.
Kaiba (to Yugi): Can it, you loser! Do you have any idea how sick I am of your posing?! You're pathetic! Nobody cares about you! I'm the only reason people watch Yu-Gi-Oh! Me, Seto Kaiba! I have all the cool gadgets, I have the all best outfits, and I have all the most powerful monsters! Nobody would be watching this movie right now if it weren't for me, so just this once, I deserve to win!
The easiest way to tell how popular Kaiba was at any point in the manga is how much taller he is than his original appearance. Where he was only tall compared to Yuugi initially, he gradually became taller, darker, and more handsome as time went by.
On a related note, the character Tetsu Ushio, who before was known only as the first person to lose to Yami Yugi in a Dark Game, got a shot in the arm as a villain-ish character in Yu-Gi-Oh! 5Ds.
To top that off, Ushio has now started running around with the main characters as part of the group.
And in the dub, he's voiced by none other than Yami Yugi himself, DAN GREEN!
Team Taiyou, both in and out-of-universe. Everybody roots for the underdog, but Taiyou pulled it off with such aplomb - a group of reasonably-skilled players from the countryside, named for the rising sun of hope, saddled with Decks full of Com Mons not worth their paper and the living embodiment of Awesome, but Impractical for an ace card, riding a D-Wheel held together with tape and force of will. Not only did they match the main characters at every turn through superior tactics and teamwork, but they did so using a Stall/Burn strategy, in a season where Attack! Attack! Attack! was the order of the day. Though the WRGP Arc is often regarded as a sufferer of Seasonal Rot, Taiyou's arc is basically the only thing everyone agreed to be fantastic, with the only common complaint being that they lose.
The card game itself arguably fits this. Originally it was only going to appear once, but the fan demand for it to return was so high that the series ended up being about it.
Considering how popular they are in Ranma ˝ fanfiction, you'd think Tsubasa, Konatsu and Pantyhose Taro were part of the regular cast. However, Tsubasa appeared only once in the manga (and in just one other episode, plus a couple of cameos in the anime), Konatsu twice (never in the anime), and Taro was in just three stories.
Takasugi Shinsuke in Gintama. He's only appeared in a few manga chapters and episodes, he's the only one in the series not to have some sort of hilarious appeal — and he still managed to place high in the popularity polls.
Similarly, Shinsengumi member and badminton fanatic Yamazaki Sagaru ranked high among fans, but creator Sorachi Hideaki has stated he will never be featured on the cover of any of the manga volumes. One can only hope he'll change his mind. There's even A WHOLE STORY ARC ABOUT IT!
And now, Kamui who only has been in one arc has been in the top ten polls ranking at 7th.
Kamui has since moved up to third place in the most recent poll despite only appearing in two chapters during the gap between the surveys.
Tomoyo Sakagami from CLANNAD. She is one of the main heroines (including Kyou, another cast darkhorse) that doesn't have a dedicated arc for her in the anime (unlike Fuko and Kotomi). And the result? A special episode set in an alternate universe where Tomoya ends up with her instead of Nagisa. And then there's the sequel to her Visual Novel route, Tomoyo After...
A second Tomoyo-centric manga named Clannad - Tomoyo Dearest◊ just got released, and said to be taking around After Story, not some Tomoyo After re-interpretation...
Note that Kyou also got her own AU special where she ends up getting with Tomoya.
The reasons why Tomoyo and Kyou don't have an arc in the anime is because their arc is romantic and completely conflicts with Nagisa's. It just wouldn't work even if you have Tomoya cheating on everyone since it would ruin everything, especially "After Story."
For reasons that can't really be explained to outsiders (in part because we don't even quite know), the AKIRA fandom has a good-sized faction of obsessive Kai fans. Despite the fact that he gets about five lines in the film, never becomes more than a minor character in the manga, and most of the more casual fans don't even seem to notice him at all.
Creepy Stalker Mizore Shirayuki is the overwhelming favorite for most Westerners in Rosario + Vampire.The anti-social yet earnest and sincere girl struck close to home for many of the more... socially awkward anime fans. The manga seems to be latching onto this, as an arc in the second season has focused on Mizore, giving her significant character development and a serious storyline.
The driver of the bus between the human world and yokai world has gained much popularity with fans even though he has only appeared a few times. Although he does have an important role, as revealed later in the manga.
Kokoa has also been quite well-received since her introduction, and there's a lot of fan art of her.
In Ikki Tousen, Kan'u Unchou (Guan Yu) has a lot of fan support despite not being the main character, being admitted as the sexiest of the bunch (for a series with that much Fanservice, that's saying a lot), her very sympathetic backstory (especially her Bodyguard Crush on her childhood friend, Ryuubi) and, of course, her status as one of the strongest Action Girls in the series. Even though her character was this close to be completely destroyed through Flanderization in Great Guardians (the third season), her fandom still remained as strong as ever. Being the Generation Xerox of one of the Ensemble Darkhorses of Romance of the Three Kingdoms does help a lot...
Fist of the North Star has a good example in the form of Mr. Heart, the Giant Mook who works for Shin. Despite many of the other colorful martial artists in the series, he got to be a playable character in the PS2 fighter and has been featured as a boss in other games as well. The series as a whole has tons of these, such as the Mad Colonel (who was a design inspiration for Rolento of Final Fight), Rei (who got his own Spin-Off series), and Raoh (who is getting his own series as well and was the focus of an OVA series). Raoh even got the rare distinction of being one of the few fictional characters to have a real-life funeral held for him, in recognition of his incredibly manly death in the series.
Nene Andou, the cheerfully bisexual class representative from Hyakko, is being latched onto by a large group of fans, due to her ability to out-quirk the already very quirky lead characters of the show.
Do you see that... special-looking fish-shaped Gundam on the corner? Fine, take a LOL at it. But look now at its pilot... He's handsome, genuinely skilled, and a rather nice guy all along. This is Hans Holgar of Neo Denmark, the Ensemble Darkhorse of the series, who is appreciated not only by starry-eyed fangirls but by some fanboys who are impressed by how he gives an excellent use to such a special mecha both in his episode and the Grand Finale.
To a lesser extent, there's Fuunsaiki, Master Asia's Cool Horse and gloating platform, who boasts being the only horse in existence to have his own Gundam.
The Nether Gundam has a surprising number of fans, due to being the single silliest Gundam in a show full of silly Gundams, and because it turns into a windmill.
Gundam 00 fans seem to latch on the resident Ineffectual Sympathetic Villain Patrick Colasour, for his non-forced hilarity and amusing misfortunes he suffered, this coming from the 'loser guy' on the enemy side, who won't give much impact to the show. And from the good guys' side, we have Emotionless Girl Feldt Grace, so well loved she generated so many fanarts around her and had a sidestory revolving about HER PARENTS. Oh, and in the interim between the first and second season, she became so popular that fans were hoping she'd inherit a Gundam, here we speak about the deceased Lockon Stratos' Dynames, but this is later jossed when his Backup Twin inherits its successor. Maybe she's not named the most popular female of the show, but when you suddenly have her naked in the newest opening while all she did was just being a part of the Bridge Bunnies... you KNOW she has the dark horse feel on her.
Episode 22 finally shows how their Darkhorse-ness pay off. Feldt starts opening up a relation with Setsuna by giving him flower. Meanwhile, Patrick made a serious comeback, and while still bombastic, seems to have taken several levels of badass as he starts to actually kick ass instead of being shot down when he deploys.
And Patrick not only survives, he marries the woman he's loved throughout the series! Also, Feldt manages to be named the most popular female of the show!
Nena Trinity, especially in Japan, where she was the most popular female character until she fell Out of Focus in the second season and (as mentioned above) Feldt took that position. In America, however, Nena's just as oftenThe Scrappy as she is the darkhorse.
Graham Aker, to the point where he was voted most popular alongside Sestuna himself for the male cast. His various over the top antics, combined with the fact that he was the first in the series to take on a Gundam AND severely damage it while using a much weaker mecha helped accomplish this. In the second season he became Mr. Bushido, which turned him into a weeaboo with a lust for revenge. The fandom wasn't very amused. His screentime was also very reduced. He redeemed himself in the movie, in the eyes of all the fans, and even got a status upgrade to the 6th Ranger before his noble death.
From The 08th MS Team, there's Norris Packard, the Zeon ace who commits acts of awesome whenever he appears in a mobile suit. The other times, he commits acts of heartwarming as Aina's surrogate father, as a mentor to his men and as one of the few sympathetic characters with high rank in the series.
To understand just how AWESOME he is one must understand that he, in a setting well known for the fact that the title machines are virtually invincible, takes on three Gundams, all piloted by main characters, and three Guntanks. At the same time. And wins. But dies in the process.
The first episode of Gundam Unicorn yielded an unexpected darkhorse in an unnamed Stark Jegan pilot, thus far one of the only red shirts to be able to put up a decent fight against the Kshatriya (damn near beating it) and probably one of the few faceless, namelessgoons of the franchise to ever stand up strong against a major named character.
Further, the HGUC manual implies that he was also present during the Second Neo Zeon War and was one of the guys who tried to push back Axis. Man's a hero.
Maybe the writers noticed, because they stuck another awesome nameless goon into the fourth episode, this one piloting a customized Byalant and tearing the attacking Sleeves to ribbons almost single-handedly. This guy has also become quite popular with the fans.
Gundam AGE fans didn't waste any time in latching on to Yurin L'Ciel, a cute, possibly-psychic Tiffa Expy who appeared in the second episode and then vanished. Although the fact that she shows up all the time in the opening is kind of a giveaway that she'll be returning at some point.
And that's just during the first arc. In the second arc, we get Arisa Gunhale, daughter of Flit's childhood friend Dique and another pilot aboard the Diva. Her tendency to make people smile whenever she's on-screen, as well as her hilarious method of getting Asemu out of a funk, secured her spot as a fan favorite.
Gundam Build Fighters has Mr. Ral, a character based on long-time favorite Ramba Ral. Having the same voice actor and most of the same traits as the original character didn't hurt either.
Aila Jyrkiäinen's popularity went off the charts after Episode 10 showed that she was a Not So Stoic girl who had Hidden Depths. It also helps that she's the equivalent of the series' female Newtype lead, who have traditionally been very popular among fans.
Greco Logan also has quite a fanbase for himself (at least moreso than characters of his type usually gain). Not hard to see why, as Greco is a Type 1 Eaglelander who has Determinator traits and pilots one of the most beloved mobile suits in Gundam. In fact, part of the reason Nils was hated early on was because many fans (namely Americans) preferred Greco to be the American representative in the Gunpla Battle World Tournament.
Gundam Seed and Seed Destiny have their own darkhorse in Shiho Hahnenfuss, a female ZAFT Ace Pilot who appears here and there throughout the series, but never speaks. She's assigned to the Joule Squadron and is usually seen at Yzak's side◊ in group shots.
Some of Gundam sidestories are surprisingly popular but three stand out most.
Crossbone Gundam, the sequel to the movie Gundam F91, which probably has the most exposure of any non-animated Gundam, showing up regularly in video games as well as model kit and action figure lines.
Gundam X Under the Moonlight, a sequel manga penned alongside the release of the Gundam X DVD set. Its popularity lead to an extension, quite ironic considering its source material was had its episode count cut due to low ratings.
All of this Gundam, but no mention of the Ensemble Darkhorse that started a trend in the series. I speak, of course, about Char Aznable. He may have been a major character to begin with, and was certainly expected to have his own share of fans, but he is now the most easily-recognizable and Iconic Characters from the franchise.
Not to mention the MS-06 Zaku II. Yes, it's a mecha, but it's a weak grunt mecha that never stands any chance against the Gundam without being painted red and piloted by a masked man. And yet, it is always the second release in any new kit series, usually in the Char Custom colours, coming right after the Gundam itself. They've even added Zakus, and many other Universal Century mecha, to Gundam Seed Destiny, a series with no relation to the Universal Century itself, with a pair of custom Zakus appearing right alongside the main character's Gundam. One of which is, of course, red. And there is always a mecha (sometimes more than one) in the other Universe's that bares a resemblance to the Zaku in some manner.
Excalibur in Soul Eater has become a meme on that imageboard. His legend began in the 12th century.
Stein is also very popular in fandom. The professor is a secondary character
Mad Pierrot of the twentieth episode of Cowboy Bebop has no relevance to the over-all Myth Arc, appeared in all of one episode, and was never spoken of or mentioned again. Yet, outside of the main cast, he is easily one of the most popular characters in the series.
O, Canada. (No, he really doesn't appear with the Allies as much as fanfic might make you think.)
In the LJ based fandom, Bulgaria (who briefly appared in two panels and a very recent anime episode, as a brunet boy who looks a bit like a shorthaired China) and Thailand (recently introduced East Asian male Meganekko) are starting to get this fame as well. Hot-BloodedPrussia is already there, tho.
Prussia, especially War of Austrian Succession Prussia, shows up at incredibly high levels of representation at any event involving Hetalia cosplay.
Scotland. He's appeared once as a reference to England's miserable childhood (not even in person mind you) but is still extremely popular with the western fandom.
Let's not even go into the huge amounts of love towards the mochi with America's face that appeared once or twice in Himaruya's blog, known as "Mochimerica" or "Ameri Blob". It's so popular that the Japanese fanartists often use it as a Censor Box in their porny fanarts involving America.
The Nordics are gaining more and more popularity lately, specially Denmark and Norway.
The Baltic Trio ended up with some element of this, particularly after the strips of Lithuania's scars, Latvia's Yandere potential and Estonia in Bloodbath 2010.
And did you guys forget about Holland? Ever since he finally stopped being The Faceless, the fandom has fallen all over him.
"Herr Stick" and the Flying Mint Bunny, thanks to the dub.
Flying Mint Bunny became popular enough to get a plushified form.
Also thanks to the Bloodbath, Iceland's started getting quite a lot of attention from fans for his unique combination of suaveness, awkward moe cuteness, and Bishounen appearance.
It's a safe bet that as of 2012, a good chunk of the massive cast have become this. And it's pretty clear that Himaruya is also aware of this as well.
In Fullmetal Alchemist, there's Maes Hughes, the friendly competent Badass Normalwhose death becomes an important part of Roy Mustang, still consistently scores very high in popularity polls, even 20 volumes later. Another is Jean Havoc, The Woobie who can never get a girlfriend who isn't a homunculus, and gets paralyzed before helping out the coup with supplies.
Also there's Beam Spam Mc Muppet, also occasionally known as Attenborough. He's mainly known for being the king of the Worf Barrage.
Of course, they both pale in comparison to Guame; The Dragon of the first half.
Joe Asakura in Science Ninja Team Gatchaman was initially not planned to be a major character, and instead would have taken a backseat to Ken, Jun, and Jinpei (who were to be the main characters). The original production art of him even shows that he was to be the third in rank, with Jun being second-in-command, but their numbers got switched last-minute in production. His popularity with fans caused Tatsunoko to make him more of a feature character as the show went on, and extended to the sequel series where the previously "dead" Joe returns with cybernetic enhancements and gets even more screentime.
It seems this popularity may have gotten him into the American port (And soon to be Japanese Expansion) of Tatsunoko vs. Capcom.
One of the earliest examples: Robert Edward O. Speedwagon (you can stop laughing now) from Part 1. Despite the fact that he can't use the Ripple and doesn't fight (Zeppelli even notes that he's more or less useless despite his friendship with Johnathan), he's popular with Western and Eastern fans alike. Must be his Nice Hat (a bowler).
Muhammad Avdol in Part 3 was killed by Hol Horse but his popularity caused a fan backlash so big that Araki figured a way to reintroduce him, Back from the Dead by saying the "fatal" shot only grazed him
The internet meme generation has also redeveloped a love for villain Dio Brando, mostly for his signature special attacks.
Askeladd of Vinland Saga is much more popular then the main character. Thorkell as well, though not to the same extent as Askeladd.
Kyoya Hibari from Katekyo Hitman Reborn! has been voted numerous times as the number one popular character in the series. Not to mention being voted and ranked the third most popular anime character in '08 from Animedia. He's one of Tsuna's guardians that initially had a very small role, only appearing once in a blue moon. However, it appears the mangaka has decided to give him a larger role in recent chapters to please the fans.
On the subject, Nietzsche Wannabe Rokudo Mukuro had become very popular and had been voted many times as the most popular villain (and in a rather recent poll, the third favorite character in the series). The author seemed pretty surprised how popular he had become, and it's very likely that due to this, she decided to give him more screentime by making him Tsuna's very unlikely guardian.
The Acrobaleno Fon's adult form which has only ever appeared on a poster in the manga and the FillerArc of the anime but still managed to rank in the top 20 in the latest poll. Looking identical to a fellow Ensemble Darkhorse probably helps.
Enma Kozato almost immediately had a huge fanbase after his first appearance, even though all he did was get bullied, called a loser and had his pants stolen. Despite this, everyone fell in love with him. He was even assigned the standard Reborn fandom number within just a couple of days.
Squalo ranked number 6 in the sixth popularity poll, rising above Xanxus, who had always overshadowed him in all the previous polls.
Hell, the entire Varia remained surprisingly popular after their stint as the bad guys in the Ring Battles Arc. So much that they were brought back in the TYL arc, with chapters completely dedicated to their battle against the Millefiore in Italy.
Fran has made it to this position, being ranked 4th most popular in the latest poll.
Perona from One Piece has shades of this as she ranked in the last popularity poll as fifth most popular female character in the series, and is also the most popular character from the Thriller Bark arc surpassing even Kuma. Her popularity has grown so much she is now playable in some of the new One Piece games, where most playable characters are either main villains, the Straw Hats, the Warlords or important Marines.
The reason that Portgas D. Ace got more screentime in the anime than in the manga (in the manga he never traveled with the Straw Hats) was that he became so popular with the fans, even though he only appeared in a grand total of about two-three chapters.
Pandaman started out as an Easter Egg-type character that would just show up in the background, and was so popular with the fans that he ended up with his own pirate crew and bounty.
The most recent polls have shown that Kaku has reached this status, being the most popular character outside of the crew and Ace (9th overall). It is difficult to explain why without ruining some very wonderful surprises in the Enies Lobby arc, so let's just say he's a particularly good example of The Comically Serious and leave it at that.
The popularity polls have also placed Dracule Mihawk as high as eighth when he hasn't done a whole lot since the Baratie arc.
And he just showed up to fight Luffy. And it was awesome.
Cool Old Guy Silvers Rayleigh, who appeared for a grand total of three chapters and had a fight which lasted about twenty seconds in the arc he was introduced in, yet is overly popular.
Trafalgar Law, who appeared in the same arc as the aforementioned Rayleigh and got even less screentime until recently, ranked above Usopp, Franky, and Brook in terms of popularity in Japan, and is quite popular in the West as well.
Crocodile is quite possibly the most popular villain in the series, which may or may not have had something to do with his recent return to the main story. As an ally of all things.
There's also Mr. 2 Bon Kurei, or Bentham, whose hilarious mannerisms and gigantic heart have earned him the admiration of more or less the entire fanbase.
Crazy Awesome Emporio Ivankov is also quite popular among some fans.
Vice Admiral Johnathan might count to some degree. He only appeared in a rather good filler side story (the G8 arc) but can be seen assembling at Marineford in preparation for the Whitebeard Pirates war along with his two subordinates.
The Fishman Island arc got a somewhat mixed reception by at least its Western audience, and so did most characters of the arc. However, ask basically any fan, and he will admit that he loves Zeo, who is a member of the arc's Quirky Miniboss Squad and a really good example of a Comically Serious character with hilarious I Meant to Do That tendencies.
A unique Love to Hate example similar to Crocodile, would be Akainu, previously a one note vice admiral who had a notable action of exterminating a civilian ship with the possibility of there being a scholar on there, as well as the admiral with the least screen time. Cue the Marineford arc, his overall Badassness, Determinator tendencies, control over the power of the magma Devil Fruit and his choice of words that led to Ace's death, breaking the long standing rule of "No one important dies outside of flashbacks" has caused him to become one of the top enemies Luffy wants to defeat and notable villains in the series just based on his overall role in the arc.
Badou in DOGS, in the original graphic novel before the manga was picked up for serialization, was a one-off character in a gag side-story who became so popular that by the time the manga was serialized, he was added to the main cast and even given a Day In the Spotlight issue. To a lesser extent, Enfants Terribles twins Luki and Noki were also like this, again introduced in a one-off side-story but eventually added to the regular story as semi-recurring villains due to their popularity.
Fushigi Yuugi character popularity polls usually result in Nuriko, Tasuki and Chichiri taking the top three spots (in varying order), often winning handily over Miaka and/or Tamahome.
Undertaker was probably never supposed to be as popular as he is. His voice in the anime might have something to do with it.
Also: Grell Sutcliff in hernote Grell is Male-to-female Transgender according to Word of God shinigami form, hoo boy. She had maybe a chapter in the manga, and she got so popular that she became a recurring character in the anime.
There's an in-universe example in one of the OVA. Some children are bored when they watch the play Hamlet but they all love a character in particular, a seaweed played by Ran Mao.
Roberta from Black Lagoon easily qualifies. It's not hard to see why as the moment she shows up in Roanapur the body count skyrockets. This in a town where murder is only a crime if you haven't paid off the police chief or are interrupting his golf game.
Sawyer The Cleaner is a goth body disposal expert with a throat scar, voice synthesizer and a huge freaking chainsaw. She only appears in one arc in the anime but it's pretty obvious why she's become so popular with the fans.
Desler/Desslok from Space Battleship Yamato was an Ensemble Darkhorse because he was so good at being bad. And because he was quite a Woobie when his planet was destroyed by the Star Force.
Slayers: Among the less-major characters, Sylphiel's replacement in the third season of the anime, Filia, has become extremely popular because of her status as an adorable, headstrong, and mighty Golden Dragon with a lovely human form. Her being paired with Xellos is more or less one of the most popular pairings of the franchise.
Xellos himself is also well-loved: an allmighty demon who loves to tease and is probably the biggest mastermind of any character, even moreso than some of the gods and demons that are stronger than he is.
Bobobo bo bobobo: Pickles, a designated Butt Monkey one-off character, won a "which character would you like to see again" popularity poll in Japan, and was thus given an integral role in the final arc of the series.
Jelly Jiggler was originally going to be a one-off character (similar to Pickles), but fans clamored for him to appear more during the early days of the manga. Yoshio Sawai then made him a part of the main cast.
Rice is extremely popular in the western fandom, despite only fighting two major battles in the entire series.
Higurashi's Big Bird, Kuwabara Biker, Hitler Stache, and Swastika Biker all became ensemble darkhorses in some circles after their appearances.
Angel Sanctuary has in a cast of dozens (or even hundreds) at the very least one character who didn't live to the end (damn, he didn't live through the first arc) but when he was finally killed got a whole chapter dedicated to him and his awesomeness (even the side bar was all about how Kaori felt for him to die and the fans were worried about what would become of him afterwards so it was included in the last chapter's epilogue). Meh, talking about Katou Yue here, of course.
As soon as Kate appeared in Sketchbook ~full color'S~, she immediately pushed the other characters off stage—including Sora, the original protagonist. In the manga her role soon got relegated to word jokes, but her introduction halfway through the anime made sure that she is likely the most-recognized character from that series.
Token Mini-Moe Yuki from Saki managed to gather quite a fanbase, even though she acts primarily as a comic sidekick.
Momoko also has got her share of followers later in the series, perhaps due to her interaction with Yumi. Heck, she's popular enough to become the cover girl for Vol. 5, even though she only appears briefly there and has had very limited screentime beforehand. She only started appearing during the second half of the second to last match of the finals, literally.
Hisa is also quite popular because of her competency and generally cool demeanor.
To Love-Ru: Yui is far and away the most popular girl in the cast. Momo also has a rather large fanbase in proportion to her screentime (which isn't that much), but nowhere near as much as Yui. Not surprising, since tsundere characters are usually always popular and Yui is pretty much a textbook example of a Type A tsundere.
In Sasameki Koto, Kiyori's dry humor garnered her a significant fanbase, which got propelled by the way she is presented in the anime. This is an impressive feat for a straight female character in a yuri series, although her cute, laconic laugh ("ha-ha-HAAA") may have a lot do do with this.
Despite receiving less attention as time goes on, Miranda's popularity has increased with each successive popularity poll, and by the fourth one she reached fifth, surpassing the consistently popular Krory.
Kaworu Nagisa from Neon Genesis Evangelion. He only appeared in one episode, with about fifteen minutes of screen time - counting all the freeze frames -, but being his optimistic, charming self, he managed to become one of the show's most popular characters - As it would seem, even the Creators (who originaly had intended him to be unsettling) got to like him, as the various adaptations and remakes of the anime have elevated him to one of the central characters, though his alliegiances vary.
While not as popular as the above two, Maya Ibuki has a dedicated following which her small role would not attest to - her two fellow technicians, Makoto Hyuga and Shigeru Aoba, aren't nearly as well-liked. The fact that she's not nearly as screwed up as some the main characters probably helps.
Just like Taniguchi and Misao, Hideyoshi also got his own solo Image Song after the series. All three series were produced under Lantis, so this may be the case for any future Ensemble Darkhorses from a series they sponsor.
Eri and Yakumo's love triangle with Harima have caused them to eclipse Tenma as School Rumble's most popular female characters.
Kinnikuman has done this more than once, with characters introduced by the creators as one-off villains taken from fan submissions who end up becoming popular enough that they gain expanded roles later on. Examples include Ramenman, who ultimately got his own spin-off anime, and Buffaloman, who got himself promoted to leader of the Seven Devil Choujin over Black Hole because the creators recognized this trope in action.
TK is a one-dimensional side-character with almost no dialog, but in a popularity poll shortly after the start of the series he was one of the only two characters (the other being the Moe antagonist) who got hundreds of thousands of votes, while the main viewpoint characters got just a few hundred. Of course, what with speaking almost entirely in silly Gratuitous EnglishCatchPhrases and acting like a cross between an action hero and Michael Jackson, he may be an intentional example.
Though not so much as TK, Shiina seems very popular as well. Her Aloof Dark-Haired Girl qualities along with her obsession with cute things seemed to have earned her a lot of points with the fans.
Aoki from Hajime No Ippo. He's a massive buttmonkey, but that doesn't stop him from continually ranking high on popularity polls.
Nurarihyon No Mago had a few surprises in the first popularity poll, namely when side character Tsurara Oikawa the Yuki-Onna wound up only eight votes behind second place, leaving the designated love interest far behind her Body Guard Crush.
Casshern Sins has Sophita, a one shot character who shows up on a surprising percentage of fanart.
Most of the cast of Magic Kaito are dark horses when they appear in Detective Conan, most notably the Kaitou Kid himself, who some fans like even more than the main character, Shinichi.
The Kaitou Kid's rival, Hakuba Saguru, despite being something of an ensemble Dark Horse within Magic Kaito itself, still has a rather large fan following among Detective Conan fans, despite having only appeared in two DC story arcs and sort-of one movie.
The officers Satou and Takagi are also big fan-favorites.
Matsuda Jinpei, Satou's ex-half-boyfriend, appeared only in flashbacks for about three episodes, having died years before the events of the manga began, yet he got his own keyhole appearance on the back cover and is sometimes considered one of the (admittedly numerous) main characters.
In Muhyo And Roji, Panza only appears in Volume 6 and dies at the end of the volume, but ranks sixth in the popularity poll.
In Bakuman。, Hiramaru, a side character who does not interact with or impact the main characters much, reached third in the popularity polls, past Takagi and Azuki, while Eiji Nizuma took first place, also surpassing Mashiro.
Sirica, the daughter of the legendary Galaxy Soldier Garlude, who appeared in Episode 60. Many fans came to love her so much that a lot of fan art of her can be found all over the internet. Sirica herself was so popular that she even later appeared in the final two episodes alongside Knuckle Joe, Sir Arthur and his three knights (Sir Falspar, Sir Nonsurat, and Sir Dragato).
Garlude and Knuckle Joe's Father also got the same treatment as Sirica herself. And even the rest of the Star Warriors and Galaxy Soldiers, and even the traitor Yamikage.
Chilidog/Wolfwrath is also quite popular, as a lot of fan art for it can be found across the internet as well. Some people would even draw a scarier version or a cuter version, or even a baby Wolfwrath puppy.
Eyeshield 21 has Rui Habashira of the Zokugaku Chameleons, a slimy delinquent who proved ridiculously popular with the show's fandom despite being at best a minor supporting character. Fans' prayers were answered when he was revealed to be the mystery player on the World Cup team. In an even more baffling example, Gokuu of the Shinryuuji Nagas is an extremely minor character who has a decent-sized fanbase (well, in Japan).
All of its antagonists are Ensemble Darkhorses, to a degree, because of how badass and/or sympathetic they are: Sayoko, Mara, and Hild. Unfortunately, Hild has more or less displaced the other two as of late.
Mami is only seen for a few episodes before getting Killed Off for Real (she does make appearances after that in two episodes), but due to her sheer badassery and really awesome theme, she is well liked by the fans.
Kyubey's face shows up in the strangest of places in Japan - namely arcades and price tags for stuff in specialty stores -, not quite rivaling Tony Tony Chopper's popularity in that respect but getting there. A curious case considering he is the closest thing to the series' main villain.
The witch Charlotte is seen for all of two minutes and is also quite popular. Probably because she's adorable. And there's not really anyone else to ship Mami with. It's probably no coincidence that when the official Madoka Magica video game was announced, Charlotte was the first witch to appear in the preview images. Like Kyubey, she's a strange example since she devours Mami alive yet much of the fanart revolves around her cute, innocent appearance.
Future GPX Cyber Formula: Bleed Kaga, who despite making a few appearences in the first half of the TV series, is so popular with Japanese fans that he becomes a regular in the series, has number of CDs about him and he eventually is made into the main character in SIN, the final OVA.
Jonathan Wolff in the Robotech series. He made one memorable appearance in the New Generation (Mospeada) segment where a big deal was made of him being a legendary hero. Then he was spun off into the aborted prequel Sentinels and a large number of comics and stories, all despite the fact that (in that Robotech episode, he is shown to have sold out to the enemy and almost gets Scott Bernard killed)
The North Maiden from Star Driver became very popular with parts of the fandom, even though she only appeared for 8 episodes. So much that it surprised the creators.
Keith Goodman a.k.a. Sky High from Tiger & Bunny. Biglobe ISP conducted a character popularity survey of most of the shows from the spring 2011 anime season. Behind the title duo (Kotetsu T. Kaburagi and Barnaby Brooks Jr.), Sky High was the most popular character in the series...And the entire season.
In Go Lion, the black-shirted, original Blue Lion pilot, Takahashi Shirogane, was intended to be nothing more than a Sacrificial Lamb, Killed Off for Real in the 6th episode. But he proved to be enough of an Ensemble Darkhorse in Japan, that Toei studio tried to bring him back more or less, through the awkward method of creating a Backup Twin who showed up later to avenge his brother. When World Events Productions adapted Go Lion into Voltron, in an inspired stroke of Woolseyism, the 2 bothers were combined into one character, Sven, who was severely injured in that 6th episode, but later recovered. As Volton's popularity skyrocketed around the world, so did Sven's, a Badass Normal with more impressive credentials than either of of Go Lion's 2 brothers could've had individually.
Makoto of AKB0048. She easily has the least amount of screentime of the main understudies, alongside Linda, yet she still manages to rank 3rd on the official popularity poll, behind the two mains. She's very popular among the western fanbase, as well.
One may not believe this, but Rose of Versailles started as a biography of Marie Antoinette with her as main character, but a certain Oscar Francois de Jerjayes outpaced her in popularity and stole the main status from her.
Shiro Sanada (Sandor in Star Blazers) was unusually popular. Unusual because although he wasn't as old as Okita or Tokugawa, he was still considerably older than Kodai, Shima, Yuki, and the other young characters. This usually means that he would be in line to get killed off (along with the other older characters) so that the story can focus on the younger characters development. This did not happen and he went on to become, after Kodai, the most longeval character in the Yamato Saga. In the most recent installment, Space Battleship Yamato:Ressurection, Sanada (now head of the EDF) now outranks his old captain, Kodai
Saburo Kato (Conroy in Star Blazers) was also unexpectedly popular that the producers regretted killing him off in the Yamato II series. They made up for it by introducing his younger brother Shiro Kato in the next installment. Star Blazers viewers won't notice the difference, however.
Girls und Panzer has Saki (maybe better known as "autism-chan"), a popular joke character with no lines (save one occasion in Episode 12) who's often seen staring off in weird directions. Many explanations have been given for this, from looking into alternative timelines/dimensions, to being a tank tracking device, to being aware of the 4th wall and looking at the viewers.
There's also Jagdpanther-chan, an nameless commander of a Jagdpanther in the finals, who gets detracked more than once and desperately races to repair her tank.
The Occult Research Club President of Mahoraba, despite being a rather minor character compared to everyone living in Narutakisou, took third place in a character popularity contest. Or depending on your view, second place, since first and second is Kozue, due to her multiple personalities.
Thanks to the So Bad, It's Good, meme-spawning nature of the show, Chargeman Ken has many of these. The most notable case would be Hoshi - he only appeared in the 4th out of 63 episodes, and still has more fanart and time in MADs (Japanese YTPMVs) than the main character.
Of the official members of the Ham-Ham Clubhouse, Panda and Cappy have appeared the least often in the series, making them considerate dark horses.
Jingle, the wandering ham poet.
Oxnard's girlfriend, Pepper, stands out quite a bit.
Ask any Date A Live fan which character would they like to see more of and chances are that their answer is Kurumi. How good is she? She's literally the difference between a bottom tier Twelve Episode Anime and a top tier one. People hated the first 6 episodes but loved the next 3 episodes for a reason.
And from episodes 9-10 we have Efreet!Kotori to keep the momentum going.
By extension, his squadmates have gotten a lot of respect from fans, Petra especially. They all end up being killed off, however.
Bertolt is pretty popular for someone with not many lines and notably less screentime than the other trainees. Especially on certain imageboards, where he is hailed as some sort of moeMemeticWoobie due to his sweating and his awkward and distressed facial expressions. And then it turns out he's the Colossal Titan that kickstarted the plot and thus one of the most relevant characters
Exaggerated and Played for Laughs with the so-called "Kawaii Titan◊". People keep making it out to be a marvellous, beautiful, innocent creature that had it's life horribly cut short by Mikasa in the Warehouse battle, despite the fact that it was responsible for killing Mina Carolina and came scarily close to killing Sasha as well.
Speaking of, Mina as well. She's a simple Mauve Shirt with only about a page's worth of dialogue before she's munched by the Kawaii Titan during the squad's ill-fated First Battle of Trost, but she's got a surprising amount of attention from the fandom.
Hanje, Levi's Lancer, is extremely popular among Western fans for being crazy.
Marco gained a lot of respect after his death at the hands in Trost.
Hiei was originally supposed to be nothing more than Yu Yu Hakusho'sStarter Villain, but fans kept asking when they were going to see him again, so when Kurama was brought in to become part of the team, Hiei came with him.
The villain Wolfrun has gained a surprising amount of popularity, almost to Draco in Leather Pants level. One day after the first episode of Smile Pretty Cure, Japanese art site, pixiv, displayed about 5 pages of fan art of him, a lot of it even pairing him with Miyuki.
Joker isn't immune from this either, particularly at Tumblr.
After episode 23, Majorina in her more powerful AND sexy form is also getting this treatment, with quite a handful of Pixiv fanarts just hours after the episode aired.
Ikuyo Hoshizora probably has more fanart on pixiv than any other Precure mother in the entire franchise.
Hime Shirayuki/Cure Princess, especially with the Westerners, due to her brattiness not being annoying or over-the-top, as well as having the best, most well executed character development out of all the characters.
The International Cures such as the American team, the Bomber Girl Pretty Cure, has plenty of artwork despite only being seen for, like, ten minutes tops. In fact, on the Pretty Cure Wiki, there was a poll to choose your favorite international team, and guess what? Bomber Girls beat them all by a land slide.