Sweetie Belle happily presenting a gem-studded card to Rarity.Sweetie Belle deeply admires her older sister Rarity and tries to show her devotion by helping Rarity with her work and chores. Despite her good intentions, Sweetie Belle's efforts are frequently disastrous, much to the dismay of Rarity. In Stare Master, she tries to retrieve some ribbon for one of Rarity's new outfits, and sets off a chain reaction of destruction that wrecks Rarity's bedroom. In Sisterhooves Social, Sweetie Belle is prepared to spend an entire week with Rarity, but her burning desire to do something nice for her sister creates tension between them. Sweetie Belle starts by burning a breakfast that she was preparing for her family. Rarity cleans the kitchen and cooks another meal, but reluctantly allows her eager sister to garnish a plate with a sprig of parsley. Rarity anxiously guides Sweetie Belle in the deceivingly simple task, but Sweetie Belle loses balance and crashes into the table. Rarity then asks her to take some dirty towels to the laundry room, but in her eagerness to help, Sweetie Belle washes a valuable wool sweater that ends up shrinking in the heat of the sun. To make up for the blunder, Sweetie Belle crafts a card using a crate of sapphires, but Rarity becomes extremely upset because the rare gems were meant for an important client's dress. She refuses Sweetie Belle's offer to help find more gems and instructs her to tidy up the stationery. When Rarity returns, Sweetie Belle says that when she saw the "big mess" in Rarity's work room, she thought she would clean it up for her. However, Rarity calls it "organized chaos" and says that she was just about to finish planning a new fashion line.
Later that day, Sweetie Belle invites Rarity to the Sisterhooves Social competition, but Rarity refuses, calling it "uncouth". Now feeling hurt and betrayed, Sweetie Belle argues that Rarity is ruining her life, and the two have an argument and both agree that they don't need a sister. Sweetie Belle resolutely abandons Rarity, preferring to hang out with Applejack instead. Later, Rarity discovers Sweetie Belle's sapphire-encrusted card and realizes the card had a drawing of the two sisters enclosed in a heart. She tears up, realizing how much she misses Sweetie Belle, and dramatically declares that she will "never be sisterless again". She finds Sweetie Belle camping with Applejack and Apple Bloom, but Sweetie Belle refuses to accept her sister's apologies and storms off.
During the competition, Sweetie Belle thinks she is running the obstacle course alongside Applejack, but it is actually a mud-covered Rarity who had secretly switched places with Applejack at the very beginning of the race. The sisters reconcile and agree that being sisters takes work, but if you compromise and embrace each other's differences, you can have a lot of fun and be close. Rarity confronts Sweetie Belle with Gabby Gums' slanderous articles.In Ponyville Confidential, Sweetie Belle and her fellow Cutie Mark Crusaders become reporters for the Foal Free Press, adopting the pseudonym Gabby Gums. Rarity stumbles upon an issue of the paper and instantly develops a liking for Gabby Gums' writing, unaware that her sister is one of the reporters. Gabby Gums soon begins writing hurtful gossip columns about everyone in Ponyville, an action which draws the attention of Rarity. Rarity soon finds her own diary inside her sister's saddlebag and deduces that Sweetie Belle is Gabby Gums. She confronts Sweetie Belle about the paper, making Sweetie Belle realize how wrong it is to invade someone else's privacy, and how it will make her lose respect from others. After the Crusaders apologize to the public and their siblings, Rarity hugs Sweetie Belle.
In Sleepless in Ponyville, Sweetie Belle invites Rarity to go on a camping trip with Applejack, Apple Bloom, Scootaloo, and Rainbow Dash. At first, Rarity says she despises camping, but Sweetie Belle mentions that Applejack and Apple Bloom are going together, then puts on a pouty puppy-dog face, to which Rarity finally agrees. During the trip, Sweetie Belle faithfully lugs Rarity' trunk-laden wagon. Rarity comforts her sister when she is afraid of Rainbow Dash's scary campfire stories. When they arrive at their destination, Winsome Falls, Sweetie Belle suggested that the sister teams would race each other to the falls. Rarity feigns reluctance at first but then happily takes off running with her sister.
When Sweetie Belle appears in Just for Sidekicks, it appears that she is picking up some of her sister's traits, including a fashion sense (saying that she isn't "dressed" for the Crystal Empire), and Rarity's high-pitched squeal.
In One Bad Apple, Sweetie Belle suggests they tell Rarity about the Cutie Mark Crusaders' bullying problem after Scootaloo and Apple Bloom said not to telling Applejack, showing that Sweetie trusts her sister. However, since the crusaders shot down that idea too, they didn't inform Rarity.
In For Whom the Sweetie Belle Toils, Sweetie Belle gets angry at Rarity when the clothes she made for a play starring herself and the other Crusaders get more attention then the play itself. That night, she sabotages a headdress Rarity made for Sapphire Shores. Afterwards, Princess Luna appears to Sweetie Belle in her dreams, helping her work through her feelings towards Rarity (even helping her realize that a time at her fifth birthday party when she thought Rarity had stolen attention from her was not what she thought). Remorseful over her actions, Sweetie Belle leads the Crusaders to Canterlot in order to fix the headdress. She fixes the sabotage, and reconciles with Rarity.
Outside of the episodes featuring the Cutie Mark Crusaders, Rarity doesn't appear often with her sister.
Giving a pep talk to the other two Crusaders.Sweetie Belle's comparatively genial nature often makes her a voice of reason among the Cutie Mark Crusaders, and like Apple Bloom and Scootaloo, she has assumed the role of leadership in the group at different times. In Ponyville Confidential, she takes charge of the Crusaders' foray into journalism by inspiring and encouraging the other two fillies. However, Sweetie is also the first to voice her concerns about their libelous gossip column. In Hearts and Hooves Day, she directs the brewing of the love potion intended for Cheerilee and Big McIntosh, helps formulate a plan to trick the two into drinking it, and discovers that the love potion has adverse side effects. She later comes up with a new plan to break the spell, and her friends work together to successfully carry it out. In One Bad Apple, Sweetie suggests several times that they tell Applejack about Babs Seed's bullying of the trio, but Apple Bloom and Scootaloo refuse for fear of being labeled snitches, although they realize Sweetie Belle had the right idea when the conflict is resolved.
In the episode Stare Master, Sweetie Belle stops Apple Bloom and Scootaloo's pointless argument, firmly saying that arguing "is not their special talent". However, at the beginning of The Return of Harmony Part 1, Sweetie Belle argues with Scootaloo over the meaning of the Draconequus statue. Sweetie Belle suggests that the statue represents evil, and calls Scootaloo a "dodo bird" for insisting otherwise. Neither wants to accept the other's interpretation, and all three Cutie Mark Crusaders start fighting. Cheerilee intervenes and tells them that they were all correct, but assigns an essay as punishment. The Crusaders stop fighting, but continue to bicker. Unfortunately, their disharmony hastens the release of Discord himself.
Sweetie Belle has been shown to be a bit slow on the uptake on occasion, and is often the last one to make a comment or completely understand a situation. A prominent example of this trait is in Stare Master. For instance, when her friends speak to Fluttershy in her home, she awkwardly chimes in, "Um, yeah! What they said." Soon afterwards, when Scootaloo and Apple Bloom briefly pretend to be a monster from the Everfree Forest, Sweetie Belle meets their playfulness with a blank stare for a moment before realizing it is a game. While she is not as on-the-spot as her friends, this seems to allow her to think things more carefully, such as when she later keeps her friends from being distracted as they wander through the Everfree Forest. She also tends to ask others to explain things more than once, such as in The Show Stoppers. In the same episode, she is also the third of her friends to announce their goal, which is the nonsensical "no meal uncooked."
- "Why does everypony think I'm gonna sing?"
- — Sweetie Belle
Sweetie Belle singing loudly.In The Show Stoppers, Apple Bloom describes Sweetie Belle's voice as "totally awesome". When the Crusaders are about to go onstage for their performance, Twilight Sparkle is surprised to learn that Sweetie Belle does not have a singing role. However, Sweetie Belle says that she dislikes the idea of singing in front of a crowd. Sweetie Belle's showmanship and powerful voice overpower those of Fluttershy in Stare Master when Sweetie Belle turns Fluttershy's lullaby into a lively gospel-style song. In Hearts and Hooves Day, she leads the The Perfect Stallion song. In Sleepless in Ponyville, when singing the campfire song 99 Buckets of Oats On the Wall after Scootaloo suggests it in order to stay awake and avoid having nightmares, she sings terribly.
Sweetie Belle writes the basic lyrics for the Cutie Mark Crusaders theme song in The Show Stoppers. Later, when Scootaloo is struggling to come up with additional lyrics, Sweetie comes up with some effortlessly. Scootaloo calls her lyrics "awesome".
The Cutie Mark Crusaders cape made by Sweetie Belle with Rarity's fabric.In Stare Master she gave her fellow Cutie Mark Crusaders matching capes that she made by ruining Rarity's beautiful golden fabric, forcing Rarity to work overnight. During The Show Stoppers Sweetie struggles with making costumes for the trio and creates a sweater with 5 legs before Apple Bloom suggests she uses the dress form, to which Sweetie Belle responds "Oh, is that what that's for?"
Aside from fabricating costumes for the Cutie Mark Crusaders, during The Show Stoppers, Sweetie Belle was also in charge of making props for their performance. But Sweetie Belle did not clean up the paint brushes in-between colors resulting in the backgrounds being colored in messy brown and in other brownish colors. Sweetie Belle herself admits that she was curious as to why the colors "looked like mud".
Rarity bearing witness to another one of Sweetie Belle's miracle workings.At the beginning of Sisterhooves Social, Sweetie Belle's mother instructs her in cooking. Rarity awakens to the smell of smoke and rushes downstairs to find that Sweetie Belle had started a fire. She incinerates all of the food she prepares, including juice and liquefied toast. After Rarity remakes the breakfast, Sweetie Belle is allowed to add the garnish to a plate of eggs. She doesn't damage the food but manages to break a table in half. Near the end of the episode, Rarity walks into the kitchen to see that it is a mess again. Sweetie Belle comes out presenting an unburnt pie.
Sweetie Belle has not been shown to be able to perform magic throughout the first three seasons, though her horn sparks briefly near the beginning of One Bad Apple. The sparks are shown to be a light green, similar to her eye color.
At the beginning of Twilight Time, Sweetie Belle tries lifting a broom with her magic, but is unable to move it more than a couple of feet. By the end of the episode, she's not only able to move the broom, but she also levitates it around the library.
In For Whom the Sweetie Belle Toils, Sweetie uses her magic to open and close a box with Rarity's costumes in it to sabotage them.
Sweetie Belle appears in Friendship is Magic, part 1 as a cameo, scared and huddled next to Apple Bloom and Scootaloo when Night Mare Moon reappears in Princess Celestia's place at the Summer Sun Celebration.
Sweetie Belle makes her first speaking appearance in "Call of the Cutie," when she and Scootaloo stand up for Apple Bloom while she is being ridiculed at Diamond Tiara's cute-ceañera. Sweetie Belle and Scootaloo reveal to Apple Bloom that they also do not have their cutie marks. The trio become friends and form the Cutie Mark Crusaders for the purposes of finding their hidden talents and earning their cutie marks. Sweetie Belle is not revealed to be Rarity's sister until her next appearance in Stare Master.
Lauren Faust has said she does not live with Rarity at Carousel Boutique. This is shown when her parents drop her off with Rarity while they go off for vacation in Sisterhooves Social. In One Bad Apple, her parents' house and Sweetie Belle's bedroom are shown, and also hinted at when Rarity takes a look around Sweetie Belle's room in the German magazine comic Einfach rufus.