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".

Background
Although early press materials for Season 1 mentioned that Kenny had a sister, she was not seen until "Best Friends Forever". According to South Park Studios moderator Willie Westwood, her original design was supposedly similar to Ike's. 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.

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 blue shirt with hearts and pink bottoms. It seemed strange that she was wearing pajamas at all, since it's known she lives in a very poor family. It's possible she got them from her foster parents, or another foster child. She appears to be the size of a first or second grader, though few children this age appear on the series, making it difficult to tell. 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.

Personality
Karen seems to be relatively quiet and timid, indicating shyness. She is also very childlike, but considering her age, this is normal. She is almost always seen with Kenny, however, she may trust Kevin and hide behind him when she's shy. She seems to be very attached to her doll, as she brings it with her everywhere she goes. She usually cries 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. McCormicks 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 her oldest brother, Kevin, are fighting, showing that she seems to go to her mother when she is scared. When all three McCormick children are seen in the Park County Police Center's "Soft room" She is seen crying, asking 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. It is likely she dislikes her father, due to his abusive personality.

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.

Prominence

 * "Best Friends Forever" - Background only.
 * "The Poor Kid" - Appears as a major character. First speaking appearance.