- “I'm a magical princess from another dimension!”
- ―Star introducing herself to Marco
Star is extremely energetic and friendly. She loves having fun, and she usually has an optimistic outlook on life. She loves to help others and whenever she sees that someone is upset, she does her best to cheer them up. She is a bit reckless, as she enjoys fighting monsters and doing wild things. She is also stubborn at times, as she often does things her own way and not listening to other people's rules or even take advice. Strangers, in her eyes, are just friends she has not met yet, and she feels bad if she hurts someone's feelings, whether intentionally or not. However, Star can be egocentric, wanting attention, and getting frustrated with things that bother her. Thus, she gets jealous very easily. Star has a happy-go-lucky attitude and always puts a smile on everyone's faces. She also works very hard towards her goals, so much that she will sometimes go sleep-deprived.
As the series progresses, Star becomes less prone to resorting to magic to fix a situation and shows a willingness to become stronger, more serious, and not running away from her problems, despite this sometimes resulting in her underestimating her enemies. After Toffee's defeat, she decides to focus on becoming a better princess and starts to act more serious and mature as a result.
Star is a fair-skinned fourteen-year-old (Fifteen as of Stump Day) girl with light blue eyes and long blonde hair that goes down to her knees. Her cheeks have posh pink hearts, which sometimes change into things that reflect her emotions, such as hourglasses when she is bored, grey skulls when she is pumped for battle, white skulls when she is depressed, or light bulbs when she has an idea.
With nearly all her outfits, she wears a red or pink headband with horns.
During her Mewberty period, Star had purple hearts appear all over her skin until she eventually turned completely purple and acquired an insect-like appearance. Her hair turned pale lavender twisted into two buns, her eyes were replaced with glowing hearts, and gained four extra arms and butterfly-like wings. After her Mewberty phase, she reverted back to normal but left with a small pair of wings on her back, often hidden by her hair. In her second Mewberty form, Star's eyes become yellow four-pointed stars, her skin becomes a lighter shade and gains an extra two pair of arms like before along with large fiery gold wings. Her hair also appears as a lighter shade of blonde in two long bun braids. After she gains full control over the form, her eyes appear as their regular blue, and she does not glow.
Star's adventures start off on her fourteenth birthday, where her Mother bestows upon her their family's greatest heirloom, the Royal Magic Wand. Unfortunately due to being reckless and irresponsible, she causes so much chaos and destruction that her parents decide to send away. At first, she thought her parents were sending her to St. Olga's Reform School for Wayward Princesses, but to her relief, they were sending her to Earth, where she can learn her magic safely. Star was dropped off at her new school in a place called Echo Creek, where she met Marco Diaz, a student at her school, and would be living with during her stay on Earth. During their first meeting, Star immediately took a liking to Marco and declared him a friend, but Marco at the time was not so keen about her because of how chaotic she was, especially with her magic. Marco finally lost it when Star accidentally sucked his room into a black hole, that he decided to run away from home, abhorrent of his new roommate. Feeling sorry, Star found Marco outside a shop and acknowledged the hardship she had put him through. She was planning to find another family to live with, but after a brief battle with Ludo and his monster army, Marco expressed a change of heart toward Star and a preference for her to remain a resident of his home.
Through the course of the first season, Star and Marco go on many adventures, and Star tries her hardest to adjust to life on Earth which for her proves difficult. She even misunderstands many things during her time on Earth, such as thinking Echo Creek Academy's football team was going into a fight to the death with a rival team called the "Warriors" or mistaking a product known as the "Banagic" as an actual magical object. A few times, Star is encountered by Ludo and his monster army who are out to steal her wand but never succeed. She also tried to help Marco with some of his personal problems. It would not be until the near end of season one where Star would meet her greatest enemy of all, Toffee.
When Marco was kidnapped by Toffee, Star set out to rescue him, accompanied by Ludo and Buff Frog. Apparently Toffee was proven to be far too smart for Star that she was forced to surrender her wand to him, only to learn that he wanted her to destroy it. Using a whispering spell, her wand destroyed itself and blew up Ludo's castle along with Toffee and Ludo's former monster army. However, a new tiny unicorn came along to recharge the wand, giving it a new appearance, with half of the star face missing.
Star continued to live with the Diazs, practicing her magic under the tutorials of Glossaryck and handling school life. Star remains reckless and irresponsible, but over the course of the season develops more maturity. Star even struggled with her newly restored wand. Even though it remained reliable, it had not been the same since the day it was destroyed. It was now powered by a unicorn corrupted by an evil force and did not work properly when Star feels negative emotions.
Star's friendship with Marco slowly became very strained, especially when he started dating his long time crush, Jackie-Lynn Thomas. In the episode "Sleepover", a game box called Truth or Punishment revealed that Star had a crush on Marco just as it got crushed by a dump truck. Throughout the second half of season two, Star struggled with her growing feelings for Marco and tried her hardest to ignore them. Marco would not know about Star's crush on him until "Face the Music", when the songstrel, Ruberiot, wrote a song about Star for her Song Day. His song revealed all of Star's deepest and darkest secrets, including her crush on Marco. After that, Star and Marco's friendship became even more strained and the two of them desperately tried to avoid each other. During the end of the school year party on planet Earth, in "Starcrushed", Marco asked Star straight out if she had a crush on him and answered no. She just wanted the two of them to be friends, to which Marco agreed. However, after Star's mother showed up in her room to take her back to Mewni and with news that Toffee had returned, Star confessed to Marco in front of everyone that she does have a crush on him before tearfully leaving Earth at the end of the second season.
Upon returning to Mewni, Star and her mother were on the run from Toffee, who by now had possessed Ludo and taken over the kingdom. When news got out that River and Marco were in trouble, Star wanted to go and rescue them, but her mother would not let her. So, she sneaked away and returned to the castle where she faced the Toffee possessed Ludo. She used the whispering spell to destroy Ludo's wand and was transported to a corrupted version of the Realm of Magic. Toffee had been corrupting all the magic of the multiverse since "Storm the Castle". All the magic was on the verge of being destroyed for good. However, Star manages to use the last vestige of uncorrupted magic to restore the usable magic through the Realm and destroy Toffee for good.
Afterwards, Star set her sights on becoming a better princess, starting with unifying monsters and Mewmans. During this time, she met her distant ancestor, Eclipsa and discovered she could travel through multiple dimensions without the use of Dimensional Scissors as well transform into a magic butterfly like her mother. She also made Marco her royal squire during his stay on Mewni as a foreigner.
By the second half of the third season, Star discovered that Miss Heinous was Eclipsa's biological daughter, Meteora, and all her ancestors dating back to Festivia were not true-blooded members of the Butterfly family. It turned out that the Magic High Commission had replaced Meteora with Festivia and erased all record history of her existence. When Miss Heinous, now going by her real name, regained her true identity she set out to take back what was rightfully hers. When her mother went missing while trying to stop her, Star was made temporary queen of Mewni, and led an army against the now monster Meteora. The battle was almost at lost until Eclipsa took the wand and unexpectedly reverted her daughter back to infancy. Afterwards, Star decided to return the throne and the wand to Eclipsa.
Star begins searching for her mother; eventually finding her on the Island of the Pie Folk where she discovers that Festivia was of Pie Folk origin, meaning that she and Moon are partially of Pie Folk descent. She next spends the first half of the season trying to get the Mewmans to like Eclipsa which proves difficult due to everyone's perceived aspects of her. Soon, Star herself begins to have her doubts when she learns that she desires to release her husband Globgor from imprisonment. This eventually culminates in Globgor getting released and Star realizing that the Magic High Commission has been out to get him and Eclipsa despite their changed ways. Star holds a coronation for Eclipsa and she and Globgor decide to rule Mewni peacefully.
After leaving Mewni behind and giving up her title as princess, Star realizes that she is unsure of what to do with herself. This causes tension between her and Tom that eventually ends with him breaking up with her. She also learns that she is still connected to Marco through the blood moon curse and have the curse "cleaved" so that they can just be friends. Nevertheless, Star maintains a closer friendship to Marco than to Tom.
Everything comes to a head during the events of "Sad Teen Hotline" where Star, Marco and Tom discover that they cannot access Mewni through any teleporting means. They recruit Janna and discover a well that can take them to any place in the multiverse. Upon arriving in Mewni, they learn that Mina Loveberry has acquired an army of Solarian soldiers to eradicate Monsters and rule over the Mewmans with an iron fist. With no other options, Star decides to destroy magic completely by heading straight into the magic realm and performing the whispering spell. This succeeds, but Star learns that she and Marco cannot be together as once the spell is performed, everyone goes back to their respective dimensions. Star and Marco embrace each other as the magic realm closes for good.
Star and Marco's magic ends up being so powerful that both Earth and Mewni fuse into one world and the series ends with Star and Marco reunited for good.
- In earlier conceptual versions of the series, Star was originally a grade schooler who did not have magic powers, but believed she did. After some suggestions, on making Star older and have real magic powers, Daron changed her into a princess from a different dimension.
- Star Butterfly's character was influenced by many anime heroines that Daron Nefcy admired, such as the female leads of Sailor Moon, Magic Knight Rayearth and Revolutionary Girl Utena.
- Daron Nefcy originally wanted Star to be a fourth grader but executives wanted the character to be a little bit older.
- In "Cheer Up Star", she is revealed to have coulrophobia (a fear of clowns).
- Star is the first Disney heroine to have coulrophobia, with the second being Riley Andersen.
- But she appears to not be afraid of clowns anymore as she participated in a ritual with Janna to see Bon Bon the birthday clown.
- In "Diaz Family Vacation", it is revealed that she inherits her passion to fight monsters from her father, who secretly fights monsters himself.
- In "Royal Pain", Star implies that she and other people from Mewni are not humans when she tells her father "Humans put things in there and flush them down." when he inquired about the toilet.
- This could also explain in "Mewberty" when she went through her metamorphosis and why she has butterfly wings as of now.
- Star herself has confirmed in "Mewnipendance Day" that she and the other people from Mewni are not humans. Rather, they are a humanoid species called "Mewmans".
- She dressed up as Ludo for Halloween in "Hungry Larry".
- Most of the time Star's bangs overlap her eyes and eyebrows, possibly due to how large her eyes are drawn.
- It is hinted that Star is bisexual as she is smitten with both Marco and Brunzetta. This would technically make her the first LBGT+ protagonist in a Disney animated series, though she has yet to be identified as such.
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- "Dominic Bisignano Post". Tumblr (August 23, 2017).