Kamineko (「噛み猫」, "Biting Cat", or "Evil Cat" in Japanese) is a gray cat that Sakaki occasionally sees on the way to and from school. Having a great soft spot for cats, Sakaki tries to pet it, but it ends up latching its huge, beartrap-like teeth onto her hand. This becomes one of the series' biggest running gags. Kamineko seems to bear Sakaki strong malice, and at one point attempts to rally an entire neighborhood's worth of cats to attack her. Tomo has somehow managed to get her hands on a plush version of Kamineko, complete with bear trap teeth.
One crucial moment is when Kamineko appears right after the girls have returned from Okinawa, and learned that Maya's mother has died from being run over by a car. As the new leader of the cats since Maru-chan moved away, Kamineko tries to attack Sakaki and Chiyo-chan, but fails to do so because Maya, being an indimidating Iriomote wild cat, scares Kamineko and the other cats away. Since Sakaki finally got a cat of her own, she no longer tries to pet Kamineko, and even apologizes to the cat once for always trying to pet it against its will. Kamineko then tries to fool Sakaki into thinking it wants her to pet it now (which is partly true because it wants an opportunity to bite her), and when she does, Kamineko bites her as usual. This leaves Sakaki slightly confused.