Ruru is the little girl who stays with the Sendai Aka no Ou. She chides him constantly about his mistakes, even pushing his head into a pillar. She likes playing with her toys in her left hand, making her one of the few left-handed people in the series. She also brings information to Fubuki and Hishigi. Hishigi mentioned that her brother will destroy his laboratory, although whether he actually did this is still unknown. At the end of the manga, the reason why the Sendai Aka no Ou keeps her around is because she has the antibody to the death diseases (the cure and hope of the Mibu people).