Kimberly Pine, known to nearly everyone as Kim, is the drummer for the garage band Sex Bob-omb and a central figure in the story's exploration of friendship and regret. She is a young woman of average height with fair, freckled skin and distinct red hair, usually styled in a shoulder-length bob, though in flashbacks to her high school years, it is seen long and tied in a ponytail.

Kim's personality is defined by a sharp, sarcastic wit and a deeply ingrained misanthropy, often serving as the voice of cynical reason amidst the chaotic lives of her bandmates. She is not effusive or openly warm; instead, she expresses herself through dry comments and a perpetually unimpressed demeanor, rarely offering a sincere smile, particularly toward Scott Pilgrim, with whom she shares a complicated history. This hard exterior, however, masks a more vulnerable interior. She has hinted feelings of inadequacy, notably lamenting her own appearance compared to the glamorous Envy Adams, and privately envies Ramona Flowers's self-possessed confidence and natural charisma. Underneath her layers of sarcasm and irritation lies a deeply loyal and caring individual, especially when it comes to Scott, despite her frequent exasperation with his behavior.

Kim's backstory is essential to understanding her role and motivations. She was Scott Pilgrim's first girlfriend during their high school days in Northern Ontario, where they played together in a band called Sonic & Knuckles. Their relationship, which included their first sexual experiences, ended not through a dramatic fight but from geographic necessity when Scott moved away to Toronto, leaving Kim feeling abandoned and nursing unresolved hurt. She eventually moved to Toronto herself, and, alongside Scott and Stephen Stills, helped form Sex Bob-omb, forcing a dynamic where she remains close friends with her ex-boyfriend while never fully letting go of the pain of their past. She works at a video rental store called No-Account Video, a job that serves as a mundane backdrop to the band's exploits.

Within the group, Kim acts as the anchor and the conscience. Her primary role is the band's drummer, and she is typically the one to count them into a song, often with a shouted variation of "We are Sex Bob-omb!" that is more a battle cry than a simple introduction. Her relationship with Scott is the most complex; she openly mocks his poor decisions and his obliviousness, but she is also the first person to offer him a place to crash and the tough love needed to pull himself together when his life falls apart. She maintains a professional and friendly rapport with her co-worker Hollie Hawkes, though this friendship is ultimately destroyed when Hollie begins dating Kim's boyfriend, Jason, behind her back. Her living situation with a revolving door of annoying roommates, as explored in side stories, further fuels her low-grade, simmering frustration with the world around her.

Development for Kim comes through a slow release of her pent-up resentments. She spends much of the narrative carrying a torch for Scott that he seems willfully ignorant of, even as he cycles through relationships with Knives Chau and Ramona Flowers. In a moment of crisis when Scott is mentally broken after losing Ramona, he makes a desperate, fleeting attempt to rekindle their old romance. Kim allows herself a moment of happiness before realizing it is born of his despair, not genuine love, and she ultimately rejects him, demonstrating significant emotional maturity. This marks a turning point where she begins to move past her role as the scorned ex. Her fierce loyalty is undeniable; when Scott apologizes to her for his past selfishness, it earns him her genuine support, leading her to defiantly rally the band to fight against the final evil ex-boyfriend, Gideon Graves. In the end, she and Scott find a healthier dynamic, moving on to form a new two-piece band called Shatterband, suggesting she has finally found a way to channel her energy into a creative partnership free from the baggage of their teenage romance.

As a drummer, Kim provides the rhythmic backbone for Sex Bob-omb, but her notable ability is less technical and more emotional. She possesses a unique form of tough-love motivation, capable of cutting through nonsense with a single acidic comment or inspiring her friends to action with a sudden, aggressive shout. Her fighting spirit, when fully unleashed, is formidable; she proves herself unafraid to stand up to powerful villains and is willing to bend the truth or put herself in danger to protect those she cares about, making her far more than just the sardonic observer of the group.