|“||You're not gonna find her. Mom's not a ghost, Dad.||„|
|~ Kat to her father.|
|“||I'm starting to forget my mom. Just certain things. The sound of her making breakfast downstairs. The way she'd put on her lipstick, so carefully. I do remember, she always used Ivory soap, and when she'd hug me, I'd breathe her in, so deep. And I remember before I'd go to sleep she'd whisper in my ear, "stardust in the eyes, rosy cheeks, and a happy girl in the morning.||„|
|~ She told Casper about starting to forget her mom, Amelia Harvey.|
Kathleen "Kat" Harvey is the deuteragonist and the love interest of the titular character in the 1995 film, Casper. She also appears in the sequel/spin-off animated series, The Spooktacular New Adventures of Casper.
Kat is a lonely teenager who lost her mother and has a widower father: Dr. James Harvey who is a paranormal therapist, as he contacts the spirits to help them cross through the other dimension while trying to locate his deased wife. Unfortunately, this creates problems for Kat as she and her father has been moving around the country helping other spirits around the world causing her not to have a normal life like most teenagers her age. After being discovered on the News by Casper, who falls for her, he draws the News to Carrigan which lead her into hiring Harvey, so he can get the ghosts out in order for her to collect the treasure hidden inside Whipstaff Manor
When Kat and Dr. Harvey arrived, they were unintentionally scared off by Casper, so Harvey has Kat locked in a closet for safety as he fights with Casper's uncles: The Ghostly Trio and have them trapped inside the vacuumed. The next morning Kat was walking around with a dust-buster as a safe way to guard herself against the Trio. She went inside the kitchen and meet Casper. As she was about the scream, Casper wrapped himself around her face, to let him know that he is friendly and that she with wake his uncles if she screams.
She sat down on the dining table as Casper prepares her breakfast. Dr. Harvey join her as they were confronted by the Trio. Kat argued a bit with the leader Stretch after being disrespectful to their nephew until Harvey intervened, as she was getting ready for school.
At school she was being made fun of by the students, especially by her soon to be rival Amber Whitmire, by her name. She became popular right away after she told them that she lived in Whipstaff and had everyone be invited to the house for a Halloween party. Back at home, she was asked by her crush Vic DePhilippi to be her date at the dance and agree much to Casper's depression. However, it was a plan set up by Amber that she has yet to figure out, wanted to get back at her for unintentionally stealing her spotlight, when the party was originally going to be at Amber's house
That night, Casper does what he can to impress her, but she kept on brushing him off because he is a ghost. Casper took her to the lighthouse where they see the ocean. She asked him about his past, but he couldn't remember. Later in bed, Kat began explaining Casper about her mother and how she remembers the good times she had with her and wonders if her mother would forget about her as well.
The next morning, Kat went into an old attic and found a box that was filled with Casper's old stuff and redecorate the attic. When Casper woke up, she gave him a little tour of his old toys and a handprint of his human self making him realize that he has five fingers in each hand. After remembering everything, Casper gave Kat a dress his mother use to wear as Kat decided to use it for the party. He also showed her a sled, to which he explains his tragic death in that he has suffered a pneumonia attack after a sledding accident. Kat wonders what it was like to die to which Casper explained like being born, but only backward, and that he didn't go where he was supposed to go, so he stays behind to keep his father company. They both saw a news paper saying that J.T. McFadden was haunted by the ghost of his dead son and invented a machine to bring him back to life called the Lazarus.
Casper took Kat to the machine as they were being followed by Carrigan and Dibs. Casper had given Kat experience with his father's invention, one in particular is called the Up and At'em Machine. Inside the lab, Casper showed her around.
She activated the Lazarus, by pressing the button of a book that she found lying on the table. With the Lazarus now risen up, Casper attempted to enter inside the machine, but Kat was beginning to get worried. Casper claims that he's going to be alive. Unfortunately, it all backfires when the glassed capsule that is used to make the entire machine to work was stolen by Carrigan and Dibs which caused Casper to turned into a yolk egg.
Kat helped Casper get back into his own ghost body with an old duster. They were intruded by a ghost of Carrigan, after falling down on a cliff, and took Casper's treasure chest that was contained in a vault and demanded Dibs to get the Lazurus to work, but he double-crossed her and wanted the treasure all to himself, leading Carrigan to send him off flying with his fate unknown.
Casper and Kat tricked Carrigan about unfinished business, as Carrigan stated that she has none causing her to crossover.
The two attempted to try the Lazarus again but was interrupted by a fully ghost Dr. James Harvey and the Ghostly Trio, with Harvey not remember who he was as well as his own daughter. Kat helped him by giving him the pinky promise they had before they moved.
Casper sees that Harvey needs the Lazarus more than him. With Harvey inside, Casper activated the machine and brought him back to life. Kat ran up and embraced her father relieved that he is back alive again. They hear noises realizing that the party was still going on.
With the party going on, Harvey tells Kat to go in and have fun. She and a lot of the party guess see Vic and Amber running away after being scared away by the Ghostly Trio when they originally attempt to sabotage the party.
Later in the dance, everyone, except Kat were dancing in slow music with their partner, as a blonde hair boy appeared before Kat and took her to the dance floor. The boy turned out to be Casper after he had her flown up and gave her the line he said the night before. "Can I keep you?" Kat's mother Amelia who was an angel came to Casper and rewarded him for the sacrifice he made by becoming human for one night only, once the clock struck 10.
After the clock struck ten, Casper kissed Kat as he was slowly transforming back into his ghostly self. The guests were stunned by his appearance as he gave a nervous "boo" causing everyone to leave the party terrified.
Casper, Kat, and Dr. Harvey decided to have the party all to themselves with the Trio dressing as Little Richard performing the Little Richard version of the Casper the Friendly Ghost theme song.
- Eliza Dushku, Kristy Swanson, Scarlett Johansson and Kirsten Dunst were considered for the role of Kat Harvey before Christina Ricci was cast.