Stacy Hirano is the daughter of Dr. Hirano and Mr. Hirano. Sometime in her life, likely before or during the third grade, Stacy met Candace Flynn and they immediately became the best friends (“Spa Day”). How they met is currently unknown. Stacy is constantly supporting Candace to bust her younger brothers, though it is revealed through her conversation with Jenny that she wants Candace to “give up this busting thing once and for all.” (“Phineas and Ferb-Busters!”) Stacy is the cool head between her and Candace, and seems to be the only one that can calm Candace down in any given situation that Candace is stressed in, whether it pertains to Jeremy or busting her brothers. Stacy herself doesn’t have any issues with Phineas and Ferb, once even insisting Candace goes on the Mix-n-Mingle machine because she believed it would help Candace. (“Cheer Up Candace”) She became The Disco Miniature Golfing Queen while playing miniature golf with Phineas and Ferb while trying to bust them for Candace when Candace was sick (“Put That Putter Away”).
During the Summer Rocks Festival Candace introduced Stacy to Coltrane. During the festival they started showing mutual feelings for each other. Their current relationship status is unknown (“The Baljeatles”). It is revealed in that in the future Stacy becomes the President of Uruguay. (“Phineas and Ferb's Quantum Boogaloo”).
When Phineas and Ferb go around the world to try and make the longest day of summer ever, they meet Stacy’s cousins and other family members when stopping in Tokyo. This shows that Stacy has some Japanese descent in her family tree (“Phineas and Ferb Summer Belongs to You!”).
She discovered that Perry was a secret agent. Perry and Stacy didn't want the Flynn-Fletcher's to know about it. His identity is now kept as a secret. ("Happy Birthday, Isabella").
Stacy, in a similar way to Candace, has her own set of trademark clothes. This includes a turquoise T-shirt, along with both a blue skirt and bow. She wears a blue bow on her head which is her trademark look, according to Candace. Candace and Coltrane happen to like her bow. According to Candace, the bow makes Stacy look cute (in both “Hide and Seek” & “The Baljeatles”). As to how the bow is in her hair, its actually on a hairband, seen when Candace wakes her up one morning by calling her on the phone (in “Phineas and Ferb Summer Belongs to You!”). She is also slender.
Stacy also has a purple bracelet on her left wrist and light blue stockings paired with black Mary Jane shoes. She also has fair skin, brown eyes, and long black hair. She also has a resemblance to Ginger Hirano, who is one of the Fireside Girls and her younger sister.
Stacy's Friendship With Candice
She and Candace are best friends. They are usually seen talking to each other and their cellphones or hanging out at Candace’s house.
Stacy is always there for Candace whenever she needs help. She also and takes it very seriously, no matter how repetitive or irrational the situation at hand is. For example, she gave Candace advice on what clothes to wear for the singing contest. She also helped Candace face her stage fright by telling her that she is a fighter, not a quitter (“Flop Starz”). She teamed up with Candace against Phineas and Ferb in a Tree House Fight with them as the winners in the end (“Tree to Get Ready”). She also teaches Candace how to roller-skate. Thanks to her, Candace is getting the hang of it (“Crack That Whip”, “Vanessassary Roughness”).
She cared for Candace, and tried to bust the boys, while she was sick (“Put That Putter Away”). At Jeremy’s pool party, she tells Candace that she is a better person than Nicolette (“De Plane! De Plane!”).
In the Superduper Mega Store, while trying to find a gift for Jeremy, she helped Candace get the Pizzazium Infinionite (which they thought was a lantern) from Buford, Baljeet, Ferb, Vanessa and Perry (“Vanessassary Roughness”). After accidentally sending bad pictures of Candace to Jeremy’s phone, she and Candace got a job at Mr. Slushy Dawg in order to get the phone and delete the photos (“The Bully Code”).
Helping Candace get Jeremy’s attention
Stacy has no personal feelings for Jeremy of her own and willingly aids her in trying to get his attention. One time, Stacy advises Candace to just call and ask Jeremy to the Falling Star Girl’s Choice Dance “don’t let fear rule your life” word of wisdom to Candace. She also mentioned that Jeremy will not say no to her. (“Out to Launch”) She told Candace that she found out through the grapevine that Jeremy was going to ask her out for a very special evening that night and joked with Candace with her as the doctor of Love or “Dr. Jeremy.” (“Chez Platypus”) One time, she advises Candace to play “hard to get” with Jeremy. (This is the only advice from Stacy so far that Candace didn’t follow.) (“At the Car Wash”) Now that Candace and Jeremy are in a relationship, Stacy’s role in Candace’s love life has changed to giving advice to keep the relationship upheld, for which she is rarely called.
Helping Candace Bust the Boys
Stacy sometimes tries to help Candace bust Phineas and Ferb. Every time she tries, however, she couldn’t help but have fun with their projects. One example is when she was taking care of Candace when she was sick and Candace asked her to bust her brothers in her place. She was seduced by the coolness and she got wrapped up in the project instead of getting evidence to bust them (“Put That Putter Away”).
When Stacy was in London, with the Flynn-Fletcher Family, she along with Candace participated in busting the boys using Sherlock Holmes’ method of deduction. After the mystery of what they were doing was solved, however, she again decided to take part in Phineas and Ferb’s big idea, which was in this case, a water slide going down from the Big Ben clock tower (“Elementary My Dear Stacy”).
Stacy once suggested Candace focus on the invention rather than the boys. As flawless as the idea seemed, however, it failed. (“Don't Even Blink”) Stacy, along with Jenny go to “Bust Camp” to train to bust Phineas and Ferb with Candace. However it didn’t work out in the end (“Phineas and Ferb-Busters!”).
Strength of Their Friendship
Stacy and Candace's friendship is a pretty strong one. Stacy continued to be Candace's best friend, even after all the things Candace did to her while trying to impress Jeremy and ended up ruining their day. (“Spa Day”) A true test of their friendship is when Stacy easily welcomes Candace back after an argument outside Candace's house about choosing between their friendship and her desire to bust Phineas and Ferb. (“The Lemonade Stand”).
- Stacy once said she cleaned up her room with only her bare feet. ("Candace Gets Busted").
- Sometimes, her name is misspelled "Stacey".
- In the episode "De Plane! De Plane!" Stacy's hat is shown as white, then bluish-purple, and then white again.
- Sometimes, the fold on the right side of her shirt is on the left instead. ("Canderemy").
- Stacy's mother is the doctor who performs the tonsillectomy on Isabella Garcia-Shapiro. ("I Scream, You Scream").
- Stacy can sing and play the guitar, also she played left-handed as seen in "Phineas and Ferb Get Busted!".
- Hirano is one of 24 wards (districts) that make up the city of Ōsaka, Japan. It literally means "level field". Her surname is that due to her family/descendants being Japanese ("Phineas and Ferb Summer Belongs to You!").
- Stacy got her ears pierced in the episode "I, Brobot".
- Stacy and Candace are winners of a contest to meet the rock band The Bettys and have performed with them on stage. ("Ready for the Bettys").
- Closed Captioning occasionally misspells her last name as "Gerado" ("I, Brobot").
- According to Speed Demons, Stacy once spilled grape juice on Linda Flynn's sweater which Candace has borrowed without asking.
- The first episode that focused on Stacy is "Put That Putter Away". Stacy likes to have fun just like Phineas and Ferb do.
- Stacy enjoys shoes, as seen in "Day of the Living Gelatin" when she makes her gelatin in the shape of shoes, and in "Elementary My Dear Stacy" when she loves to go shopping for shoes in London.
- She does not know what airline food is. ("Cheer Up Candace").
- She does not speak Spanish or Pig Latin. ("The Bully Code").
- She has a poster of the Bettys in her room, then later of the series a poster of the Paisley Sideburn Brothers.
- In the episode "Unfair Science Fair Redux (Another Story)", her name is spelled Stacey on Candace's cellphone.
- She is very skilled in mini golf, and is nicknamed "The Disco Minature Golfing Queen". ("Put That Putter Away").
- Often, Stacy is portrayed as being somewhat flighty and unfocused, which is why her mother insists that she should be more focused on grades and be more serious. ("Put That Putter Away", "The Secret of Success", "Robot Rodeo").
- Stacy's mother wants her to become a doctor or lawyer ("The Secret of Success").
- In the future, a conversation with Candace reveals that Stacy becomes the President of Uruguay. ("Phineas and Ferb's Quantum Boogaloo").
- She is one of the few people to notice a pattern, and claims that she is the only person not to say "Where's Perry?" in "Bad Hair Day", although in she had already said it once in "Put That Putter Away". "Put That Putter Away" may have taken place after "Bad Hair Day".
- It is revealed that Stacy wants a car in Phineas and Ferb The Movie: Across the 2nd Dimension, just like Vanessa.
- In "The Baljeatles" it was revealed that Jeremy's nickname to Stacy is "Staceroo". Also, Candace often calls her "Stace", like in "Elementary My Dear Stacy".
- Her name in Japanese is ステイシー平野 (Suteishī Hirano).
- She did not have an alternative version of herself in the movie, like Carl Karl.
- According to her Top Trumps card in a Phineas and Ferb version of the game, she is into figure skating. This may be canon as a girl who looks very much like Stacy figure-skated in "S'Winter".
- Jeff "Swampy" Marsh has confirmed that Stacy is Ginger Hirano's older sister.  This is also referenced in "For Your Ice Only".
- Stacy and Ginger sometimes appear on the same episodes. But until "For Your Ice Only", none of them had Stacy and Ginger interact.
- Stacy is probably 15 or 16 years old, since her birthday was mentioned in "Doofapus". She is the first (and only character) so far to not appear on their episode they had a birthday on.
- She may practice (or have practiced), a sport, it has trophies and medals in his room ("Canderemy").
- She knows about Perry's secret identity.
- Disney Wiki