Ruka's twin older sister. Rumi is more tomboyish than Ruka, but they make a little difference such. Rumi and Ruka loved Katsuyuki but Katsuyuki fall in love with Ruka. Since her envy and hatred for Ruka have been increased by virus, she turn into evil. When she get supernatural power same as Ruka, Rumi gets ability to control a person with a virus to transmit from her saliva and blood. Rumi does much murder to obtain Katsuyuki's love. however, she feels pains whenever she murders a person, she cannot sleep without drugs. at last, Rumi hopes that she is killed by Ruka. author tells that if Katsuyuki falls in the love in Rumi, twin names in the story are only replaced.