Karen McCormick

Karen McCormick is the youngest member of the McCormick family. She appeared as a background character in "Best Friends Forever". She later appeared in "The Poor Kid", where she played a minor role. Kenny is very protective of her, using his Mysterion identity to comfort her in hard times and keep her out of danger. Kenny's protectiveness extends to such a degree that she considers him her "guardian angel". She, along with her mother, can be encountered in South Park: The Stick of Truth.

Background
Although early press materials for Season 1 mentioned that Kenny had a sister, she was not seen until "Best Friends Forever". The original script for the episode "Starvin' Marvin" mentioned a sister in the final scene at the McCormick family dinner, although she was not seen in the episode itself. In "Best Friends Forever", she appeared briefly with her family at an amusement park and at the hospital visiting her brother, but she never speaks nor is she referred to. Her name first appeared on Wikipedia, attributed to Matt Stone. Her name was not confirmed until "The Poor Kid", which focused on her and Kenny's close relationship after their parents were arrested.

South Park: The Stick of Truth
Karen can be found in the McCormick house watching TV. She says that Princess Kenny texted her about how cute Douchebag is, and asks Douchebag to protect her "sister" for her.

Appearance
She looks very similar to Heidi Turner, she has the same hairstyle, although it is a darker shade of brown closer to her father's color, and a green jacket like Heidi's, but with a plum collar and mittens instead of red ones. In her first appearance, she has dirt over much of her face, and her hair is slightly messier, but by her second appearance, she is clean besides dirt over her left eye. For pajamas, she wears a pink-collared light blue shirt with pink and purple hearts and pink bottoms. She appears to be the size of a first or second grader, though few children this age appear on the series. Her appearance was significantly cleaned up in "The Poor Kid". Her jacket no longer has the scrapes or tears, her face is not as dirty, her hair is not as messy, and she has no mittens. In "The City Part of Town", her appearance has been slightly upgraded with her hair now tied back in pig tails.

Personality
Karen seems to be relatively quiet and timid, thus indicating shyness. She is almost always seen with Kenny. She is usually seen crying when dealing with stressful situations.

Kenny McCormick
Karen is Kenny's sister. She seems to have a good relationship with him, especially his alter-ego, Mysterion, to such an extent she considers him a "guardian angel". She also seems to look to Kenny for protection and comfort when she is upset; this is shown when the McCormick siblings are in The Soft Room at the police station and Karen is clutching Kenny's arm. Kenny is extremely protective of her.

Mrs. McCormick
She is Mrs. McCormick's only daughter. She seems to love her mother dearly, even after being through years of abuse likely due to her parents' fighting. Karen can be seen being held by her mother, crying, when her father, Stuart, and Kevin are fighting, showing that she seems to go to her mother when she is scared. When all three McCormick children are in The Soft Room she immediately asks if she can see her mother.

Stuart McCormick
She is Stuart's daughter. They have never interacted one-on-one, so little is known about their relationship.

Kevin McCormick
She is Kevin's sister. She does not seem to be as close to Kevin as she is to Kenny, as she hold Kenny's arm in The Soft Room in the episode "The Poor Kid". However, in "Best Friends Forever", she is seen hiding behind Kevin in the hospital. It's likely that she trusts Kevin. In "The City Part of Town", it is shown that they share a bedroom.

Prominence

 * "Best Friends Forever" - Background only.
 * "The Poor Kid" - Appears as a major character. First speaking appearance.
 * "The Magic Bush"- Background only
 * "The City Part of Town"