Kit is a cat Familiar, a magical creature that guides and protects witches who are new to the craft. She was the Familiar of the Charmed Ones during the first three years after their magic was unbound. As all Familiars, she is a servant of nature.
When the warlock Kimyra began hunting Familiars, Kit went to the sisters for help. In order to communicate with her, the sisters cast a spell that turned Kit into a human. Kit then informed them what was going on and helped them lure the warlock into a trap by being bait. After the warlock was vanquished, the sisters turned Kit into a cat once more so she could continue guiding witches.
When Adam found the Source of All Magic, the forces of nature warned Kit, who in turn warned the Charmed Ones after they turned her human once more. She explained what the Source was and where the sisters could find it. She waited in the manor and sensed it when Adam opened the gate.
Kit asked Patty Halliwell to reverse the humanity spell and disappeared. After Adam was vanquished, she and Dembe appeared at the Source. The guardian told the sisters Kit had found a new location for the Source, so it could never be found again. The sisters were then teleported home.