Karen, the main character of Karen Bee, is one of Koyomi's sisters. She's older than Tsukihi and enjoys doing outdoor activities. Despite being younger, Karen is taller than Koyomi, much to Koyomi's dismay. In Karen Bee, her hot-headed personality and her habit of acting before thinking lead her to be stung by a bee, which lead to being poisoned with a terrible fever that lasted for 3 days. Like Hitagi, she refused any help from anyone which eventually leads to her and Koyomi fighting each other.