"Genki" is Japanese for energetic or enthusiastic. The Genki Girl is a character — usually a schoolgirl, but not always — who acts like she's been mainlining Red Bull and crystal meth. She is possessed of an over-abundance of energy, such that she runs everywhere (often with arms waving wildly or outstretched like airplane wings), speaks quickly (sometimes unintelligibly so), and always does everything fast, fast, fast! She's filled with confidence and determination, regardless of whether she's competent or not. Although usually played exclusively for comedy, sometimes the Genki Girl slows down for a serious or introspective moment. But not for long — she lives her life full-throttle. To sum it up, a good way of telling whether a female character is genki or not is to see if her family and peers are exhausted, astonished or even creeped out by her chronic outbursts of vitality. (A female character is by far the more common version, but this trope is not limited to females)
Despite what you'd think, the Genki Girl is usually not The Ditz. However, there have been a few blends. She is, of course, very often a Motor Mouth or a Nicknamer. If she focuses her powers on getting a boring guy to relish life, she's a Manic Pixie Dream Girl. Less sympathetic portrayals often make her the Jerkass of the group. Alternatively she could be both. Some are even the resident Cloud Cuckoolander.
If this is a RPG setting, she's almost always going to be the Fragile Speedster, thus fitting her personality. If she is in a Five-Man Band, she will almost certainly be The Big Guy (and probably an exception to the above if she is).
If a work of fiction gives its characters symbolic flowers that represent their personalities, the Genki Girl will likely get the sunflower while her animal is the cat, though her energy won't necessarily make her go crazy.
Whatever you do, don't give them too much coffee, cola or sugar. And definitely teach them that hard drugs are VERY, VERY bad. This is why she may be preferred with somebody who is practical.
Voice actors sometimes become famous for just being able to keep up the role.
Compare Fist Of Enthusiasm and Hot Blooded. Compare The Pollyanna for endless optimism and cheer rather than energy.
Keet is a related but separate trope.
Contrast Emotionless Girl.
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Female examples:
Anime and Manga
Kurata Sana from Kodomo no Omocha is the archetypical Genki Girl. The Fan VidCaffeine Ecomium gives some inkling of just how energetic she is; none of the sequences in this video have been sped up.
Excel Saga's director also gave us Poemi from Puni Puni Poemi. Impossible as it may sound, at times she surpasses even Excel in genki-ness. Puni Puni Poemi seemed to be a deliberate attempt to cram all the insanity of its parent series into two episodes.
The title character is a very avalanche of Genki Girlness, who drags everyone nearby along with her. This is expressly stated in the audio drama's main song "First Goodbye", which is, in-canon, written by Haruhi herself (and just as autobiographical as "Lost my Music") with the line "Igai to genki!".
Tsuruya-san, a minor character, is somewhat of a Motor Mouth and a cheerful Genki Girl, with emphasis on the 'cheerful'. A natural co-conspirator with Haruhi. (When Haruhi isn't working with Little Sister.)
In the 9th/10th novel introduced Yasumi absolutely qualifies. No surprise, considering her true identity: Haruhi's subconsciousness.
Self-described "wildcat high school girl" Tomo (pictured above), when she isn't being a Jerkass and a Ted Baxter. We know she's a Genki Girl because "Genki!" is the first thing she says.
Yukari-sensei is what happens when the Genki Girl grows up. Or doesn't.
Huang Bu-ling from Tokyo Mew Mew, whose sprinting and flailing is often accompanied by circus tricks like running on top of a ball or breathing fire. As Mew Pudding, most of her fight scenes consist of jumping around and climbing things.
Mikoto from Mai-HiME subverts this trope nicely by simultaneously being a Dark Magical Girl. (Push this type of subversion even further, and you wind up with the Perky Goth.)
Several characters in Mahou Sensei Negima! count; Makie is the most notable example. The entirety of Mahora Academy is described as such, even the boys, by the teachers themselves. It was stated that during a previous School Festival, they arranged an academy-wide game of tag, and afterwards decided not to do that again because there were too many injuries. That year, they were going for a (slightly) more sedate game of Hide-N-Seek, until the Big Bad of that arc provided an army of robots, and they decided to unleash the students on them instead.
Winry Rockbell of all incarnations of the Fullmetal Alchemist series. She goes full-on Bishie Sparkle, Squee, and arm-wavy mode whenever she sees something cute or acting cute (Elysia Hughes weeded this mode out of her the first few minutes after she met her), something's caught her interest (mainly anything involving automail, i.e. Rush Valley, or a shopping spree in Central), or a rather vicious (and comic) argument with Ed (again, mainly over automail). The times that she's not Genki mode are when she's realized something tragic or an error in her construction ( i.e.: learning about Maes' death or discovering the missing screw in Ed's newly constructed automail arm after he left to go investigate Laboratory #5), or when she's concentrating on building a new automail body part.
Haruna from Kokou Debut (also titled High School Debut) is so genki she's almost Badass Normal. One of her recurring sentences is "let's work hard!" — cue to high-fiving everyone, running around doing more physical work than the guys and tiring everyone out. Oh yeah, and she can put up a physical fight with guys including potential assaulters. Her over-the-top genki-ness is arguably part of what makes her such an endearing character.
The first Girlfriend of SteelGaiden Game keeps her in character. The set-in-episode-26's-alternate-universe sequel, however, plays this trope straight.
She gets the same treatment in the alternate universe manga Angelic Days (also based on episode 26's AU). So... weird.
Torako from Hyakko. She's of the Genki-Ditz blend, considering she makes her debut by leaping out of a window. It's a second story window, but she definitely chooses the quickest way to get from point A to point B.
Kaguya Sumeragi is like this, as well as The Ojou. She also proves herself to be smarter than you'd guess, becoming the head chairman of the UFN council.
Shirley and Euphie, the respective Love Interests of Lelouch and Suzaku, are also these, and give some much needed lightness to their troubled lives. Unfortunately, and ironically enough, things do not well end for either of them, and both of their heartbroken counterparts descend further into darkness.
Ahiru from Princess Tutu — who is a duck that can magically turn into a girl — spends most of the show running at top speed, squawking out words so fast it's hard to keep up. She's not even aware that her energy level is unusually high, judging by her confused reaction when another girl from her school fails to keep up with her. This may be because her friends Pique and Lilie are about as energetic as she is, or it may be because she's a duck and doesn't know any better.
Sora from Kaleido Star is amazingly energetic. Emphasis on amazingly. Her friends Rosetta Passel and Marion Begnini try to keep up with her, but they still have a way to go.
Hikari from Lamune. Noted by the male lead (her cousin) that she acts much like a kid, despite being a year older than him.
Miria Harvent from Baccano!, who even comes with the equally hyperactive boyfriend and partner in crime, Isaac Dian. They seem to have an amplifying effect on each other (at least their seiyuu have this chemistry.) Since they're inseparable for their entire screen time, it's impossible to tell how Genki they are individually.
Mihoshi Akeno from Sora No Manimani, who's full of energy and passion about two things: astronomy and Saku. She also has a tendency to hug him without warning.
Yuki from Saki, though it's actually a bit of a problem for her Mahjong playing since she loses focus after the initial rounds causing her game to drop.
Natsumi from Taiho Shichauzo (aka "You're Under Arrest") is genki and loud most of the time.
Nina from Tona Gura is so annoyingly Genki, she nearly causes Emotionless Girl Marie Kagura to punish her, something she never does to anyone outside of her brother Yuuji. In his Chivalrous Pervert mode, Yuuji asks that he be punished in her place. If Marie were to choose this option with Tojo Haya, like as not no one would stop her.
Mana, the Egyptian past life of the Dark Magician Girl from the fifth season of Yu-Gi-Oh!.
Bunny from Alice in Sexland pours energy and passion in everything she does. And I do mean everything. That said, she's pretty chaste compared to everyone else in the series.
The titular Cute Ghost Girl from My Lovely Ghost Kana is a strange example. In the back story, she gruesomely took her own life, stabbing herself in the chest many times, and her ghost remained behind, trapped in the apartment building where she died. By the time the real story begins many years later, Kana has forgotten most details of her life, including why she decided to end it. When Unlucky Everydude Daikichi (unable to afford to live anywhere better) moves into the allegedly haunted building, he has a hard time accepting that this cheerful, energetic girl (overjoyed at finally having some company) is actually a ghost.
Usagi Tsukino of Sailor Moon is an obvious example. Eternally cheerful and loud. Her monologue from the Stars season perfectly expresses it. Here's just the end:
Oh, it's almost 7 o'clock on Saturday! Dinner time!
All right!!
With mom's food, and the TV on, my cheerfulness goes up a hundred times! The peace of school, and the peace of my family, and the peace of my sweetheart, and the peace of the universe, I will protect them all together!
Time to eat!
Yes! Energy level at two hundred percent! Cheer bursting at ten billion horsepower! Transform!
Pokémon has a bunch, human and Pokémon alike, though Best Wishes character Iris takes it further (she's this way in the games too).
Bianca, your female rival from Black and White is even worse.
Miyako in Hidamari Sketch. While she's prone to sleep in class and can sometimes sleep for 12 hours in one go, once she is awake, she's quite energetic. One episode shows her coming into Yuno's apartment, showing no signs of having awakened two minutes ago; another has Yuno pointing out that she's hyper even in the morning. "That was quick!" is a common phrase applied to her actions, whether she's gobbling down food or making art (usually impromptu). But despite all her teasing, she's a likable person, a good friend... and surprisingly, does well in school!
Ran Kotobuki from Super Gals, she runs everywhere and shouts all the time.
Ayumi from The World God Only Knows. The first time we see her, she sprinted into the main character, sped through the conversation, and ran off. Into a wall.
Road Kamelot from D. Gray-Man is a particularly creepy version.
Akiko from Eve No Jikan acts like this when the main characters first meet her. They automatically assumed she was human, only to discover that in public, she is an emotionlessrobot girl. This is a facade, though, so being a genki girl really is her natural personality.
Hachi from Nana is called a puppy by her roommate for her energy and desire to please.
Chizuru Sarashina from Wandering Son is a wacky and eccentric girl who does what she wants to, even going against her schools clothing rules (she wore a bikini instead of the school swimsuit once, sometimes wears a tie instead of a ribbon, and wears the boy's uniform occasionally).
Villain Mojo has a Deadpan Snarker assistant, Majordomo, who in turn has a Genki Girl assistant, Minordomo. Minor can be expected to say "Ohmygosh, OHmygolly..." at least twice per appearance, and will get worked up over something (complete with arm-waving and rapidfire talking — her version of it goes from sentences to short phrases strung together in the end) more and more until finally having a heart attack. Luckily, she's an artificial human, so Majordomo just has to hit her reset button to get her up and genki again.
Early appearances of Kitty Pryde started her out as a Genki Girl, though she actually matured during her run with the team.
Her best friend Illyana Rasputin tended towards this when she was in an honestly good mood, which it must be admitted was not all that often after her... growing pains.
Young Ellie from Disney/Pixar's Up! is definitely one of these. Her wonderful mania for living makes you feel for her all the more when she finds that she can't have children.
Jessie from Toy Story 2 and 3. What we see of her Show Within a Show character is pure Genki; in her real-life personality, though she displays quite a bit of cynicism and remorse, she still manages to fit this trope.
Trixie the Triceratops from 3. Bonnie from the same film seems like she'll grow into one of these as well.
Dory from Finding Nemo. Ellen Degeneres, her VA, is a real-life example.
Rapunzel from Tangled is pretty lively. Her never having been outside before only makes her more excitable.
The Little Mermaid has Ariel who frustrates her father with how energetic and adventurous she is. Years later when she's grown out of it she ironically describes herself as "a real fish out of water".
Jordan: I never sleep, I don't know why. I had a roommate and I drove her nuts, I mean really nuts, they had to take her away in an ambulance and everything. But she's okay now, but she had to transfer to an easier school, but I don't know if that had anything to do with being my fault. But listen, if you ever need to talk or you need help studying just let me know, 'cause I'm just a couple doors down from you guys and I never sleep, okay?
Every role Bollywood actress Genelia D'Souza has done. Ever. Even in the non-Bollywood Indian movies. Her most famous Genki Girl role was in the Telugu film "Bommarillu". It was remade into three different languages, and she played the same character in ALL OF THEM.
Christine McIntyre's character in The Brideless Groom. She doesn't even have a name, but she leaves one heck of an impression.
Sophie in Mamma Mia!. Donna and her friends are quite energetic as well, despite being in their fifties.
Bahia Ben Mahmoud in the french movie Le Nom des Gens.
Quorra from TRON: Legacy is very much one when not in a life-threatening situation.
Literature
The eponymous character of Anne of Green Gables, who has a tendency to spout monologues lasting for more than a page. She stops this in the later books, though.
The eponymous character of the Junie B. Jones series. So. Much.
One of the first eccentricities Winterbourne notices about Daisy Miller is how she's just overflowing with energy and enthusiasm. "It was many years since he had heard a young girl talk so much."
The eponymous character of the Ramona Quimby series is rambunctious and noisy and described as "the cheerleader type" by her older sister. Her excitable nature has been known to clash with her friend Howie's stoic demeanor.
Andrew Vachss's Burke books have Pepper, although speaking to Burke somehow puts a damper on her energy.
Permanent Rose Casson, and how, from the Casson Family Series. She is described as recklessly boisterous (going so far to cause a traffic jam just to meet a boy her brother knows - and she's only eight!) and when told that her father is going to New York, she about bursts with energetic excitement. Also her older sister Caddy fits to a lesser extent.
Beverly Brook in Rivers of London, her enthusiasm frequently leaves protagonist DC Grant exhausted. Especially when she is near a river (well she is an Anthropomorphic Personification of the river by the same name).
Quite a few of Anne Tyler's heroines qualify, especially Pauline in The Amateur Marriage (one of the many reasons why she and her husband Michael are so mismatched). There's also Maggie in Breathing Lessons, Rebecca in Back When We Were Grown-Ups, Pearl and Jenny in Dinner at the Homesick Restaurant, and Muriel in A Patchwork Planet.
Rachael Ray from her eponymous talk show. She purposely avoids "sob stories" and almost always has a smile on her face. She also works 100-hour weeks and is a rather shrewd businesswoman, and her energy and determination are usually quoted as the source of her success.
Giada De Laurentis is a somewhat more sedate Genki Girl, also on Food Network. What probably helps is that, with that largish head and especially large eyes of hers, she even almost looks like a real-life anime girl. Or, to put it visually....◊
Sandra Lee, once again from Food Network... well, fits the "dosed up on caffeine" requirement at least.
Ingrid Hoffman is relatively sedate on her English-language show, but watch her in Spanish... it's like Rachael Ray raided Giada's closet.
Elliot Reid was for the most part of the first few seasons highly enthusiastic and quick-talking, tempered with bouts of self doubt (audience: AWWWW!). Her enthusiasm was more of a mask. She was very neurotic on the inside, due to bad childhood experience, overbearing parents, etc. She could be considered a Genki Girl later on, the way she pushes her boyfriends about (sometimes literally).
Cherry, particularly in her early appearances. When she first started work at the Mill, Michelle got her to put away all the medicine that had been left out, expecting to have to sort it out herself later. Not only did Cherry get it done in record time, while she was at it, she alphabetized all the cabinets to make things easier to find.
This is a common trait on Coronation Street right from the first episode with Linda Chevski(which aired December 9 1960 ) to today's Kylie Platt. Combine this with Really Gets Around and you get one of the shows favourite archetypes the classic "Tart with a Heart".
Kang Jong Hee in Wild Romance is bipolar, so she goes through periods of excitability and depression. When she's happy, she's exceedingly happy and takes to biting people.
Professional Wrestling
Mickie James, though she fitted the bill more when she was playing her psycho character. Her entrance theme was a Suspiciously Similar Song version of "Hey Mickie" and she would literally bounce all the way to the ring. She calmed the bouncing down after her Heel Face Turn but still fit the trope.
AJ Lee when she was on NXT season 3. Overly perky and energetic and she once appropriately had to give a speech about caffeine. "Caffeine will perk you up but I'm some natural dynamite baby".
Christy Hemme from the first Diva Search was like this, standing out as the only girl who actually had a lot of personality. Trish Stratus even told her with her winnings she could go buy herself some decaf. Christy responded "it's all natural".
Jessica James from the indie circuit and SHIMMER fame is like this as well. It rubbed off on her tag team partner Rachel Summerlynn when they formed Rachel And Jessica's Excellent Tag Team.
Pathfinder's Curse of the Crimson Throne AP gives us allied NPC Laori Vaus, the disturbingly enthusiastic cleric of a god of Pain and Loss ( Hellraiser ). So genki, she creeps out other members of her church.
The book she's introduced in includes the wonderful description of how she made her pilgrimage "Armed only with her indomitable optimism and an appetite for pain."
Rikku in Final Fantasy X. The sad over-tone of Final Fantasy X kept her Genki-ness down a bit (and despite that she's still eccentric and cheerful). In Final Fantasy X 2, Flanderization sets in and she is now Genki Girl incarnate. Although perhaps not to the degree of her 'sisters', Penelo of Final Fantasy XII fills in this spot alongside Vaan in an otherwise very no-nonsense group.
Kula Diamond in all her hyper-cheery, candy-loving, Face Doodling glory. She's especially notable given her status as an Opposite-Sex Clone of the much more serious Kyo Kusanagi, and given that the same experiment that created her led to The Stoic K'.
Yuri Sakazaki becomes one of these later on. She's kinda like that in Art of Fighting 2 and definitely in the Capcom vs. SNK games
Mignon Beart from KOF Maximum Impact. Also, Athena Asamiya, Mai Shiranui, and Metal Slug crossover Fiolina Germi.
Norma Beatty in Tales Of Legendia. She goes as far as giving her party members strange nicknames like Senny and Teach.
Many Suikoden characters are this; sometimes there are many in the same game. For example:
Miakis from Suikoden V... initially. Then she gets saddled with an overload of (mostly justified) angst, but eventually reverts to form over the course of the rest of the game.
An example from earlier in the series would be Nanami of Suikoden II. Her introduction sequence consists entirely of her shaking her brother around out of giddiness for about 2 solid minutes, culminating when she accidentally sends him hurtling into a cliff wall, leaving a hero-sized imprint in SOLID ROCK.
Path of Radiance and Radiant Dawn have Mia, who is obsessed with finding her rival (a swordsperson in white) and dueling people at dawn.
Tiltyu from Genealogy of the Holy War is a tragic example of how a Genki Girl can eventually break down and cannot be Genki anymore for the rest of her life. Sylvia also counts, and for the second half Fee and Patty (and her replacement Daisy) more then fit the bill.
Fire Emblem has Serra (for the most part), Rebecca and Nino, and The Sword of Seals has Thany the pegasus knight and Lalam the dancer.
In The Sacred Stones we have Princess Tana as the typical example and Princess L'Arachel as the trope taken to new extremes.
Aschen from the Super Robot Wars spinoff Endless Frontier becomes this whenever she lets out her full power. Makes for an... interesting contrast with her usual self. She even goes so far as cheerily shouting out things like "ASCHEN PUNCH!" and "ASCHEN KICK!" Considering that, appearance-wise, she looks more like something out of a robotic Amazon Brigade than a Genki Girl, it makes for an amusing contrast.
Izuna from the two merciless games sporting her name certainly qualifies.
Though she gets toned down a bit in the later games due to all the torture and all, Imoen, from Baldur's Gate, is rather specifically described by one character:
Valygar: For someone who supposedly has her soul tainted by the evil of a dead god, you remind me considerably of a chipmunk with a sugar high and a death wish.
Kazooie from Banjo-Kazooie, at least in the first game. In the sequels, she becomes more of a jaded Deadpan Snarker.
Arche from Tales Of Phantasia starts off very much like this, though mellows considerably after the party visits the Elf Village, and her mother is seemingly executed in her place. Which, to be honest, is fairly understandable...
Kaori Nishidake. In a series about death-defying snowboarders, Kaori's excitable nature is explicitly childlike and she just has so much fun out on the snow.
Marisol Diez Delgado from Tricky also qualifies.
The Dryads' voice-set in Warcraft III portrays this kind of personality for the entire race, along with a touch of The Ditz.
"Fall, like leaves! In... fall!"
Neeshka from Neverwinter Nights 2 has elements of this. Note her kleptomania, habituation to speak very rapidly, and general variance between overwhelmingly excited or deeply anxious.
Deconstructed in the GTA Radio from Grand Theft Auto: Vice City, where Amy from the VCPR station is a Genki Girl who was put on heavy anti-depressants ever since her family was brutally murdered.
Gretchen Hasselhoff from Backyard Sports, who is both one of the fastest runners and the fastest talker in the series.
Touhou Project's Cirno is such a genki girl she gets an entire song in which to display it. "Chirumiru, chirumiru genki, chirumiru!" Marisa also displays levels of genkiness. What else would you expect from a Cute Witch that can fire a giant Wave Motion Gun?
Gina of Midnight Club 2 is cheerful, always smiling (or smirking). And Japanese, which explains a lot. (LOL STEREOTYPING)
In a WRPG example, Kasumi Goto from Mass Effect 2 can qualify. She is Japanese too.
Broken for a minute at the end of her loyalty mission with a very effective scene showing her having a quick emotional breakdown. She recovers quickly.
Hagino apparently has this role assigned to her in Canvas 2 and is required to be cheerful or Hiroki will get upset.
In some of the incarnations of Zelda she seems to be full of energy, at least until she gets kidnapped.
In some of the newer games, including Wind Waker and Twilight Princess, she even helps you fight Ganondorf.
Skyward Sword. Apparently, she isn't above dragging her childhood friend around to things she wants to do, doing all the talking whenever she's around (even if Link never talks), and pushing/jumping at him from potentially-lethal flights to make him use the sailcloth/catch her on his Loftwing.
Nelie and Orpha in Eien No Aselia. Nelie's twin Shiah looks like she's trying, but she's a little shy.
Princess Rosella of Daventry - just as fond of adventuring as her dad, impulsive as all get-out, fun-loving and extroverted. Oh, and asked her long-lost brother to prove his identity by showing off a certain birthmark...
The right dialog choices in Persona 3 Portable can turn the female protagonist into one of these, much to the chagrin of the rest of the cast.
Kunoichi in Samurai Warriors. Although she mixes an unhealthy amount of creepiness with it, what with her stalking Yukimura and enthusiastically suggesting the most dreadfully violent solutions to any problems that may pop up.
Ilya is too... except she's a genki not-quite-evil girl who likes dismembering Shirou a bit too much. Shirou also realizes after spending a little time with her that it's all an act and that in reality she's immensely conflicted inside about whether to treat Shirou as a brother or an usurper.
Tsuzuriko/Tojiko in Kara no Shoujo is your stock genki girl... going to school at an academy full of near zombies. You might say she stands out a little.
Sachi in Sharin No Kuni. Natsumi used to be one as well until she was accused of 'seducing' an upper class boy and receiving her obligation. Natsumi gets hers back at the end of Chapter 5 and keeps it in the fandisc
Arcueid Brunestud in Tsukihime... well, when she's not out killing Dead Apostles and is spending time with Shiki instead, anyway. Kohaku definitely qualifies, too. Especially in Kagetsu Tohya and Melty Blood. In the original game, though, this is subverted to point of being a punch in the gut.
Da Capo II has Yuzu, one of the characters in Nanaka's route, who is as genki as they come, despite being an Ill Girl.
From Katawa Shoujo, Emi and Misha, who are rather...interesting variants of the trope. For Emi, while she indeed is a cheery girl, it turns out she's not as drama (or trauma)-free as she initially seems. The loss of her legs was traumatic, but she learned to cope with that well. The loss of her dad she did not cope with at all. Part of getting her happy ending is to help her deal with her loss. In Misha's case, it's partly a pretense to hide the emotional trauma of Shizune rejecting her love confession, as well as being a coping mechanism for said trauma.
Webcomics
Sapphire from Monsterful: The energetic zombie teenager is way faster and louder than a zombie should be.
Grace fits this trope sometimes, though she also enjoys sleeping a lot. Sometimes, she combines the two, resulting in the invention of her legendary "Sleepy Little Ninja Stealth Hug"...
Jade Harley of Homestuck, even her typing quirk is genki - omitting periods and overusing exclamation points and emoticons. Her Troll counterpart, Feferi, also tends to get overexcited about everything.
The hyperactive, lovably eccentric Millie Mudd from Ozy And Millie is a Genki Girl in training.
Larxene in the comic Ansem Retort. She's a homicidal version of this, once nuking Disney World because she couldn't get free Funnel Cake.
"Dear Mr. President: I have solved the world's energy needs. All you need to do is put two girls I know on a treadmill."
Missi from Misfile definitely qualifies. While not exactly hyper, she's drastically energetic and upbeat when compared to the rest of the cast. So far nothing, not even being dumped, has been able to make her sad for more than a single panel.
The always-enthusiastic Molly the Peanut Butter Monster from The Inexplicable Adventures of Bob!. It probably helps that she has a super-fast metabolism and can outrun a bear.
Freddy from Ghastly's Ghastly Comic is about as much of a Genki Girl as they get. (Well, the genki part, anyway. Freddie's as much a girl as she wants to be.)
Fio from Circumstances of the Revenant Braves is a girl of action and gets restless when sitting around for too long. She even hopes for trouble if it will alleviate her boredom.
A comicallyAx Crazy version — Bangladesh DuPree. Her first phrase in the comic is "Ta daa! I am here!" and on the next page she proclaims "Nobody knows more about torture than me!"... just as cheerfully.
Asako from Megatokyo is a Genki Girl of Mass Destruction, and her friend Mami knows the arming codes. As Mami says, "Hey, I always reserve the right to use the "Asako option". You should know that by now."
Skull Girl from Super Temps. She has been barred from coffee and sugar twice, her outbursts can create walls of text, and her energy can demolish a multi-story corporate complex in minutes.
The eponymous (title) character of The Mighty B!!, Bessie Higgenbottom, is an ambitious and optimistic 9 year old Honeybee scout who believes she will become a superhero called The Mighty B if she collects every Honeybee badge.
Uniqua from The Backyardigans is one of those. But in one episode, usually-Tsundere Tasha got to be the Genki Girl and show her deredere side.
Kiina's portrayal in BIONICLE: The Legend Reborn qualify her as one. It's in stark contrast, with how sour she behaved in the novel that takes place before the movie's events — however the movie was written first. It was also the only time we saw this side of hers, but it had already stained her image in the fans' minds.
Starfire from Teen Titans, partly justified in that her powers manifest from unleashing her emotion. (Although all evidence suggests that anger worksbetter in a fight. In the first episode we learn anything about it, she cheerily explains that her starbolts require "righteous wrath".)
Transformers Prime: Miko, who transferred to an America school to escape a life of piano lessons and ends up in the middle of a war between alien robots, to her absolute delight. Also played by Tania Gunadi, who is good at these.
To everyone's surprise, later episodes deconstructed this. Parties are her way of validating herself, and if nopony likes them that must mean nopony likes her.
When your life's career is party catering and cheering everypony up, receiving no approval is the worst that could happen.
From the same series, the Cutie Mark Crusaders are an entire group of these. They tend to egg each other on.
Fluttershy can get like this when animals are involved. Just hearing Rainbow Dash suggest she might want to get a pet is enough to set Fluttershy off.
From the original My Little Pony we have Surprise, whom Pinkie is heavily based off in G4. She enjoys pranking people, is very active, and is very loud.
June from KaBlam! started out as one of these, as well as The Ditz. In season two, she's still this trope at times, but much more snarky. In season three, this starts to drop a little bit more as she becomes a sarcastic Jerkass, and by season four, this is gone and she became a slight example of the only sane girl.
Hayley Williams of Paramore, so, so much, if the way she answers interviews, tweets, and acts on stage is anything to go by. Not many people would Tweet about how much underwear they're going to buy or make jokes about their own chest during an interview.
Felicia Day: Her promotional video for Dragon Age: Redemption is marked by energetic smiling, bobbing, and annotating.
Amanda Tapping, who never seems to slow down and is always bright, bubbly, enthusiastic, and an all-around goofball.
Demi Lovato, when she's in a good mood or with her fans, especially in regards to her fans.
Male examples:
Anime and Manga
Dr. Slump: Asano Keigo is constantly active and cheerful (or entirely down in the dumps), to the point that he gets on Ichigo's nerves. Though Keigo does have some introspective moments, they are few and far between.
Kakeru, the protagonist of Area no Kishi, is a student who channels his love of football into working tirelessly first as manager for his high school football team, and later in the series to overcome obstacles becoming a player himself.
Jackie Gudelhian, Johji Ohtomo and Bleed Kaga from Future GPX Cyber Formula are adult versions of the trope. The latter, however, drops off his genki-ness in the ZERO arc when he began to become serious.
Jeko from the ColSec Trilogy is a small, wiry, hyperactive young man who's always trying to rile the resident Tsundere. (On an off note, although it's not anime, it's mentioned at one point that he's Japanese-American.) Enough said.
Normally, Elliot from El Goonish Shive doesn't qualify for this trope. But he can shapeshift into various female forms, a few of which have their own personalities. There's one called the "Party Girl Form," which is Elliot on a shapeshifting Gender Bender, with a Motor Mouth and Elliot feeling like he just downed a hundred shots of espresso. Appropriately, since this form and personality is so radically different from Elliot's own, this form has been dubbed "Heidi," as it's the closest name to "Hyde.
Western Animation
Aang from Avatar The Last Airbender is—when not having to save the world—cheerfully energetic and quite confident. He provides a contrast to the other guys in his group: snarky Sokka and brooding Zuko.
Odd Della Robbia in Code Lyoko has plenty of energy and confidence. And his Lyoko Warrior form is cat-based.
