Jayne: Captain, can you stop her from bein' cheerful, please? Mal: I don't believe there is a power in the 'verse that can stop Kaylee from being cheerful. Sometimes you just wanna duct tape her mouth and dump her in the hold for a month. Kaylee: (Kissing him) I love my captain.
The Cutie is a character who is known for being sweet and lovable, more comic relief than anything, who likes nothing more than to pet little puppies. They make you adore them, root for them and love them.
They are known for being very idealistic, cute and innocent. Some of them even may act in a childlike manner to emphasize their innocence with an upbeat and positive attitude. They also tend to be genuinely nice, loving, caring, and kind to whoever is with them. They tend to take the most peaceful solution to a conflict and hardly ever (if ever) harm others in any way. They're most often female, though younger boys can also be this.
Their innocence and purity draws the sympathy of the audience for them. For this reason they tend to become The Woobie when bad things happen to them.
Related to Break the Cutie, Kill the Cutie, The Fake Cutie, Corrupt the Cutie, Moe, The Pollyanna, and All-Loving Hero.
Madoka Kaname is so adorable that Sayaka jokingly(?) declared that she couldn't let her become popular with boys.
Homura was originally an Adorkable version of this in the original timeline; glasses, pigtails, kind yet unsure of herself, etc.
Chi from Chobits is one of the cutest animé characters ever made. Not only is she absolutely gorgeous, she is unbelievably innocent and sweet. Add the fact that she has the mind of an innocent baby (she's a persocom whose memories were erased and so she has to relearn everything)'', and her saying "Chi?" at least eight times per episode and you have a serious overdose of cuteness in one lovable character.
Tomoyo of Cardcaptor Sakura, despite her notable fondness for Sakura, is near infallibly charming and innocent. Sakura herself leans more and more into this as the series goes on (especially if Syaoran is involved).
Betty Cooper from Archie Comics, a competitor for Archie's affections. Betty often takes time for caring about others especially nurturing Archie. In an episode, she had to excuse herself as she was tutoring elementary students at the local library. Veronica discovers this as spies on her thinking Archie was cheating on her.
The Pollyanna, an archetype which is used to describe irrepressibly cheerful characters. She lives in a town of bitter and angry people and slowly makes them cheery.
Despicable Me has Margo, Edith, and Agnes, the most innocent of Gru's adopted daughters.
Every now and then the women of the James Bond franchise fall into this. The best example is Ms. Caruso, the Innocent Fanservice Girl of Italian origin, caught in bed with Bond in the opening of Live And Let Die.
Live Action TV
Firefly: Kaylee is by far the most cheerful character on Serenity's crew which is why she provides the page quote.
Murdoch Mysteries: Anna Fulford is a very sweet and very kind young English woman and Detective Murdoch's Temporary Love Interest. Even Julia, who should be jealous of her, says that Anna's lovely and seems to really mean it.
'Allo 'Allo! has quite an unlikely Cutie, because Lieutenant Gruber is a Wehrmacht officer in the occupied France. Yet he's sweet, well-mannered, polite, civil, enthusiastic, a great pianist and has a crush on René, which is unfortunately a case of Incompatible Orientation. He keeps apologizing whenever he's forced to search people or carry out orders he's uncomfortable with. He likes his "little tank" and only he can make "Heil Hitler!" sound adorable.
Cat Valentine from Victorious and now Sam & Cat is cuteness in human form. Just try not to go "Awwww" one or twenty times an episode on seeing her. You can't, can you?
Duel Savior Destiny: Nanashi is the cutest/cutesiest and most innocent character in the story. She frequently uses the third person and has her own verbal tic. She's very hands on and affectionate. She's also undead, so the main character wants nothing to do with her or her affections.
Fallout 3:Moira Brown, Megaton's shopkeeper and tinkerer in science . She sticks out for being perpetually cheery and upbeat in a blasted post-apocalyptic wasteland.
Rinoa from Final Fantasy VIII. Reportedly, Tetsuya Nomura, the head character designer for Square at the time, specifically wanted her to give off a "cute" vibe, and built her character around this idea.
Final Fantasy IX: Vivi, the adorable little black mage was so loved by fans, he made a cameo in Kingdom Hearts 2. Throughout the game he acts like Zidane's kid brother and fidgets with his hat when nervous.
Film Conscience: Ringo represent the more cheerful, optimistic side of Luke.
The Lizzie Bennet Diaries : Jane Bennet is universally loved and admired. She's adorable and nice to everybody, and genuine in her sweetness. Interesting how a woman in her mid twenties can pull this off.
Clover of the Whateley Universe. One of the youngest kids at Superhero School Whateley Academy, she's a naive wizardess-wannabe with the cutest puppy ever. And a witch hat she's sure will give her magic powers. She also happens to be a powerful Reality Warper and her puppy Buttons can turn into a monstrous dog the size of a pony.
Surprisingly it has this in Cassy, an animate drawing of a sweet and friendly young woman who everyone at the Foundation adores. Unfortunately she found out about her two-dimensional condition and has been in depression ever since.
There's also SCP-054 a friendly entity made of water that likes to play with personnel. Unfortunately frequent experimentation on her (mostly by men) has caused her to resent men and be fearful of them.
Miss Martian in Young Justice invokes this trope. Though genuinely kind, her mannerism and appearence was constructed from a short-lived cheesy sitcom called "Hello Megan", and her true form is a horrific monster. She almost betrayed her friends to keep the truth hidden, and in the second season develops a very dark tendency for Mind Rape.
South Park: In the season 1 character commercials, Stan was labeled as "The cute one".